Cell Biology | DNA Transcription 🧬
الملخص
TLDRVideon från Ninja Nerd handlar om DNA-transkription, vilket är processen där DNA omvandlas till RNA. Den täcker reglerande element och enzymer som deltar i processen, såsom RNA-polymeras och transkriptionsfaktorer. För prokaryoter sker transkriptionen med ett RNA-polymeras som består av core enzym och en sigma-enhet medan eukaryoter använder tre olika RNA-polymeraser och flera allmänna transkriptionsfaktorer. Videon diskuterar även post-transkriptionella modifieringar som capping, poly-A svans och splitsning av introner och exoner. Alternativ RNA-splitsning förklaras, där samma gen kan leda till olika proteiner beroende på hur mRNA splitsas. Skillnader i transkriptionella processer mellan prokaryoter och eukaryoter tas också upp, inklusive rho-beroende och rho-oberoende terminering samt eukaryotisk genreglering med enhancers och silencers. Videon avslutas med en diskussion om RNA-redigering, där exempel ges på hur samma RNA-sekvens kan modifieras för att producera olika proteiner i olika celltyper.
الوجبات الجاهزة
- 📘 Förståelse av DNA-transkription och dess definition.
- 🔍 Skillnad mellan prokaryotisk och eukaryotisk transkription.
- 🧬 Roller hos RNA-polymeras i transkription.
- 📍 Vikt av promotorregioner i transkription.
- 🛠 Funktion av 5'-cap och poly-A-svans i mRNA.
- 🔄 Alternativ RNA-splitsning och dess betydelse.
- 🚀 Roll av enhancers och silencers i genreglering.
- 🛑 Mekanismer för terminering av transkription.
- 🧪 Post-transkriptionella modifieringar i eukaryoter.
- 🌱 RNA-redigering och dess biologiska konsekvenser.
الجدول الزمني
- 00:00:00 - 00:05:00
Introduktion till DNA-transkription. Vi kommer att förklara processen där DNA omvandlas till RNA i både eukaryota och prokaryota celler. För att denna process ska ske behövs vissa proteiner eller enzymer.
- 00:05:00 - 00:10:00
Fokus på prokaryota celler och deras behov av RNA-polymeras holoenzym, som består av kärnenzym och en sigma-subenhet, för transkriptionen. Promotorregionens roll i DNA beskrivs.
- 00:10:00 - 00:15:00
RNA-polymeras holoenzym läser DNA:s templatsträng för att syntetisera RNA. Prokaryota celler kan producera mRNA, rRNA och tRNA från en enda RNA-polymeras.
- 00:15:00 - 00:20:00
I eukaryota celler krävs specifika RNA-polymeraser och transkriptionsfaktorer. Tre RNA-polymeraser (I, II och III) ansvarar för produktionen av olika typer av RNA.
- 00:20:00 - 00:25:00
Transkriptionsfaktorer och deras roll i bindningen till promotorregioner i eukaryota celler beskrivs. RNA-polymeras I producerar rRNA, polymeras II producerar mRNA, och polymeras III producerar tRNA.
- 00:25:00 - 00:30:00
Processen för initiering av transkription i eukaryota celler: polymeras II och generella transkriptionsfaktorer binder till promotorregioner. Jämförelse mellan prokaryota och eukaryota system.
- 00:30:00 - 00:35:00
Elongering i transkription: RNA-polymeras öppnar och stabiliserar DNA-strängar och syntetiserar mRNA genom att läsa DNA-templatsträngen i 3'-5'-riktning.
- 00:35:00 - 00:40:00
Förklarar 5'-3'-läsning och syntes av RNA med hjälp av diagram för att illustrera processen.
- 00:40:00 - 00:45:00
Diskussion om hur RNA-polymerasers funktion kan hämmas av olika ämnen och vilka konsekvenser det får för cellerna. Termineringsprocessen i transkriptionen introduceras.
- 00:45:00 - 00:50:00
Termineringsprocessen i prokaryoter kan ske via rho-beroende eller rho-oberoende mekanismer. Beskrivning av hur rho-protein och hårnålsslingor påverkar processens avslutning.
- 00:50:00 - 00:55:00
Eukaryota celler använder polyadenyleringssignal för att avsluta transkriptionen. Enzymer klipper bort RNA från DNA och RNA-polymeraset.
- 00:55:00 - 01:00:00
Post-transkriptionella modifieringar i eukaryota celler innebär 5'-capping och poly-A-svans för stabilitet och transport av mRNA.
- 01:00:00 - 01:05:00
Cappning av RNA hjälper till att starta translation och skyddar mot nedbrytning. Poly-A-svansens roll diskuteras i liknande termer.
- 01:05:00 - 01:10:00
Splitsning av pre-mRNA i eukaryota celler tar bort introner och fogar samman exoner. Detta görs med hjälp av snurps, bestående av snRNA och proteiner.
- 01:10:00 - 01:15:00
Exon/intron strukturen i pre-mRNA beskrivs. Splitsningsprocessen avlägsnar introner och fogar samman exoner för att bilda moget mRNA.
- 01:15:00 - 01:20:00
Alternativ rna-splitsning ger möjlighet att producera olika proteiner från samma gen genom att variera exonkombinationer.
- 01:20:00 - 01:25:28
RNA-editering kan leda till olika proteinprodukter från samma mRNA, ett fenomen exemplifierat med apob100 och apob48 i enterocyter och hepatocyter.
الخريطة الذهنية
فيديو أسئلة وأجوبة
Vad är DNA-transkription?
DNA-transkription är processen där DNA omvandlas till RNA.
Vilka är de viktiga enzymerna i DNA-transkription för prokaryota celler?
RNA-polymeras holoenzym med core enzym och sigma subenhet.
Vad är en promotorregion?
En promotorregion är en nukleotidsekvens i DNA som tillåter bindning av RNA-polymeraser och transkriptionsfaktorer.
Vad är skillnaden mellan transkription i prokaryoter och eukaryoter?
Prokaryoter använder ett RNA-polymeras, medan eukaryoter använder tre olika RNA-polymeraser och allmänna transkriptionsfaktorer.
Vad är alternatv RNA-splitsning?
Alternativ RNA-splitsning är en process där samma gen kan ge upphov till olika proteinvarianter.
Varför är det viktigt med 5'-cap och poly-A-svans?
De skyddar RNA från nedbrytning och hjälper till att initiera translation.
Vad är rho-beroende och rho-oberoende terminering?
Rho-beroende terminering använder rho-proteinet för att avsluta transkriptionen, medan rho-oberoende bildar en hårnålsslinga som signalerar terminering.
Vad är post-transkriptionella modifieringar?
Modifikationerna inkluderar 5'-capping, poly-A-svans läggs till och splitsning av exoner/introner.
Vad påverkar hastigheten på DNA-transkription i eukaryoter?
Enhancers och silencers påverkar hastigheten på transkription genom att öka eller minska processen.
Vad är RNA-redigering?
RNA-redigering är en process där nukleotider i RNA kan modifieras för att påverka proteintranslation.
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- 00:00:14what's up ninja nerds in this video
- 00:00:15today we are going to be talking about
- 00:00:17dna
- 00:00:17transcription before we get started if
- 00:00:19you guys do like this video please hit
- 00:00:21that like button comment down in the
- 00:00:22comment section
- 00:00:23and please subscribe also down in the
- 00:00:25description box we have links to our
- 00:00:26facebook instagram patreon
- 00:00:28all that stuff will be there all right
- 00:00:29ninjas let's get into it all right ninja
- 00:00:31so with dna transcription we have to
- 00:00:33have a basic understanding of just the
- 00:00:34definition what the heck is
- 00:00:36transcription
- 00:00:37and it's really a simple thing it's just
- 00:00:38taking dna
- 00:00:40okay double stranded dna with the
- 00:00:41eukaryotic cells and even in prokaryotic
- 00:00:43cells
- 00:00:44and converting that into rna so it's
- 00:00:46taking dna and making rna that's all
- 00:00:48transcription is
- 00:00:49but in order for transcription to occur
- 00:00:52in order for it to take place
- 00:00:53we need two particular types of proteins
- 00:00:56or enzymes if you will
- 00:00:58to facilitate this process and i want to
- 00:01:00talk about those real quick
- 00:01:01because these are very important now
- 00:01:04transcription can be kind of different
- 00:01:07okay and it's important to know the
- 00:01:09differences
- 00:01:09between prokaryotic cells we'll consider
- 00:01:12bacteria in this case
- 00:01:13and eukaryotic cells human cells like me
- 00:01:15and you
- 00:01:17in prokaryotic cells there's a
- 00:01:19particular type of protein
- 00:01:21that is needed in order for
- 00:01:23transcription to take place
- 00:01:25what is that protein so let's say that
- 00:01:27we take
- 00:01:28this dna strand here right we have this
- 00:01:30dna strand
- 00:01:31on this dna strand we have these blue
- 00:01:33portions that i've highlighted here as a
- 00:01:35box with some lines in it
- 00:01:37this right here for right now i want you
- 00:01:39to know is what's called a promoter so
- 00:01:41this is called
- 00:01:43a promoter region now a promoter region
- 00:01:46is a
- 00:01:47particular nucleotide sequence within
- 00:01:49the dna
- 00:01:51and what it does is it allows for
- 00:01:53particular proteins like
- 00:01:54rna polymerases and transcription
- 00:01:56factors
- 00:01:57to bind onto the dna and then start
- 00:02:00moving through the dna
- 00:02:01taking the dna and making rna so that's
- 00:02:04the first thing you need to know is
- 00:02:05within the dna
- 00:02:07there's a particular nucleotide sequence
- 00:02:08we'll talk about a little bit later
- 00:02:10called a promoter region and that's the
- 00:02:12first thing that we need to
- 00:02:14identify let's say that we take this
- 00:02:16particularly for
- 00:02:19prokaryotic cells so prokaryotic cells
- 00:02:23and we'll just say like a bacterial cell
- 00:02:25okay prokaryotic cells use a
- 00:02:28very particular type of enzyme what
- 00:02:31is that enzyme it's called a
- 00:02:34rna polymerase holoenzyme okay so it's
- 00:02:38called an
- 00:02:38rna we're going to put poll polymerase
- 00:02:42holo enzyme
- 00:02:46now that's a lot of stuff let me explain
- 00:02:48what this is and i'll show you the
- 00:02:49structure of it a basic structure of
- 00:02:51what the rna polymerase holoenzyme is
- 00:02:53it's made up of two things one of the
- 00:02:56components of this enzyme
- 00:02:59is called the core enzyme
- 00:03:02and the core enzyme for this rna
- 00:03:04polymerase holoenzyme
- 00:03:07consists of multiple subunits that they
- 00:03:09just love to ask you on your us mles and
- 00:03:11other exams
- 00:03:12and these are they contain two alpha
- 00:03:15units
- 00:03:16okay two alpha chains proteins it
- 00:03:18contains
- 00:03:19two beta units technically we say beta
- 00:03:22and beta prime
- 00:03:23if you really want to be specific and
- 00:03:25then one more
- 00:03:26which is called an omega unit okay
- 00:03:29so these are the primary components of
- 00:03:31the core enzyme which makes up rna
- 00:03:33polymerase what's important to remember
- 00:03:36is that these are what are going to
- 00:03:38really read the dna
- 00:03:39and make rna that portion of the enzyme
- 00:03:42reads the dna
- 00:03:43and makes rna the next component of the
- 00:03:45rna polymerase holoenzyme is the portion
- 00:03:48that we need in order to bind
- 00:03:50to the dna to the promoter region
- 00:03:51without it we won't be able to allow for
- 00:03:53this rna polymerase to bind to the dna
- 00:03:55and transcribe it this is called
- 00:03:58the sigma right or you can represent it
- 00:04:02like this
- 00:04:03subunit or factor if you will okay
- 00:04:07these two components the core enzyme
- 00:04:09which is made up of the two alpha the
- 00:04:10beta and the beta prime and the omega
- 00:04:12sub unit
- 00:04:13as well as the sigma subunit make up the
- 00:04:15entire rna polymerase
- 00:04:16now let me show you for example here
- 00:04:19let's say i represent the core enzyme
- 00:04:21as just this kind of blue circle with
- 00:04:23lines in it
- 00:04:24and then we'll represent the sigma
- 00:04:26subunit as kind of like a pink circle
- 00:04:27with some lines in it right so let's
- 00:04:29imagine here
- 00:04:30we have that core enzyme which we're
- 00:04:33going to represent like this
- 00:04:34and then the other component of it which
- 00:04:36is the sigma subunit which will
- 00:04:38represent
- 00:04:39like this that sigma subunit will then
- 00:04:43bind to the promoter region once it
- 00:04:45binds to the promoter region
- 00:04:47then this core enzyme of the rna
- 00:04:49polymerase will then
- 00:04:50release away from the sigma subunit
- 00:04:54and it'll start moving down
- 00:04:57this dna and as it moves down the dna
- 00:05:00it'll read the dna
- 00:05:01from three to five and synthesize an rna
- 00:05:04strand
- 00:05:05from that which we'll talk about more
- 00:05:07detail later
- 00:05:09from five to three
- 00:05:12so it'll read the dna and make rna
- 00:05:16this rna that we make from in
- 00:05:18prokaryotic cells with the rna
- 00:05:20polymerase holoenzyme
- 00:05:22is very different from eukaryotic cells
- 00:05:25in prokaryotic cells that mrna that we
- 00:05:27made from this one rna polymerase
- 00:05:29holoenzyme can make all the mr
- 00:05:31all the rna we need whether that be rrna
- 00:05:34within the prokaryotic cell whether that
- 00:05:36be m
- 00:05:37rna within the prokaryotic cell or t
- 00:05:41rna within the prokaryotic cells
- 00:05:44so that's very important big thing i
- 00:05:47really need you guys to take away from
- 00:05:48that is
- 00:05:48prokaryotic cells they use one rna
- 00:05:52polymerase which is called a holoenzyme
- 00:05:54made up of two components a core enzyme
- 00:05:56made of these subunits
- 00:05:57and a sigma subunit the core is what
- 00:06:00reads the dna and makes the rna the
- 00:06:02sigma subunit is what
- 00:06:04binds the rna polymerase to the promoter
- 00:06:07region
- 00:06:07enabling it to transcribe the dna okay
- 00:06:11and whenever you make rna within a
- 00:06:13prokaryotic cell from this rna
- 00:06:15polymerase it makes
- 00:06:16all the rnas within that prokaryotic
- 00:06:18cell in eukaryotic cells it's a little
- 00:06:20bit different
- 00:06:22so let's talk about that let's say here
- 00:06:25we have
- 00:06:25three promoter regions that i want us to
- 00:06:27focus on and this is all within
- 00:06:30eukaryotic cells
- 00:06:34in eukaryotic cells we need
- 00:06:38two different things in order to allow
- 00:06:40for transcription to occur
- 00:06:42and this portion here right and this
- 00:06:44portion of prokaryotic cells we only
- 00:06:46need
- 00:06:46one enzyme which had two different
- 00:06:48components
- 00:06:49within eukaryotic cells each process
- 00:06:52requires
- 00:06:53a particular enzyme an rna polymerase
- 00:06:56and a transcription factor let's let's
- 00:06:59kind of write that down
- 00:07:00so let's say that we take this first
- 00:07:01promoter we want to read this gene this
- 00:07:05portion of the dna
- 00:07:06and make rna and this is the rna that
- 00:07:08we're actually going to
- 00:07:10synthesize right here okay from this
- 00:07:13gene
- 00:07:14a particular enzyme let's represent this
- 00:07:16in blue since we've been kind of doing
- 00:07:18blue here there's going to be a
- 00:07:19particular enzyme which is going to
- 00:07:21read this dna okay
- 00:07:24and make this rna there's a particular
- 00:07:26enzyme what is that enzyme called it's
- 00:07:27called rna polymerase
- 00:07:30but this is the first promoter within
- 00:07:33the eukaryotic cells that we're talking
- 00:07:34about right
- 00:07:35so let's call it rna polymerase one
- 00:07:39rna polymerase one will read the dna and
- 00:07:42make a particular type of rna but in
- 00:07:44order for it to do this
- 00:07:46it needs a special protein that can bind
- 00:07:49to the promoter region which allows for
- 00:07:51the rna polymerase to bind to the dna
- 00:07:53and read the dna
- 00:07:54what is that particular protein that
- 00:07:57protein
- 00:07:58let's represent it here in let's do
- 00:08:01green there's a particular protein
- 00:08:05which will bind here to the rna
- 00:08:08polymerase
- 00:08:09and to the promoter and allow the rna
- 00:08:11polymerase to
- 00:08:12bind to the dna and start moving down
- 00:08:15reading the dna and making this rna
- 00:08:17what is this called this is called a
- 00:08:19transcription
- 00:08:20factor tf and there's many different
- 00:08:23types of transcription factors the
- 00:08:26particular thing that i need you to
- 00:08:27remember for right now
- 00:08:29is that we call these transcription
- 00:08:31factors which are utilized by rna
- 00:08:33polymerases
- 00:08:34within eukaryotic cells we call these
- 00:08:38general
- 00:08:40transcription factors we'll talk about
- 00:08:41very specific types
- 00:08:43with an rna polymerase type 2 a little
- 00:08:45bit later but for right now
- 00:08:47two things i need in order for this rna
- 00:08:49polymerase to be able to read the dna
- 00:08:51and make this rna rna polymerase 1 needs
- 00:08:54a general transcription factor
- 00:08:56to bind to the promoter allowing the rna
- 00:08:58polymerase 1 to
- 00:09:00then bind into the dna read it and make
- 00:09:02rna
- 00:09:03what type of rna does it make i have all
- 00:09:06the rnas within prokaryotic cells from
- 00:09:08one rna polymerase
- 00:09:09but rna polymerase 1 makes a very
- 00:09:12particular type of rna
- 00:09:14and this is called r rna
- 00:09:18now rrna is very important because this
- 00:09:21is incorporated into what's called
- 00:09:23ribosomes ribosomes and ribosomes are
- 00:09:27utilized in the translation process
- 00:09:29where we take
- 00:09:30mrna and from that make proteins
- 00:09:34so we'll talk about this later in
- 00:09:35another video but for right now first
- 00:09:36thing i need you know is rna polymerase
- 00:09:38one
- 00:09:38with transcription factors reads the dna
- 00:09:41and makes
- 00:09:42rrna now that makes everything else
- 00:09:44pretty easy from this point
- 00:09:46here's another promoter region of a
- 00:09:48particular sequence of dna
- 00:09:50right within a eukaryotic cell so this
- 00:09:53is the second promoter region
- 00:09:54another enzyme binds another rna
- 00:09:57polymerase
- 00:09:58and not only just that one rna
- 00:10:00polymerase here but we also need
- 00:10:02a set of general transcription factors
- 00:10:06to bind to this promoter region so
- 00:10:09general transcription factors we need to
- 00:10:11bind to the promoter region
- 00:10:12enabling this rna polymerase to bind to
- 00:10:15the dna
- 00:10:15read it and then make what make these
- 00:10:19particular types of rna we have here
- 00:10:23this is well this was the first promoter
- 00:10:26this is the second one
- 00:10:27all right so we're going to call this
- 00:10:29rna polymerase
- 00:10:312 rna polymerase 2 will bind to this
- 00:10:35promoter via the transcription factor
- 00:10:37read the dna and make rna what kind of
- 00:10:39rna is it going to be making
- 00:10:41big thing i need you to remember is it's
- 00:10:43making m
- 00:10:45rna mrna you'll see later again
- 00:10:48is the component it'll have to go
- 00:10:50through some very specific modifications
- 00:10:54that we'll talk about in great detail
- 00:10:56and then eventually
- 00:10:57it'll be translated with
- 00:11:00the help of rrna and another thing
- 00:11:02called trna
- 00:11:04at the ribosomes and making proteins
- 00:11:06okay the other thing that
- 00:11:08you guys can remember if you guys want
- 00:11:09to be scholarly or ninja nerdy
- 00:11:11there's another rna that's made here and
- 00:11:13we'll talk about it a little bit later
- 00:11:15with what's called splicing
- 00:11:17and these are called small nuclear rnas
- 00:11:21and these are involved in what's called
- 00:11:23splicing and we'll get into that a
- 00:11:25little bit more in detail later okay
- 00:11:27but big thing rna polymerase ii with the
- 00:11:29help of general transcription factors
- 00:11:31makes mrna
- 00:11:32and snrnas rna polymerase one with the
- 00:11:34help of general transcription factors
- 00:11:36makes
- 00:11:36rnas when the heck do you think this
- 00:11:38last promoter region of this
- 00:11:40sequence of dna within this eukaryotic
- 00:11:42cell is going to make
- 00:11:44trnas and it's the same process what do
- 00:11:46i need here
- 00:11:47i need general transcription factors to
- 00:11:49bind to the promoter region
- 00:11:51when that binds that facilitates or it
- 00:11:53helps to
- 00:11:54allow the rna polymerase
- 00:11:57type what
- 00:12:00three two
- 00:12:04bind to the dna and then read the dna
- 00:12:07and then synthesize what rna
- 00:12:12what type of rna is it making the type
- 00:12:14of rna that is being synthesized from
- 00:12:16rna polymerase iii is
- 00:12:18primarily trna but
- 00:12:22a teensy little bit of snra is
- 00:12:25also made by rna polymerase type 3.
- 00:12:28and if you guys really want to be extra
- 00:12:30ninja nerdy technically
- 00:12:32even a teensy bit of
- 00:12:36rna is also made here as well okay
- 00:12:39now trna what the heck does this do
- 00:12:41you'll see later
- 00:12:42that this is also involved in the
- 00:12:44translation process
- 00:12:46it carries a particular amino acid and
- 00:12:48an anticodon
- 00:12:50which is going to be involved in that
- 00:12:51process and we'll talk about that in a
- 00:12:52separate video
- 00:12:53so i know this was a lot of stuff to
- 00:12:54take away and take away from this but
- 00:12:56the big
- 00:12:56overall theme that i really just out of
- 00:12:58all of this what i want you to take away
- 00:13:00from this is this quick little thing
- 00:13:01here
- 00:13:02that rna polymerases 1
- 00:13:062 3 remember
- 00:13:10r m t
- 00:13:14rna polymerase 1 primarily gives way to
- 00:13:16rrna
- 00:13:17rna polymerase 2 primarily gives way to
- 00:13:20mrna
- 00:13:22and then rna polymerase 3 primarily
- 00:13:24gives way to
- 00:13:25t rna these are the big things that i
- 00:13:28want you to take away from all this if
- 00:13:29you want to go the extra mile be extra
- 00:13:31ninja nerdy
- 00:13:32two and 3 also can give way to what
- 00:13:36small nuclear rna if you really want to
- 00:13:37go the extra mile technically three can
- 00:13:39also give way to
- 00:13:40rrna but this is the basic thing to take
- 00:13:42away from what we just talked about
- 00:13:45and then the other thing is in
- 00:13:47prokaryotic cells we don't need all of
- 00:13:48these
- 00:13:49we need one rna polymerase holoenzyme
- 00:13:53to make all the rnas one last thing is
- 00:13:57you notice in eukaryotic cells that we
- 00:13:58have particular transcription factors
- 00:14:00that are going to be needed for each rna
- 00:14:02polymerase
- 00:14:03the transcription factor in prokaryotes
- 00:14:05technically if you want to be specific
- 00:14:08is the sigma subunit because it's the
- 00:14:09portion that's binding to the promoter
- 00:14:11to allow
- 00:14:12the core enzyme of the rna polymerase to
- 00:14:14read the dna
- 00:14:15okay so that kind of covers the basic
- 00:14:17concepts of the two main things that we
- 00:14:18need
- 00:14:19in order for this transcription process
- 00:14:21to occur now
- 00:14:23there's one other thing that i want to
- 00:14:24talk about very quickly before we really
- 00:14:26start talking about
- 00:14:27mrna because that's going to be the
- 00:14:28primary topic here i want to have a
- 00:14:31quick little discussion on how we can
- 00:14:33modulate
- 00:14:34the rate of transcription either
- 00:14:36speeding it up or slowing it down
- 00:14:38okay so the next thing i want to talk
- 00:14:39about is very very briefly
- 00:14:41on eukaryotic gene regulation so i want
- 00:14:44to have a quick
- 00:14:45quick tiny little discussion on gene
- 00:14:46regulation
- 00:14:48okay and the only reason i want to
- 00:14:49mention this is because this is very
- 00:14:51easy and it kind of makes sense along
- 00:14:53with what we're talking about
- 00:14:55but we're not going to talk about it in
- 00:14:56prokaryotic cells we're primarily going
- 00:14:58to talk about this gene regulation
- 00:15:00and eukaryotic cells we're going to have
- 00:15:02a separate video because it's more
- 00:15:03involved
- 00:15:04we'll talk about gene regulation and
- 00:15:06prokaryotic cells with the lac operon
- 00:15:07and the tryptophan operon we'll get into
- 00:15:09that
- 00:15:09but in eukaryotic cells there's two ways
- 00:15:12that we can modulate and it's really
- 00:15:13easy
- 00:15:14one way that we can modulate
- 00:15:17transcription is we have particular dna
- 00:15:19sequences
- 00:15:20particular sequences of dna particularly
- 00:15:22palindromic sequences
- 00:15:24which are called enhancers and enhancers
- 00:15:28are basically dna sequences and
- 00:15:30the big thing i want you to take away
- 00:15:32from this they can increase
- 00:15:34the transcription rate so they increase
- 00:15:37the
- 00:15:38rate of transcription or the process of
- 00:15:39transcription okay we'll talk about how
- 00:15:41they do that
- 00:15:43the other thing that can regulate the
- 00:15:45the transcription process or gene
- 00:15:47regulation in a way
- 00:15:48is something called silencers
- 00:15:52in silencers they do what they decrease
- 00:15:55the transcription rate or the
- 00:15:57transcription process
- 00:15:59now it's really straightforward it's
- 00:16:02relatively simple let me explain
- 00:16:04what i mean let's say here we have a
- 00:16:06strip of dna we're going to explain how
- 00:16:08this happens so here's our strip of dna
- 00:16:10and remember this blue region what did
- 00:16:12we call this blue region that we talked
- 00:16:13about above
- 00:16:14this was called our promoter region and
- 00:16:17do you guys remember let's take
- 00:16:19eukaryotic cells in this case what we
- 00:16:21needed in order for this process to
- 00:16:24occur
- 00:16:25we needed a particular transcription
- 00:16:27factor to bind to that promoter region
- 00:16:29and then what else did we need in order
- 00:16:31for that to read the dna and make rna
- 00:16:33you needed a particular rna polymerase
- 00:16:37right so we need an
- 00:16:38rna polymerase depending on which one
- 00:16:40we're talking about
- 00:16:41would depend on the type of rna that we
- 00:16:43want to make
- 00:16:44and then a transcription factor okay
- 00:16:48now this is going to go read the dna
- 00:16:50this rna polymerase will read the dna
- 00:16:52and then make rna right now here let's
- 00:16:55say that we have the promoter
- 00:16:56and you can have this enhancer upstream
- 00:17:00from the promoter or it could be down
- 00:17:02here downstream where we can't see it in
- 00:17:03this
- 00:17:04diagram but it would be all the way down
- 00:17:05here regardless of where it is it's
- 00:17:08usually can be close to the promoter or
- 00:17:10it can be far to the promoter so you're
- 00:17:11probably asking the question how the
- 00:17:13heck would an enhancer that's really far
- 00:17:15away
- 00:17:16influence a promoter that's all the way
- 00:17:18down here how that does it do that
- 00:17:20there's particular structures there's
- 00:17:22different things
- 00:17:24that can activate enhancers and cause
- 00:17:27conformational changes of the dna
- 00:17:30and these are called specific
- 00:17:32transcription factors you know why i
- 00:17:34really frustrate i got
- 00:17:35really deep into talking about specific
- 00:17:37and general transcription factors
- 00:17:39the general transcription factors are
- 00:17:40what bind to the promoter region
- 00:17:42specific transcription factors which
- 00:17:45we're going to really kind of do a
- 00:17:46different color here let's do purple
- 00:17:48specific transcription factors
- 00:17:51will bind to this enhancer region so
- 00:17:54this let's put specific
- 00:17:56transcription factors these will bind
- 00:17:59to the enhancer when they bind
- 00:18:02to the enhancer region it causes a
- 00:18:06looping of the dna to where now the
- 00:18:09promoter was far
- 00:18:10downstream from this enhancer but when
- 00:18:13this
- 00:18:14specific transcription factor binds to
- 00:18:16the enhancer
- 00:18:18it causes the dna to loop in a way that
- 00:18:20it's in very close proximity to the
- 00:18:23promoter region even though it's far
- 00:18:24upstream from it
- 00:18:26and then what was bound to this promoter
- 00:18:28region here do you guys remember
- 00:18:31the general transcription factors
- 00:18:34and what else the rna
- 00:18:38polymerase so now that these are in
- 00:18:42close proximity guess what this
- 00:18:44general trans this uh specific
- 00:18:46transcription factor can do to this area
- 00:18:48over here
- 00:18:49it can act on these proteins and
- 00:18:53stimulate this reading of the dna
- 00:18:56the rna polymerase is to read the dna
- 00:18:58and to do what
- 00:19:00make rna
- 00:19:04whether it be mrna rrna trna so the
- 00:19:06whole point here is that
- 00:19:08enhancers can be either far upstream or
- 00:19:10far downstream which makes it hard to
- 00:19:12interact with the promoter
- 00:19:13but if a specific transcription factor
- 00:19:15binds to that enhancer it creates a
- 00:19:17looping process
- 00:19:18bringing it in close proximity which can
- 00:19:21then stimulate the
- 00:19:22specific transcription factors and the
- 00:19:24rna polymerases which are bound to the
- 00:19:26promoter
- 00:19:27to increase the transcription of rna
- 00:19:30what do you think silencers do
- 00:19:32the exact same process we're not going
- 00:19:34to go into detail of it
- 00:19:35but if you imagine i did the same thing
- 00:19:37i put the silencer here
- 00:19:39and i have a specific transcription
- 00:19:41factor that bound here it's going to
- 00:19:42fold it in a particular way bringing it
- 00:19:44close to the promoter
- 00:19:45inhibiting that promoter region and
- 00:19:47slowing down the transcription process
- 00:19:50it doesn't make sense it's pretty cool
- 00:19:52too right so i need you guys to ask
- 00:19:53yourself the questions because we're
- 00:19:54going to talk about these
- 00:19:56these general transcription factors what
- 00:19:58in the world
- 00:20:00are these specific transcription factors
- 00:20:02and i know that if you guys are the og
- 00:20:04ninjas
- 00:20:05you'll know these processes in and out
- 00:20:08you guys know when we make a protein
- 00:20:10whenever we have like a cell
- 00:20:12signaling response we've talked about
- 00:20:13this a million times here an engineer
- 00:20:15right
- 00:20:16let's say that we take a hormone like
- 00:20:18tsh which stimulates thyroid hormone
- 00:20:20synthesis right tsh will act on a
- 00:20:23particular receptor we call these
- 00:20:25g-protein-coupled receptors right like
- 00:20:27g-stimulatory proteins
- 00:20:29those g-stimulatory proteins will
- 00:20:31activate something called
- 00:20:33cyclic amp cyclic amp will then activate
- 00:20:37something called
- 00:20:38protein kinase a protein kinase a
- 00:20:43depending upon what type of you know
- 00:20:46transcription factor you need in this
- 00:20:48case
- 00:20:48we're going to activate a very specific
- 00:20:51transcription factor
- 00:20:52for making what thyroid hormone
- 00:20:55so some type of thyroid hormone
- 00:20:57transcription factor
- 00:20:58that'll be needed to bind to the
- 00:21:00enhancer change the shape of it
- 00:21:02activate the promoter have the rna
- 00:21:05polymerase
- 00:21:06read the gene that makes what hormone
- 00:21:09thyroid hormone
- 00:21:10and so you'd have this get read you'd
- 00:21:12make an mrna
- 00:21:13that would then get translated and make
- 00:21:17thyroid hormone doesn't that make sense
- 00:21:20how that process occurs
- 00:21:22so we can increase the transcription and
- 00:21:25protein formation of thyroid hormone
- 00:21:26through this process the same thing
- 00:21:28exists
- 00:21:28with steroid hormones if i took for
- 00:21:31example testosterone
- 00:21:33you guys know testosterone right
- 00:21:35testosterone does what
- 00:21:38testosterone will move across
- 00:21:41the cell membrane it'll bind onto a
- 00:21:44intracellular receptor when testosterone
- 00:21:48binds onto the intracellular receptor
- 00:21:49what will that intracellular receptor do
- 00:21:52bind to the enhancer when it binds to
- 00:21:54the enhancer
- 00:21:55loops it brings it close to the promoter
- 00:21:56stimulates the transcription to make
- 00:21:58proteins within muscle so that you can
- 00:21:59get direct
- 00:22:00right that's the whole process of how we
- 00:22:03increase
- 00:22:04transcription and the same thing would
- 00:22:06happen if we wanted to decrease it just
- 00:22:08we would have some type of
- 00:22:10repressing transcription factor binding
- 00:22:13to the silencer
- 00:22:14that would inhibit the transcription
- 00:22:15process so i think we have a pretty good
- 00:22:17idea now of the basic concepts of
- 00:22:19eukaryotic gene regulation
- 00:22:21now spend most of our time talking about
- 00:22:23the transcription particularly of
- 00:22:26mrna all right so when we talk about
- 00:22:28transcription we've had a basic concept
- 00:22:29of it right that we need rna polymerases
- 00:22:31and transcription factors to read the
- 00:22:32dna and make the
- 00:22:34rna but the real one that i want us to
- 00:22:36primarily focus on
- 00:22:38which is primarily important with
- 00:22:40transcription of dna
- 00:22:41is mrna that was the real important one
- 00:22:45now that's in eukaryotic cells with
- 00:22:46utilizing the what
- 00:22:48rna polymerase type 2 in prokaryotic
- 00:22:50cells we would just be using the
- 00:22:52rna polymerase holoenzyme so what i want
- 00:22:54us to do is i want us to go through
- 00:22:56particularly and more d we already have
- 00:22:57a basic concept of how this is going to
- 00:22:59work
- 00:22:59but let's go into the stages of
- 00:23:01transcription particularly for
- 00:23:03mrna within prokaryotic cells in
- 00:23:05eukaryotic cells
- 00:23:06the first stage that is involved here is
- 00:23:09called initiation
- 00:23:11of transcription so the first step that
- 00:23:13we have to talk about is called
- 00:23:15initiation of transcription now this is
- 00:23:18the part that we've pretty much already
- 00:23:20familiarized ourselves with
- 00:23:22okay now within this let's have our two
- 00:23:26cells
- 00:23:26okay that we're going to do initiation
- 00:23:28with we're going to have our prokaryotic
- 00:23:30cells here
- 00:23:31on this left side of the board
- 00:23:34and then over here we're going to have
- 00:23:37the eukaryotic cells here on the right
- 00:23:40side of the board
- 00:23:41what i want us to do is to have kind of
- 00:23:42a comparison a side-by-side comparison
- 00:23:45of the initiation process the first
- 00:23:48thing that we need to know
- 00:23:49is we've talked a little bit about this
- 00:23:51already but this blue region what did we
- 00:23:53call this blue region here again
- 00:23:55this blue region was called the promoter
- 00:23:58region
- 00:23:59now the promoter region i told you is a
- 00:24:01particular kind of like nucleotide
- 00:24:03sequence that is very very specific and
- 00:24:05allows transcription factors and rna
- 00:24:07polymerases to bind to the dna
- 00:24:09it's kind of a signal if you will it's
- 00:24:10like hey here i am come bind to me
- 00:24:13in prokaryotic cells the promoter
- 00:24:16region has particular types of like
- 00:24:19names and just
- 00:24:20weird stuff that they can ask you in
- 00:24:22your exams
- 00:24:24so in the prokaryotic cells they call
- 00:24:26this the third negative 35 region
- 00:24:29which means from the start point at
- 00:24:31which the rna polymerase starts reading
- 00:24:33the dna and making rna
- 00:24:35if you go back 35 nucleotides that's
- 00:24:37kind of the
- 00:24:38point at which the rna polymerases will
- 00:24:40bind
- 00:24:41in prokaryotic cells another one is
- 00:24:44called the negative 10 region
- 00:24:46but they wanted to give this one a name
- 00:24:48so they called it the pribno box
- 00:24:50just meaning that it's negative it's 10
- 00:24:52nucleotides away from that startup
- 00:24:54transcription right
- 00:24:56and then the last one here is called the
- 00:24:58plus one region which is also called the
- 00:25:01transcription
- 00:25:02start site so it's going to be pretty
- 00:25:03much the nucleotide at which you just
- 00:25:05read
- 00:25:06and start making the whole process of
- 00:25:09rna
- 00:25:10so these are the regions that you guys
- 00:25:12need to remember within prokaryotic
- 00:25:13cells these are the kind of
- 00:25:14specific promoter regions and eukaryotic
- 00:25:18cells
- 00:25:19the promoter regions have particular
- 00:25:23nucleotide sequences that we need to be
- 00:25:24aware of
- 00:25:26these are called the top box which means
- 00:25:28that you would have thymine adenine
- 00:25:29thymine adenine
- 00:25:30that would be a particular recognition
- 00:25:32sequence within the promoter and
- 00:25:33eukaryotic cells
- 00:25:35or cat c-a-a-t so cytosine adenine
- 00:25:39adenine thymine
- 00:25:40and the last one is a gc box
- 00:25:43so if there's a tata box a cap box or a
- 00:25:46gc
- 00:25:47box these are identify identifying
- 00:25:49nucleotide areas at which the rna
- 00:25:51polymerase is type 2
- 00:25:53and transcription factors will bind to
- 00:25:56that is the important thing okay now the
- 00:25:59next thing here is
- 00:26:00the polymerases the rna polymerase is
- 00:26:03within prokaryotic cells it's just
- 00:26:05one it's rna polymerase
- 00:26:09holoenzyme right we already kind of
- 00:26:12talked about that with the core enzyme
- 00:26:14two alpha beta beta prime omega and then
- 00:26:16the
- 00:26:16the sigma subunit all of that's needed
- 00:26:19to bind to the promoter region
- 00:26:21and eukaryotic tells us a little bit
- 00:26:22more right we said that we needed two
- 00:26:24things we needed an rna polymerase
- 00:26:26and which what are we making here
- 00:26:28initiation and we're going to say that
- 00:26:30we're trying to make what
- 00:26:31we're trying to make mrna transcription
- 00:26:34so we're doing
- 00:26:34transcription but we're making mrna so
- 00:26:37what was the particular rna polymerase
- 00:26:391 2 3 r m m is
- 00:26:44for r for the mrna so rna polymerase
- 00:26:46type 2 is one of the things that i need
- 00:26:48the second thing that i need is the
- 00:26:52general transcription factors
- 00:26:55and there's just so many of these that i
- 00:26:57don't know how important and how
- 00:26:59specific we really need to go into these
- 00:27:01i'll give you some of them but i just
- 00:27:03want you to know
- 00:27:04that there's so many different types of
- 00:27:06them the main one if you had to remember
- 00:27:09one specific out of the tons of them i
- 00:27:12want you to remember transcription
- 00:27:14factor
- 00:27:142 d this is the one that i really want
- 00:27:17you to remember and the reason why is
- 00:27:20this contains a structure called the
- 00:27:22tata binding protein so this
- 00:27:23transcription factor 2d has a particular
- 00:27:25protein portion
- 00:27:27which binds to the promoter region the
- 00:27:30tata box
- 00:27:31but there's many other reasons region
- 00:27:34transcription factors and you can
- 00:27:36remember these by transcription factor
- 00:27:382 and there can be h there can be e
- 00:27:41there can be f there can be a there can
- 00:27:43be b so there's tons of these dang
- 00:27:45things
- 00:27:46so i don't know how important it really
- 00:27:47is to know that but the main one i want
- 00:27:49you to remember
- 00:27:50is the transcription factor 2d all right
- 00:27:54so these are the things that we need in
- 00:27:55order for initiation to occur
- 00:27:57so let's take for example we're going to
- 00:27:58have on one side
- 00:28:00eukaryotic cells will the eukaryotic
- 00:28:02enzymes will bind
- 00:28:03and on this side the prokaryotic will
- 00:28:05bind right so let's say here we take for
- 00:28:07example we'll make this prokaryotic rna
- 00:28:09polymerase
- 00:28:11we'll make this one blue
- 00:28:14and we'll make the rna polymerase over
- 00:28:16here for the eukaryotic cells just for
- 00:28:18the heck of it
- 00:28:19we'll make it orange okay just so we can
- 00:28:21distinguish the difference between these
- 00:28:23so what will happen this whole rna
- 00:28:26polymerase holoenzyme will do what
- 00:28:31bind to the promoter what will allow it
- 00:28:32to bind what
- 00:28:34subunit of it the sigma subunit and if
- 00:28:37you really wanted to go back
- 00:28:38you guys remember we made that pink
- 00:28:42okay for the eukaryotic cells
- 00:28:45what do we need we need the rna
- 00:28:47polymerase type 2. we said we're going
- 00:28:48to represent that with
- 00:28:50orange so here's going to be the rna
- 00:28:53polymerase
- 00:28:54type 2 and then what else do we need we
- 00:28:57need those
- 00:28:58general transcription factors there's a
- 00:29:00bunch of them but what's the particular
- 00:29:02one that i really want you to remember
- 00:29:04here
- 00:29:04transcription factor 2 d
- 00:29:08which contains the tata binding protein
- 00:29:10so it binds to the tata box which is the
- 00:29:12promoter region in the eukaryotic cells
- 00:29:14then allows the rna polymerase 2 to bind
- 00:29:17to the dna
- 00:29:18now once the rna polymerase is bound to
- 00:29:20the dna it's going to start
- 00:29:22moving down the dna strands reading it
- 00:29:25and making rna
- 00:29:26so we've now started the process of
- 00:29:28transcription that's all that's
- 00:29:29happening here
- 00:29:31the next step is that once we've bound
- 00:29:34had
- 00:29:34this rna so let's write these down here
- 00:29:36for the prokaryotic cell this would be
- 00:29:38the
- 00:29:38we'll put rna polymerase and we'll put h
- 00:29:42for the holoenzyme and for that one up
- 00:29:45here this is going to be
- 00:29:47rna polymerase type 2
- 00:29:50right once this is bound and it's in the
- 00:29:53dna it's going to start
- 00:29:54reading the dna as it reads the dna
- 00:29:58it'll make mrna that process by which it
- 00:30:01does that is called
- 00:30:03elongation so let's write that down now
- 00:30:06so the next step
- 00:30:07is elongation to make
- 00:30:11the mrna now within elongation a couple
- 00:30:16different things happens
- 00:30:18and this is thankfully the same in
- 00:30:20prokaryotic cells and eukaryotic
- 00:30:22cells so thank the lord for that right
- 00:30:23so let's just say that we take
- 00:30:25either one of these rna polymerases
- 00:30:27let's just for the heck of it we'll say
- 00:30:29here's your rna polymerase ii okay
- 00:30:33here's your rna polymerase two and it's
- 00:30:34reading the dna
- 00:30:36the dna we already know has two strands
- 00:30:39we're going to call this top strand here
- 00:30:42this top strand sonogram this top strand
- 00:30:44up here we're going to call this the
- 00:30:46template strand so the template strand
- 00:30:50also sometimes referred to as the
- 00:30:55anti-sense
- 00:30:57strand this strand down here we're going
- 00:30:59to call
- 00:31:00the coding strand
- 00:31:04now when rna polymerases read dna
- 00:31:07the strand that they read is the
- 00:31:10template strand or the antisense strand
- 00:31:13so that's the first thing i really need
- 00:31:15you guys to remember
- 00:31:16is that the rna polymerases
- 00:31:20what strand do they read they read
- 00:31:24we're going to put the template strand
- 00:31:27or also referred to as what else
- 00:31:30the antisense strand and that's the
- 00:31:32strand that they use to make the mrna
- 00:31:34they do not use the coding strand
- 00:31:37so let's kind of put a little asterisk
- 00:31:38here that this is the strand that we're
- 00:31:39gonna read
- 00:31:40now when it reads it it does it in a way
- 00:31:43that you guys if you guys watch our dna
- 00:31:44replication video this should be
- 00:31:46so darn easy let's say here
- 00:31:50this end of the dna is the three
- 00:31:53prime end that means that this end is
- 00:31:56the
- 00:31:57five prime end and remember one strand
- 00:32:00of dna
- 00:32:01on this side should have a complementary
- 00:32:04anti-parallel strand on the other side
- 00:32:06which means that this is the three and
- 00:32:08on here
- 00:32:08this has to be the five end on this side
- 00:32:11and this has to be the
- 00:32:13three end on that side what happens is
- 00:32:16this rna polymerase when it binds into
- 00:32:18the dna
- 00:32:19it does something very interesting it
- 00:32:21binds to the dna through the initiation
- 00:32:23process
- 00:32:23and then opens up the dna who opened up
- 00:32:27the dna before it was that whole
- 00:32:29in replication it was that whole like
- 00:32:30replication complex
- 00:32:32rna polymerase does that so the first
- 00:32:33thing we need to know is that rna
- 00:32:35polymerase does what
- 00:32:37it opens the dna
- 00:32:40now in replication what else happened
- 00:32:41you opened the dna and you had those
- 00:32:42single stranded binding proteins which
- 00:32:44keep it stable and kept it open right
- 00:32:46rna polymerase does that on its own so
- 00:32:48it also
- 00:32:49stabilizes the single
- 00:32:53stranded dna molecules right so it
- 00:32:55stabilizes the single strands
- 00:32:57then what was the enzyme in replication
- 00:33:00that opened up to unwound the dna
- 00:33:02helicase rna polymerase has its
- 00:33:05intrinsic helicase activity so it also
- 00:33:08unwinds the dna
- 00:33:12after it unwinds the dna then it starts
- 00:33:14reading the dna
- 00:33:15so let's say here as it reads the dna in
- 00:33:18this direction
- 00:33:19three to five it'll make mrna
- 00:33:24that'll be going in the opposite
- 00:33:26direction so it's going to read this 3
- 00:33:28all the way to the 5 direction and as it
- 00:33:31does that it starts synthesizing
- 00:33:33mrna right and this mrna
- 00:33:37will be synthesized in what direction
- 00:33:38what will this be this starting point
- 00:33:41the five end and what would be this
- 00:33:43point
- 00:33:44the three end so we know the next thing
- 00:33:46that the rna polymerase does
- 00:33:48whether it be in prokaryotic cells or
- 00:33:50eukaryotic cells
- 00:33:52is it reads the dna
- 00:33:55from three to five
- 00:33:58then it synthesizes
- 00:34:02rna from what direction guys
- 00:34:07five to three very
- 00:34:10very important the last thing that you
- 00:34:12guys should be asking is okay zach you
- 00:34:14also
- 00:34:15said that in replication the dna
- 00:34:18polymerases read the dna
- 00:34:20and then if there was an accident or a
- 00:34:22mistake they would proofread it and then
- 00:34:24cut out the nucleotide
- 00:34:25what about rna polymerases do they do
- 00:34:26that as well because it looks like
- 00:34:27they've done everything that was similar
- 00:34:29in dna replication
- 00:34:30that's the one thing that's
- 00:34:31controversial so the only thing that's
- 00:34:33kind of relatively controversial
- 00:34:35is is there a proof reading function we
- 00:34:38don't really know it's still subject to
- 00:34:39study
- 00:34:40so that's one thing to remember if you
- 00:34:42want to compare this
- 00:34:43the proofreading function is somewhat
- 00:34:46uncertain
- 00:34:47at this point in time all right so we
- 00:34:50have an idea now we've
- 00:34:51read this dna and we've made rna
- 00:34:54i know we talked about this a lot in dna
- 00:34:56replication we're talking about it here
- 00:34:58and sometimes it really can be confusing
- 00:35:00when you're saying
- 00:35:01five end three and i don't i don't i
- 00:35:03don't freaking get what you're talking
- 00:35:04about zach
- 00:35:04so i want to take a quick little second
- 00:35:06and explain what the heck i mean when i
- 00:35:08say it reads it from three
- 00:35:09to five and synthesizes it from five to
- 00:35:11three a diagram i really think will
- 00:35:13clear this up for you
- 00:35:14let's take a second to understand what i
- 00:35:16mean by reading the dna three to five
- 00:35:18and then
- 00:35:19synthesizing it five to three i think
- 00:35:20it's really important to understand that
- 00:35:22so let's say here we have this strand of
- 00:35:25dna so this is
- 00:35:26this is going to be our dna
- 00:35:30template if you will
- 00:35:33okay so this is our dna template on this
- 00:35:35side the blue one
- 00:35:36and then this is going to be the rna
- 00:35:39that we're going to synthesize utilizing
- 00:35:41the rna polymerase type 2 and eukaryotes
- 00:35:43are the rna polymerase hollow enzyme and
- 00:35:44prokaryotes
- 00:35:46now when we're making this rna we have
- 00:35:48to read
- 00:35:49the dna in what direction the three end
- 00:35:52to the five and what is the three and
- 00:35:54you guys remember the video on dna
- 00:35:55structure
- 00:35:56it's the oh so this is going to be the
- 00:35:59three end
- 00:35:59what's the five end it's the phosphate
- 00:36:02group
- 00:36:02so the phosphate group is going to be
- 00:36:04the five and so i have to read this
- 00:36:06starting at the o h portion towards the
- 00:36:09five end where the phosphate is so the
- 00:36:13rna polymerase let's pretend i'm the rna
- 00:36:15polymerase i'm walking right
- 00:36:16to do i find the three prime and i'm
- 00:36:18like oh there it is okay i'm gonna move
- 00:36:20up oh i found the
- 00:36:21three prime five prime let me just fill
- 00:36:22this up oh i feel my nitrogenous base
- 00:36:25the nitrogenous base that it feels is
- 00:36:27adenine so it picks into its little
- 00:36:29satchel of nucleotides it's like okay
- 00:36:31this is adenine
- 00:36:32the complementary base for is thymine uh
- 00:36:35oh no that's not correct because you
- 00:36:37guys know
- 00:36:38that if we're taking dna making rna
- 00:36:41what's the one nucleotide that
- 00:36:42switches from dna and rna adenine is no
- 00:36:46longer complementary to thymine
- 00:36:48in the rna it is uracil
- 00:36:52so the dna the rna polymerase will come
- 00:36:54read find the three end
- 00:36:56read the nucleotide and say oop okay
- 00:36:58this is an adenine
- 00:36:59reach into its satchel of a bunch of
- 00:37:01nucleotides and pull out
- 00:37:03uracil when it pulls that out it then
- 00:37:06puts the nucleotide in a particular
- 00:37:08orientation
- 00:37:10what's the orientation we said it reads
- 00:37:11it from three to five
- 00:37:13and synthesizes it from five to three
- 00:37:15what's the five
- 00:37:16end here's the nucleotide the five end
- 00:37:19is this
- 00:37:19phosphate group the three end
- 00:37:22is this oh group so it's going to kind
- 00:37:24of flip the nucleotide the opposite
- 00:37:27direction
- 00:37:28and make sure that the nitrogenous base
- 00:37:30here is what
- 00:37:31uracil then when it does that it's going
- 00:37:34to go to the next one so it's going to
- 00:37:35continue it's going to go to the next
- 00:37:36point
- 00:37:37here's where the next oh group would be
- 00:37:38right the three prime end
- 00:37:40reads it finds that finds the nucleotide
- 00:37:42it says oh the nitrogenous base here is
- 00:37:45t let me reach into my satchel of a
- 00:37:47bunch of different uh
- 00:37:49good old nucleotides i'm going to read
- 00:37:50it t goes with a
- 00:37:52i'm going to put my nucleotide and i'm
- 00:37:53going to flip it where it's five prime
- 00:37:55end
- 00:37:56going down three prime end pointing up
- 00:37:59and then the nitrogenous base which is
- 00:38:02complementary to the t
- 00:38:03is a when it does that
- 00:38:06it then fuses the three prime end
- 00:38:10and the five prime end together making a
- 00:38:13bond what is that bond called
- 00:38:14the phosphodiester bond and the same
- 00:38:17process occurs
- 00:38:18so then it'll do what let's fix this
- 00:38:21three prime in there
- 00:38:22it'll then go go to the next nucleotide
- 00:38:24here's the three prime end where the oh
- 00:38:26group is
- 00:38:26reads it finds the nucleotide says that
- 00:38:29it's a g reaches into its satchel pulls
- 00:38:31out a nucleotide
- 00:38:32with the cytosine when it does it it
- 00:38:34flips it to where the five
- 00:38:35end is on this side there's my phosphate
- 00:38:38the three prime end is upwards
- 00:38:40and it says oh the nucleotide that goes
- 00:38:42with this
- 00:38:43is with the nitrogenous base c then it
- 00:38:46says oh
- 00:38:46i have my phi prime n situated close to
- 00:38:49the three prime end of the preceding
- 00:38:51nucleotide
- 00:38:52let me fuse these two together and make
- 00:38:54my phosphate ester bond
- 00:38:56and just for the heck of it because
- 00:38:57repet repetition i guess is helpful
- 00:38:59we go reads this says okay next one
- 00:39:02here's my three prime end where the oh
- 00:39:03group is
- 00:39:04read it find the nitrogenous base it's a
- 00:39:06cytosine
- 00:39:09digs into its satchel pulls out the
- 00:39:10nucleotide guanosine
- 00:39:13sorry the guanine nitrogenous base then
- 00:39:15when it does that
- 00:39:16it situates it where the five prime end
- 00:39:19is situated down
- 00:39:21three prime n is situated upwards in
- 00:39:22this case and then
- 00:39:24the nitrogenous bases on guanine
- 00:39:28then it says oh my five prime n i can
- 00:39:30stitch it to the three prime end of the
- 00:39:32preceding nucleotide
- 00:39:33and form my phosphodiester bond and
- 00:39:35that's how we make rna
- 00:39:37reading it three to five and
- 00:39:40synthesizing it from five to
- 00:39:42three dang we good all right
- 00:39:45now that we've done that the last thing
- 00:39:47i need you to understand is that
- 00:39:48rna polymerase is a very important
- 00:39:50enzyme within eukaryotic and prokaryotic
- 00:39:52cells
- 00:39:54a question that can come up and it's so
- 00:39:56dumb and annoying but you should know it
- 00:39:59is that in eukaryotic cells
- 00:40:02we can inhibit the rna polymerase
- 00:40:06by using a kind of toxin amanitin it's
- 00:40:10for mushrooms
- 00:40:11and this can inhibit the rna polymerase
- 00:40:14within we'll put eukaryotic cells
- 00:40:18okay there's another drug
- 00:40:21which they love to ask in the exams as
- 00:40:23well called rifampicin it's an
- 00:40:24antibiotic
- 00:40:27and this inhibits the rna polymerase
- 00:40:31within if it's an antibiotic that's good
- 00:40:33against bacteria prokaryotic cells
- 00:40:35so this will inhibit the rna polymerase
- 00:40:37within prokaryotic cells
- 00:40:39which would inhibit what the part of the
- 00:40:42initiation
- 00:40:43the elongation basically making rna if
- 00:40:45you can't make rna you can't make
- 00:40:46proteins
- 00:40:47if you can't make proteins you can't
- 00:40:48perform the general functions of the
- 00:40:50cell
- 00:40:51so this is kind of from a poisonous
- 00:40:54mushroom which is stupid to know that
- 00:40:55but they like to ask it on your exams
- 00:40:57and then rifampicin is an antibiotic
- 00:40:58which they also love to ask
- 00:41:00okay now we've talked about elongation
- 00:41:03we've made the dang rna
- 00:41:05rna polymerase is working real hard the
- 00:41:08last thing we got to do is we got to
- 00:41:09just
- 00:41:09end it we don't need any more rna we've
- 00:41:11made the rna that we need to make the
- 00:41:12protein
- 00:41:13that is called termination all right so
- 00:41:16we talked about elongation the next step
- 00:41:18the last step really that we got to
- 00:41:20discuss here is
- 00:41:21termination we've got to end this whole
- 00:41:23transcription process so the last step
- 00:41:25is
- 00:41:25termination now unfortunately
- 00:41:27termination is probably one of the more
- 00:41:29annoying and complicated ones
- 00:41:31unfortunately
- 00:41:32and it is different in prokaryotes and
- 00:41:34eukaryotes that's why it kind of makes
- 00:41:35it a little bit frustrating
- 00:41:37but termination is basically where we've
- 00:41:40already made our rna transcript and we
- 00:41:43just need to
- 00:41:44detach it or disassociate it away from
- 00:41:46the dna and
- 00:41:47prevent that rna polymerase from reading
- 00:41:50any more of the dna and making any more
- 00:41:51rna so just stop
- 00:41:52transcription how do we do that in
- 00:41:55prokaryotes there's two mechanisms
- 00:41:58one of the ways that this happens is
- 00:42:00through what's called
- 00:42:02road dependent termination so one is via
- 00:42:04this process called row
- 00:42:07dependent termination and it's really
- 00:42:10simple believe it or not
- 00:42:12so let's say here we take the
- 00:42:13prokaryotics we we picked blue for our
- 00:42:16rna polymerase so the rna polymerase
- 00:42:18here's our rna polymerase
- 00:42:20it's reading this dna as it's reading
- 00:42:23the dna again what is it making from it
- 00:42:26you guys remember it's making the rna in
- 00:42:29this case
- 00:42:30it could be any rna it could be the mrna
- 00:42:32trna rna whatever
- 00:42:35as it does this there's a protein called
- 00:42:37rho
- 00:42:38and what rho does is this rho protein
- 00:42:42will start moving up the mrna
- 00:42:45and as it moves up the rna that's being
- 00:42:47synthesized by the rna polymerase as it
- 00:42:49gets to this rna polymerase it basically
- 00:42:53says hey
- 00:42:54it just punches the rna polymerase off
- 00:42:56the dna
- 00:42:58if you punch the rna polymerase off the
- 00:43:01dna
- 00:43:02is it going to be able to continue to
- 00:43:03keep breeding the dna and making
- 00:43:05any more rna no so that terminates the
- 00:43:08transcription process
- 00:43:10so the big thing i need you guys to know
- 00:43:11here is that with the road dependent
- 00:43:13termination
- 00:43:14is rho protein
- 00:43:17causes rna polymerase
- 00:43:21uh to break away to disassociate if you
- 00:43:25will
- 00:43:25okay to break
- 00:43:29away from the dna okay
- 00:43:32all right beautiful the next mechanism
- 00:43:35within prokaryotes
- 00:43:37is rho independent termination so we
- 00:43:40don't use the row protein
- 00:43:41so we call this row
- 00:43:45independent termination now with this
- 00:43:48process it's a little bit more
- 00:43:49complicated and a little annoying
- 00:43:52let's say here we have the dna right and
- 00:43:54within the dna we're going to mark these
- 00:43:56here we're going to say this is our
- 00:43:57template strand right so this strand is
- 00:43:59the template strand
- 00:44:01right or the antisense strand and then
- 00:44:03this is going to be our coding strand
- 00:44:05so which one does the rna polymerase
- 00:44:08read it reads the
- 00:44:09template strand or the antisense strand
- 00:44:12there's a particular like thing called
- 00:44:14inverted repeats that form within the
- 00:44:17dna that the rna polymerase is reading
- 00:44:20so what happens is this rna polymerase
- 00:44:22will bind
- 00:44:23to that template strand and it'll start
- 00:44:25reading it
- 00:44:26making the rna as it starts making this
- 00:44:29rna
- 00:44:30it it encounters a particular sequence
- 00:44:33of
- 00:44:34of dna called inverted repeats let's
- 00:44:37write these inverted repeats out in kind
- 00:44:38of a nice little color let's do let's do
- 00:44:40orange
- 00:44:42and let's say here we have an inverted
- 00:44:43repeat where we have c
- 00:44:45c g g and then a bunch of nucleotides
- 00:44:48that we don't care about
- 00:44:50and then here we'll have ggcc
- 00:44:55okay then we're just going to have this
- 00:44:57is the template again
- 00:44:58on the coding strain it would just be
- 00:45:00the complementary base so if this was cc
- 00:45:02this would be gg
- 00:45:04cc we don't really care about these
- 00:45:06nucleotides cc
- 00:45:08gg right the rna polymerase is going to
- 00:45:11read this template strand what happens
- 00:45:13is right you're going to get this kind
- 00:45:15of strand here where you'll have
- 00:45:17a bunch of nucleotides already kind of
- 00:45:18made up here
- 00:45:20and then it reaches this kind of like
- 00:45:21inverted repeat area
- 00:45:23and what happens is it reads this and
- 00:45:25then basically everything you read
- 00:45:27within the template strand should be the
- 00:45:28same as it is in the coding strand
- 00:45:30because it's the complementary base
- 00:45:31so you'll have g g c
- 00:45:34c that it'll make a bunch of nucleotides
- 00:45:36we don't care about
- 00:45:37and then c c g g
- 00:45:41what happens is whenever this
- 00:45:44rna is kind of coming and being
- 00:45:46transcribed from the rna polymerase
- 00:45:48something interesting happens where some
- 00:45:50of these c's and some of these g's on
- 00:45:53this portion have a strong affinity for
- 00:45:56some of the c's and some of the g's
- 00:45:58in this portion of the rna and as they
- 00:46:01start having this affinity they start
- 00:46:02approaching and kind of wanting to
- 00:46:04interact with one another via these
- 00:46:05hydrogen bonds
- 00:46:07and so it creates this really
- 00:46:09interesting kind of like hairpin loop if
- 00:46:11you will
- 00:46:12where there's a bunch of g's and c's
- 00:46:15within this kind of hairpin loop
- 00:46:19that are kind of interacting with one
- 00:46:21another and what happens
- 00:46:23is that hairpin loop is what
- 00:46:26triggers the rna polymerase to pretty
- 00:46:29much
- 00:46:30hop off of the dna and terminate the
- 00:46:32transcription process
- 00:46:34because what happens is once you form
- 00:46:35this hairpin loop what will happen is
- 00:46:37there's going to be particular enzymes
- 00:46:39that will
- 00:46:39bind to that portion and cleave the d
- 00:46:42the rna
- 00:46:43away from the rna polymerase so the big
- 00:46:46thing i need you to
- 00:46:47know within row independent termination
- 00:46:50is that you'll hit this area the rna
- 00:46:51polymerase will be transcribing
- 00:46:53reading the dna making rna it'll hit
- 00:46:55these areas of inverted repeats
- 00:46:58when these inverted repeats are made
- 00:47:00they create this thing called a
- 00:47:03hairpin loop this hairpin loop
- 00:47:07will then trigger particular cleavage
- 00:47:10enzymes
- 00:47:11to come and cleave a couple nucleotides
- 00:47:15after that hairpin loop
- 00:47:16to cleave that away from the rna
- 00:47:19polymerase
- 00:47:20and then here you have your rna that you
- 00:47:23formed
- 00:47:24so that is one of the ways that we have
- 00:47:25termination road
- 00:47:27independent via prokaryotes the last
- 00:47:30termination mechanism is going to be
- 00:47:32eukaryotic cells now how does this work
- 00:47:36this one's actually relatively simple so
- 00:47:38we had the rna polymerase in eukaryotes
- 00:47:40and this was orange
- 00:47:42okay it's binding to the dna it's
- 00:47:44reading the dna
- 00:47:45as it's reading the dna it's making rna
- 00:47:50as it starts making this rna it hits a
- 00:47:52particular sequence
- 00:47:54where when it starts reading the dna and
- 00:47:56makes rna
- 00:47:58it makes a particular sequence of
- 00:48:01a a u a a
- 00:48:04a okay so what are the what is the
- 00:48:06nucleotide sequence here let's write it
- 00:48:08out
- 00:48:08this portion here will be double a u
- 00:48:11triple a this is what's called a
- 00:48:14polyadenylation signal
- 00:48:16so what is this called here this is
- 00:48:18called a poly
- 00:48:19adenylation signal
- 00:48:24and once this kind of nucleotide
- 00:48:27sequence occurs
- 00:48:28so it's kind of now that we know what
- 00:48:29that nucleotide sequence is let's kind
- 00:48:30of just put like this
- 00:48:33here's that nucleotide sequence that
- 00:48:34polyadenylation signal
- 00:48:36that's been synthesized or formed by the
- 00:48:38rna polymerase with the eukaryotes
- 00:48:40once that happens it activates
- 00:48:42particular
- 00:48:43enzymes and those enzymes will come to
- 00:48:46the area here
- 00:48:49and cleave the rna away from the rna
- 00:48:52polymerase
- 00:48:53separating out this rna away
- 00:48:58from the dna and the rna polymerase and
- 00:49:00then again what will i have at this
- 00:49:01portion here
- 00:49:02just as kind of a diagrammatic portion
- 00:49:05here this will be my
- 00:49:06polyadenylation signal this is important
- 00:49:09because we're going to talk about
- 00:49:10post-transcriptional modification in a
- 00:49:11second
- 00:49:12so i know this was a lot of crap just
- 00:49:14really quickly
- 00:49:15recap because this is one of the
- 00:49:16toughest parts of transcription
- 00:49:18is termination prokaryotes there's two
- 00:49:20ways road dependent row independent
- 00:49:23with this one you need a row protein to
- 00:49:25knock the rna polymerase off if you
- 00:49:26don't have him he can't make any more
- 00:49:28rna
- 00:49:29the other one is row independent you
- 00:49:30don't have a row protein
- 00:49:32the rna polymerase is reading the dna
- 00:49:34making rna and it hits these areas of
- 00:49:37inverted repeats these inverted repeats
- 00:49:40when they're made within the
- 00:49:41rna it creates a hydrogen bond
- 00:49:44interaction between them
- 00:49:46which causes it to loop forming a
- 00:49:47hairpin loop that
- 00:49:49signals particular enzymes to break the
- 00:49:52rna
- 00:49:53away from the rna polymerase and we've
- 00:49:55made our rna there
- 00:49:56the last one is in eukaryotes the rna
- 00:49:59polymerase is reading the dna
- 00:50:01and it reaches a particular sequence of
- 00:50:02nucleotides where it reads
- 00:50:04and then makes a a u
- 00:50:08triple a a polyadenylation signal which
- 00:50:11activates enzymes to come
- 00:50:12cleave the rna away from the rna
- 00:50:14polymerase terminating
- 00:50:16the transcription process that really
- 00:50:19hammers this home let's now talk about
- 00:50:21post-transcriptional modification
- 00:50:22we know at this point how to take dna
- 00:50:25make rna
- 00:50:26right we talked about all the different
- 00:50:27types of rna utilizing rna polymerases
- 00:50:29utilizing the transcription factors we
- 00:50:30talked a little about a gene regulation
- 00:50:32we even went through all the stages of
- 00:50:34transcription
- 00:50:36taking the dna and making the mrna
- 00:50:39all the way up until the point where we
- 00:50:41finally made the mrna and broken it away
- 00:50:44from the dna
- 00:50:45unfortunately that's not it for
- 00:50:47transcription
- 00:50:48now we have this mrna right so we
- 00:50:51basically what have we covered up to
- 00:50:53this point
- 00:50:54we took the dna
- 00:50:57we read let's just say here
- 00:51:01at this portion i'll just put here's our
- 00:51:03promoter
- 00:51:04our rna polymerase has read this gene
- 00:51:06sequence
- 00:51:08we hit a termination sequence let's say
- 00:51:10here's our termination sequence
- 00:51:12that we talked about here and once we
- 00:51:15hit that termination sequence
- 00:51:17the rna polymerase will fall off and
- 00:51:19then from this you'll make the
- 00:51:21rna so this was pretty much the basic
- 00:51:23aspects of the transcription
- 00:51:26but now we got to modify this now here's
- 00:51:28the thing
- 00:51:30it's actually kind of a misnomer to say
- 00:51:32that this
- 00:51:33is mrna it's technically not mrna right
- 00:51:37now
- 00:51:37so this piece of rna that we made okay
- 00:51:41and this is this process of
- 00:51:42post-transcriptional modification
- 00:51:44this only occurs it's very important let
- 00:51:46me actually write this down
- 00:51:47this only occurs in
- 00:51:50eukaryotic cells so that's nice
- 00:51:53all this stuff that we're going to talk
- 00:51:54about here is only in eukaryotic cells
- 00:51:56it doesn't happen in prokaryotic cells
- 00:51:57so they just make their rna and that's
- 00:51:59it so technically
- 00:52:01this immature mrna if you will we
- 00:52:03actually give it a very specific name we
- 00:52:05call it heterogeneous
- 00:52:07nuclear rna now
- 00:52:10this heterogeneous nuclear rna is kind
- 00:52:12of an immature
- 00:52:14mrna that has to go through some
- 00:52:15modifications to really make mature
- 00:52:18mrna that then can be translated to make
- 00:52:20proteins
- 00:52:21what are those modifications the first
- 00:52:24thing that we have to do
- 00:52:26is we have to put something on one of
- 00:52:29these ends so now we got to know a
- 00:52:30little bit about the
- 00:52:31terminology of the ends of this immature
- 00:52:35mrna or hn rna on this end
- 00:52:38we're going to call this the five prime
- 00:52:41end what's on that five prime end do you
- 00:52:42guys remember
- 00:52:43the phosphate groups what's on this end
- 00:52:46the three prime end what's on the three
- 00:52:47prime mint
- 00:52:48the oh group okay now
- 00:52:51something very interesting is on the
- 00:52:52five prime end on the five prime end of
- 00:52:55this heterogeneous nuclear rna or the
- 00:52:57hrna
- 00:52:58you have a triphosphate which we're
- 00:53:00representing here with these
- 00:53:02orange circles an enzyme
- 00:53:05comes to the rescue and cleaves off
- 00:53:09one of those phosphate molecules what is
- 00:53:11that enzyme called
- 00:53:12it's this orange little cute enzyme this
- 00:53:15orange enzyme is called
- 00:53:17rna tri-phosphatase
- 00:53:23and what it does is it comes and cleaves
- 00:53:26off
- 00:53:27what portion it cleaves off one of these
- 00:53:31phosphate groups it's going to cleave
- 00:53:33off one of the phosphate groups
- 00:53:34so now i only have two phosphates on the
- 00:53:37end
- 00:53:38of this five prime end then another
- 00:53:41enzyme comes in
- 00:53:42and it says hey there's only two
- 00:53:44phosphates here
- 00:53:45i can now add something on here and i'm
- 00:53:49going to add on what's called a
- 00:53:52gmp molecule what am i going to add on
- 00:53:54again
- 00:53:55i'm going to add a gmp molecule which is
- 00:53:58guanosine monophosphate so we're going
- 00:54:01to represent that here which
- 00:54:03we add on the phosphate for the
- 00:54:05guanosine monophosphate
- 00:54:07and then we're going to just represent
- 00:54:08this as the guanosine so this is our
- 00:54:10guanosine and that blue circle there is
- 00:54:12the phosphate on the guanosine
- 00:54:14so what does he add on technically
- 00:54:17he adds on to this little two phosphates
- 00:54:20right
- 00:54:21it adds in gtp but
- 00:54:24when it does that two phosphates are
- 00:54:27released
- 00:54:28in the form of pyrophosphate which then
- 00:54:31get broken down by pyrophosphatase into
- 00:54:34individual phosphates so if i took gtp
- 00:54:37and i removed two phosphates what am i
- 00:54:39left with
- 00:54:40gmp so it adds on this gmp group
- 00:54:43onto that two phosphate end on the five
- 00:54:46prime end
- 00:54:47so this enzyme that adds that gmp on in
- 00:54:50the form of gtp is called
- 00:54:52guanolile
- 00:54:55uh transferase
- 00:54:58guanalyl transferase beautiful
- 00:55:02so this last enzyme here which is
- 00:55:03involved in this step here on the five
- 00:55:05prime n
- 00:55:06is going to add on a methyl group onto
- 00:55:09one of the
- 00:55:10components of the guanosine
- 00:55:11monophosphate it's actually like one of
- 00:55:14the seventh
- 00:55:14components on that structure it adds on
- 00:55:17a methyl group
- 00:55:19and so at the end of this this enzyme
- 00:55:23which adds a methyl group on what do you
- 00:55:24think it's called methyltransferase
- 00:55:30at the end of this process where you
- 00:55:32took the prime end which had three
- 00:55:33phosphates got rid of one
- 00:55:36took the guanola transfers added on the
- 00:55:37gmp took the methyl transferase added on
- 00:55:40that methyl group
- 00:55:41you formed this complex here and we call
- 00:55:43this whole complex that we just added on
- 00:55:46a seven methyl guanosine group
- 00:55:49okay and that's on that five prime end
- 00:55:53this is called capping
- 00:55:57this is called capping so whatever we've
- 00:55:59just done on this
- 00:56:00five prime end is called capping what
- 00:56:03the heck do we do all this stuff for
- 00:56:05the whole purpose of capping
- 00:56:08is to help to initiate
- 00:56:13translation so this sequence this kind
- 00:56:15of five prime end
- 00:56:16with that seven methyl guanosine or that
- 00:56:18five prime capping if you will
- 00:56:21it's kind of a signal sequence if you
- 00:56:23will that allow for it to interact with
- 00:56:25the ribosome
- 00:56:26and undergo translation the other thing
- 00:56:28it does is it
- 00:56:30prevents degradation by
- 00:56:33nuclease enzymes that want to come and
- 00:56:35break down
- 00:56:36the rna so it helps to prevent
- 00:56:38degradation helps to initiate the
- 00:56:40translation process
- 00:56:43one more thing that they it's a dumb
- 00:56:45thing to know but they love to ask it
- 00:56:47is that there is a particular molecule
- 00:56:51that this methyltransferase
- 00:56:52uses to add that methyl group on and
- 00:56:55sometimes it's really important to know
- 00:56:56it
- 00:56:57and this is called s adenosyl methionine
- 00:57:00also known as
- 00:57:01sam sam carries a methyl group it's like
- 00:57:04a methyl donor if you will
- 00:57:06it gives that methyl group to the methyl
- 00:57:09transferase
- 00:57:10and the methyl transferase adds that
- 00:57:12methyl group onto the guanosine
- 00:57:13monophosphate forming the
- 00:57:157-methylguanosine
- 00:57:17or that 5-prime cap okay
- 00:57:20so that's the first thing that happens
- 00:57:22now we got to talk about the 3-prime end
- 00:57:24on the three prime end we had that oh
- 00:57:26group right that's the ohn but do you
- 00:57:28remember
- 00:57:30in eukaryote there was a particular
- 00:57:32signal
- 00:57:33that prevent that generated that
- 00:57:36terminated transcription what was that
- 00:57:38nucleotide signal do you guys remember
- 00:57:40test your knowledge guys
- 00:57:42a a u
- 00:57:45triple a right that was that
- 00:57:47polyadenylation signal do you guys
- 00:57:49remember that the polyadenylation
- 00:57:50segment we talked about in eukaryotes
- 00:57:53that polyadenylation signal is
- 00:57:55recognizable
- 00:57:56by this cute little purple enzyme here
- 00:57:59this cute little purple enzyme is called
- 00:58:01poly a
- 00:58:04polymerase it's called
- 00:58:08poly a polymerase what it does is on
- 00:58:11this
- 00:58:11hand it has a bunch of
- 00:58:15adenine
- 00:58:19nucleotides right so it can eat a lot of
- 00:58:21nucleotides containing the adenine
- 00:58:22nitrogenous base
- 00:58:24it takes one end and identifies that
- 00:58:27polyadenylation signal
- 00:58:28takes the other end and adds on
- 00:58:32all of those adenine nucleotides a bunch
- 00:58:37of them
- 00:58:37sometimes up to 200 adenine nucleotides
- 00:58:41when it does that this forms a tail
- 00:58:44on that three prime end with a bunch of
- 00:58:47adenine nucleotides and we call this the
- 00:58:50poly a tail
- 00:58:54so the poly a tail what's the purpose of
- 00:58:58this
- 00:58:58it's the exact same thing helps to
- 00:59:01initiate
- 00:59:02the translation process
- 00:59:06and helps to decrease degradation
- 00:59:10by what kind of enzymes nucleases that
- 00:59:13will try to come and break down that end
- 00:59:15okay the other thing that they do is
- 00:59:17they help transport this
- 00:59:20hn rna eventually they're going to help
- 00:59:22to transport the
- 00:59:24hnrna which will become mrna out of the
- 00:59:26nucleus into the cytosol so they also
- 00:59:28play a little bit of a role in
- 00:59:29transport out of the nucleus and into
- 00:59:32the cytosol
- 00:59:34okay so within this first step what did
- 00:59:37we do
- 00:59:38we did five prime capping we went over
- 00:59:40that part and the three prime
- 00:59:42poly a tail that we did okay now we have
- 00:59:46this so after we did all of this massive
- 00:59:48mess
- 00:59:49we've come to this point
- 00:59:53okay on this part what do we have
- 00:59:57we're just going to write these we're
- 00:59:58going to circle it here this is our
- 01:00:00five prime cap with the
- 01:00:017-methylguanosine
- 01:00:03and on this end we already have kind of
- 01:00:05formed our
- 01:00:07polyetail the next thing that happens is
- 01:00:11what's called
- 01:00:12splicing and this can be sometimes a
- 01:00:14little annoying
- 01:00:15but it's not too bad i promise let's say
- 01:00:19here
- 01:00:20this is the sequence of nucleotides
- 01:00:22within this
- 01:00:23rna okay we're not at mrna yet we're
- 01:00:27still at this h in rna we're still kind
- 01:00:29of at this h
- 01:00:30in rna at this point we haven't made
- 01:00:32mrna yet
- 01:00:34within this hn rna there's particular
- 01:00:37nucleotides that will be read translated
- 01:00:41and actually will code for particular
- 01:00:43amino acids
- 01:00:45there's other nucleotides within this h
- 01:00:48rna
- 01:00:48that will not be read and they do not
- 01:00:51code for a particular amino acid
- 01:00:53we give those very specific names i'm
- 01:00:56going to highlight them
- 01:00:57in different colors so let's say i
- 01:01:00highlight this one here
- 01:01:02and pink and then i will highlight
- 01:01:05this one here in this kind of maroon
- 01:01:07color
- 01:01:09and then i'll pick here a blue
- 01:01:13and then we'll do another maroon color
- 01:01:14and then we'll do one more color after
- 01:01:16this here's another maroon
- 01:01:18and then we will do just for the heck of
- 01:01:21it black
- 01:01:23okay these portions here
- 01:01:27the pink one this is actually going to
- 01:01:29code
- 01:01:30for an amino acid if it codes for an
- 01:01:33amino acid we give a very specific name
- 01:01:35for that
- 01:01:36and we call it exons so exons
- 01:01:39code for an amino acid
- 01:01:43okay particularly amino acids will make
- 01:01:46proteins
- 01:01:47these other portions and again that's
- 01:01:49going to be or we'll
- 01:01:51i'll mention which ones are exons and
- 01:01:52which ones are the next thing which is
- 01:01:54called
- 01:01:54introns introns are basically
- 01:01:57nucleotide sequences that
- 01:02:01do not code
- 01:02:05for amino acids which will help to make
- 01:02:08proteins
- 01:02:09very important i'm going to call this
- 01:02:12pink portion of the h and rna
- 01:02:15i'm going to call this an exon but we
- 01:02:16have a bunch of them in this h and rna
- 01:02:18so i'm going to call this exon one
- 01:02:20okay that's going to code for some amino
- 01:02:22acids
- 01:02:24i'm going to have this portion here
- 01:02:25which is going to be in the maroon i'm
- 01:02:26going to call this
- 01:02:27an intron but you can have multiple
- 01:02:29introns so i'm going to call this intron
- 01:02:311.
- 01:02:32same thing here this is going to be
- 01:02:34coding
- 01:02:35so if it codes it's what it's an exon
- 01:02:38well we have multiple types so we're
- 01:02:39going to call this exon 2.
- 01:02:42then i'm going to test you again this
- 01:02:44one does not code for amino acids
- 01:02:46so this is going to be a intron but we
- 01:02:49have already intron once we're going to
- 01:02:50call this
- 01:02:51intron 2 and you guys already kind of
- 01:02:52get the the pattern that i'm going with
- 01:02:54here
- 01:02:55this one does code so it's going to be a
- 01:02:58exon
- 01:02:59and we already have 1 2 so this will be
- 01:03:01three
- 01:03:02okay we're going to do something called
- 01:03:05splicing
- 01:03:06where let's think about this if the
- 01:03:09introns don't
- 01:03:10code for any amino acids do we even need
- 01:03:12them
- 01:03:13no let's get rid of them that's all that
- 01:03:15splicing is
- 01:03:16it's getting rid of these introns or
- 01:03:18also known as intervening sequences
- 01:03:21and then stitching together the exons
- 01:03:25now in order for that process to occur
- 01:03:29we need very specific molecules and we
- 01:03:32talked about it before
- 01:03:33let's see if you guys remember him rna
- 01:03:36polymerase two and three they made
- 01:03:38another very interesting small little
- 01:03:39rna what was that rna called
- 01:03:42small nuclear rna right
- 01:03:45original right so small nuclear rna
- 01:03:48is gonna combine we haven't used this
- 01:03:50color yet so let's add this
- 01:03:53these brown proteins okay so you're
- 01:03:56gonna have some proteins
- 01:03:57and some small nuclear rna together
- 01:04:01these two things make up a very weird
- 01:04:04name
- 01:04:05called a snurp
- 01:04:08okay snurps small nuclear
- 01:04:12ribo ribonuclear proteins so our small
- 01:04:14nuclear ribonuclear proteins and what
- 01:04:16they do
- 01:04:16is these snurps are going to bind
- 01:04:21to this hn rna and they're going to
- 01:04:24cleave
- 01:04:25out the introns in this this actual rna
- 01:04:29and then they're going to stitch
- 01:04:30together the exons
- 01:04:32so let's show that in a very basic way
- 01:04:34of how that happens
- 01:04:35so these snares which are the snra and
- 01:04:38your proteins
- 01:04:40are going to perform splicing so what
- 01:04:44would that look like let's let's take
- 01:04:45here
- 01:04:47our transcript here and bring it down
- 01:04:49here all the way down
- 01:04:50to this portion here
- 01:04:54so here we're going to make our
- 01:04:55functional mrna so at this point in time
- 01:04:57we've actually made what
- 01:04:59at this point we've made the mature
- 01:05:02mrna and
- 01:05:05if i were to show kind of what was the
- 01:05:09end result what am i going to have here
- 01:05:11let's say here i have a sequence that's
- 01:05:12in pink that's exon one
- 01:05:15i got rid of intron one so what should
- 01:05:17be next
- 01:05:18i should have exon two
- 01:05:22i got rid of intron too so watch what
- 01:05:24should be left
- 01:05:25we're gonna expand it a little bit here
- 01:05:27get rid of that one
- 01:05:29exon three so all i did was i
- 01:05:33took and got rid of each exon i mean
- 01:05:36each
- 01:05:36in intron and stitch together
- 01:05:40only the exon so now let's show kind of
- 01:05:43coming out of this process here what am
- 01:05:45i going to have kind of
- 01:05:46popping out off of this the introns
- 01:05:50and when the introns pop off this can be
- 01:05:53intron
- 01:05:56one and then you can have another one
- 01:05:59let's say intron two these are going to
- 01:06:02get popped off
- 01:06:04we don't need these dang things anymore
- 01:06:06so since we don't need them we're just
- 01:06:08going to spit them off during that
- 01:06:10splicing process and
- 01:06:11only lead to the formation of exons now
- 01:06:14within this
- 01:06:15mrna i have my five prime cap
- 01:06:18i have my poly a tail i have only the
- 01:06:22nucleotide sequence which is going to
- 01:06:23code for amino acids
- 01:06:25and then if you really want to go the
- 01:06:27extra mile we said this is the five
- 01:06:28prime in
- 01:06:29this is the three prime end i'm not
- 01:06:31representing any kind of like
- 01:06:33dashes here so this portion here
- 01:06:36and this portion here doesn't get
- 01:06:39translated or red at all by the
- 01:06:40ribosomes
- 01:06:41and so we call these regions since they
- 01:06:44don't get translated
- 01:06:45the five primes it's near the five prime
- 01:06:47untranslated region
- 01:06:49and this one doesn't get translated so
- 01:06:50it's called the three prime
- 01:06:52untranslated region the only portion
- 01:06:54that gets translated is the
- 01:06:56axons now
- 01:06:59i don't know why but they love to ask
- 01:07:02this stuff
- 01:07:02in your exams where you actually go
- 01:07:05through the specific mechanism
- 01:07:07of how the snurps truly do pull the
- 01:07:10n-trons out and splice together the
- 01:07:12axons
- 01:07:13so let's say we take just exon one
- 01:07:17let's write this one as exon one
- 01:07:21and this one is going to be exon two
- 01:07:25and then here in the middle we're going
- 01:07:27to make this
- 01:07:31intron 1.
- 01:07:34so let's kind of show you how these
- 01:07:36snurps
- 01:07:37again the snurps which is the s rna and
- 01:07:40the proteins do this
- 01:07:41so if you really wanted to show it let's
- 01:07:43just represent the snurps as kind of a
- 01:07:45black blob if you will
- 01:07:46they're going to kind of bind
- 01:07:50near this portion here so here's my
- 01:07:51snurp
- 01:07:54within this portion here right at the
- 01:07:56intron at this portion
- 01:07:58let's say here is the three prime end of
- 01:08:00this exon
- 01:08:01five prime end of this exon and let's
- 01:08:04say that here is going to be the five
- 01:08:05prime end of exon two and then the three
- 01:08:09prime end
- 01:08:10of exon two okay and then here's going
- 01:08:13to be the intron inside
- 01:08:16within this intron you have a very
- 01:08:18specific nucleotide sequence that's near
- 01:08:20the
- 01:08:20three prime splice site near exon 1
- 01:08:24and the beginning of intron 1 and then
- 01:08:26you have a very specific nucleotide
- 01:08:28sequence near the 5
- 01:08:29prime splice site at exon 2 and at the
- 01:08:32end of intron 1.
- 01:08:33what are that nucleotide sequence it's
- 01:08:36dumb
- 01:08:36but it helps me to remember it so i say
- 01:08:39i'm a g
- 01:08:40how about you i'm a g so you remember
- 01:08:43g u i'm a g how about you
- 01:08:47i'm a g that's the basic way that i
- 01:08:50remember the nucleotide sequence at the
- 01:08:52three prime splice site
- 01:08:54and then the one at the five prime
- 01:08:56supply site between exon one exon two
- 01:08:58and intron one in this example
- 01:09:01at the there's another one right smack
- 01:09:03dab in the middle let's make him a
- 01:09:04different color so we don't confuse
- 01:09:06it smack dab in the middle there's a
- 01:09:08branch point which is an
- 01:09:10adenine okay there's an adenine right at
- 01:09:12this branch point
- 01:09:14and it has a very specific oh group kind
- 01:09:16of hanging from it
- 01:09:18okay so this is called your branch point
- 01:09:21what happens is is the snurps will come
- 01:09:24in
- 01:09:26and they're gonna cleave at that three
- 01:09:28prime splice site
- 01:09:30okay they're gonna cleave this portion
- 01:09:31off so what would that look like
- 01:09:32afterwards
- 01:09:34so the snurps come in and they cleave at
- 01:09:36that three prime prime splice site
- 01:09:38and so what's going to be left over here
- 01:09:41is we're going to have
- 01:09:44exon 1 somewhat separated here and
- 01:09:47coming off here what's the three prime
- 01:09:49end contain
- 01:09:50an oh group right and again this is exon
- 01:09:53one then the next thing you have here is
- 01:09:57intron one and it's going to have that
- 01:10:00kind of
- 01:10:01portion here kind of split off if you
- 01:10:02will right kind of broken off here
- 01:10:05and then again over here we're going to
- 01:10:06have still fused at this end
- 01:10:10exon 2.
- 01:10:14so again this is my three prime end
- 01:10:16which has that o h
- 01:10:17this is the five prime end of that
- 01:10:18portion of the axon
- 01:10:20and then again same thing over here this
- 01:10:22is the five prime n of x on two
- 01:10:24three prime n of x on two and then again
- 01:10:27what kind of nucleotides do we have
- 01:10:29in here we have that gu which was pretty
- 01:10:31much the marker which the snurp would
- 01:10:33cut at that three prime site
- 01:10:35then on this five prime splice side i
- 01:10:38still have the ag
- 01:10:40and then here in the middle i have that
- 01:10:41branch point with the adenine with the
- 01:10:43oh group
- 01:10:45here's the next thing that happens the
- 01:10:47oh
- 01:10:48group of that branch point will then
- 01:10:51bind or attack that gu site
- 01:10:56and pull it in to where it kind of fuses
- 01:10:58at this point so it makes kind of like a
- 01:11:00little loop if you will
- 01:11:01so let's show that if it attacks the gu
- 01:11:04and pulls it in
- 01:11:05after that happens you kind of form this
- 01:11:07weird little like loopy structure if you
- 01:11:09will
- 01:11:09so what would that look like if we kind
- 01:11:11of droon after we had that attack
- 01:11:13after that attack point it's going to
- 01:11:15kind of look somewhat
- 01:11:18like this if you will where we have now
- 01:11:22that portion where what would be here
- 01:11:24what would be the kind of the nucleotide
- 01:11:26sequence at that point right there g
- 01:11:30and u was attacked at that point
- 01:11:33by the o h at that branch point
- 01:11:36then the next thing happens this is
- 01:11:40crazy
- 01:11:41this three prime o h of exon one
- 01:11:45will then see that five prime splice
- 01:11:48site
- 01:11:49and it'll attack the five prime splice
- 01:11:53site at exon two
- 01:11:55when it attacks it it then breaks away
- 01:11:59the nucleotide sequence ag of this
- 01:12:01intron away from exon two
- 01:12:04so okay now let's show what that would
- 01:12:06look like
- 01:12:09so if the three prime o h attacks the
- 01:12:12five prime n
- 01:12:13three prime o h of x on one attacks the
- 01:12:15five prime n of x on two
- 01:12:17now what do we have here
- 01:12:20exon one fused
- 01:12:25with exon two and we just
- 01:12:29fused the exons and then what do we spit
- 01:12:32out
- 01:12:32after we break this off
- 01:12:37the intron lariat which i showed you
- 01:12:40like that before
- 01:12:43that is how this whole splicing process
- 01:12:45technically occurs
- 01:12:47super quick again snurps bind
- 01:12:51what do they do cut the three prime
- 01:12:52splice side on between exon one
- 01:12:54intron one when it does that the
- 01:12:57o h of the uh adenine at the branch
- 01:13:00point
- 01:13:00attacks the gu site pulls it in creates
- 01:13:03this loop
- 01:13:04the three prime oh of axon one attacks
- 01:13:07the five prime man of axon two
- 01:13:09which snaps the intron out and stitches
- 01:13:12together
- 01:13:13exon one and exon two that is splicing
- 01:13:16you're like zach why the heck do i need
- 01:13:18to know all this crap
- 01:13:20there's a reason why whenever there's
- 01:13:22abnormalities within splicing it can
- 01:13:24produce a various amounts of diseases
- 01:13:26because think about it
- 01:13:27if i don't cut out the introns properly
- 01:13:31and i have introns mixed in with the
- 01:13:33exons and
- 01:13:34introns don't code for amino acids am i
- 01:13:37going to make a proper protein
- 01:13:39no because i'm going to have areas that
- 01:13:40will code free amino acids in areas that
- 01:13:42don't code for amino acids
- 01:13:44you know there's a very devastating
- 01:13:46condition called spinal
- 01:13:48muscular atrophy where they
- 01:13:51are deficient in an smn protein you want
- 01:13:54to know why
- 01:13:56because the snurps aren't working
- 01:13:58properly
- 01:13:59so there's a deficiency or there's a
- 01:14:01problem
- 01:14:02with the snurps not performing the
- 01:14:05proper splicing
- 01:14:06you know what else there's another
- 01:14:08disease called beta thalassemia
- 01:14:11beta thalassemia guess what you don't
- 01:14:13remove a particular intron
- 01:14:15and because you don't remove that intron
- 01:14:16you make a protein that's abnormal
- 01:14:18and it produces beta thalassemia so
- 01:14:21there's
- 01:14:21reasons to know this stuff and again if
- 01:14:24someone has spinal muscular atrophy
- 01:14:26do you know what that affects the
- 01:14:28anterior gray horn neurons and then they
- 01:14:30develop lower motor neuron lesions
- 01:14:32hypotonia hyperreflexia
- 01:14:34floppy baby syndrome right so it's a
- 01:14:35dangerous condition that can be traced
- 01:14:37back to something at the molecular level
- 01:14:39all right now that we talked about this
- 01:14:41there's two more things and i promise
- 01:14:43we're done all right nature so i want to
- 01:14:44talk about two more things and then
- 01:14:45we're done the first thing i want to
- 01:14:46talk about because it's
- 01:14:47very pretty much similar to what we
- 01:14:49talked about over here with splicing
- 01:14:52i want to talk about something called
- 01:14:54alternative
- 01:14:56rna splicing we understand the
- 01:14:59specific reason for splicing it's making
- 01:15:01sure that we
- 01:15:02only utilize exons to code for proteins
- 01:15:05and there's no introns because if we
- 01:15:06have introns in there
- 01:15:07it's going to frack up the whole protein
- 01:15:09production process we'll get an abnormal
- 01:15:11protein
- 01:15:12with alternative rna splicing
- 01:15:15it gives variance
- 01:15:19of a protein and i'll give you guys an
- 01:15:23example
- 01:15:24in just a second but let me kind of talk
- 01:15:26about how this works it's literally the
- 01:15:27same thing
- 01:15:28we're not going to go too ham on this
- 01:15:31let's use the same colors here
- 01:15:33here was exon one and then here we had
- 01:15:37intron 1 and we'll just skip this part
- 01:15:39here where that was intron 2
- 01:15:41and then blue here we had x on 2
- 01:15:45and then at the end here we had in black
- 01:15:50exon 3 okay
- 01:15:53so let's say that we take an example
- 01:15:55here of of of
- 01:15:57this kind of hn rna right so here's our
- 01:16:00h
- 01:16:02and rna and we want to make different
- 01:16:04mrnas
- 01:16:05that'll give variance of proteins so
- 01:16:08let's say here that we have
- 01:16:09i'm just going to put x on one i'm going
- 01:16:12to do all the same color here exon 2
- 01:16:15exon 3 and then here in between we're
- 01:16:18going to have
- 01:16:20intron 1 and intron 2.
- 01:16:24here's what i can do which is really
- 01:16:26interesting and it's very
- 01:16:28cool when it comes to plasma cells and
- 01:16:30antibodies
- 01:16:32so let's say i use those snurps right so
- 01:16:35let's say here i put
- 01:16:36my snurpees right my snurps which are my
- 01:16:39small
- 01:16:40nuclear rival nuclear proteins with the
- 01:16:41snra and the proteins
- 01:16:43they're going to splice but they're
- 01:16:45going to do it in a very interesting way
- 01:16:47so let's say that the first one over
- 01:16:48here we get the same thing that we did
- 01:16:50with that whole process of splicing
- 01:16:51where we got rid of
- 01:16:53all the introns and we only have in
- 01:16:55exons
- 01:16:56and let's say that we have exon one
- 01:17:01let's say that we have exon two
- 01:17:05and then we have exon three right so we
- 01:17:08have all those exons here exon one x on
- 01:17:10two and exon three
- 01:17:12so we'll put these exon three exon two
- 01:17:16exon one so that's one this is going to
- 01:17:18be mrna right
- 01:17:19after we've kind of done that process
- 01:17:21and it'll give way to a particular
- 01:17:22protein
- 01:17:23and we'll call this protein
- 01:17:27a if you will okay then
- 01:17:31we're going to go through the same thing
- 01:17:32the snurps are going to cleave out the
- 01:17:34entrons and only leave in the exons but
- 01:17:36let's say
- 01:17:37for this example we pop out so this one
- 01:17:40we popped out introns
- 01:17:43but let's say with this one we pop out
- 01:17:45both the introns
- 01:17:46and let's say that we pop out x on two
- 01:17:49let's say that we don't want
- 01:17:50x on two in this one so then what am i
- 01:17:53going to be left with
- 01:17:56i'm going to be left with only exon 1
- 01:18:00and exon 3. and by doing that that's
- 01:18:04going to give me
- 01:18:05an mrna that'll code for another protein
- 01:18:09let's call this protein b and then last
- 01:18:12but not least you guys can already
- 01:18:13probably see where i'm going with this
- 01:18:15let's say that this last one example
- 01:18:17three again we cut out the entrance we
- 01:18:18always got to cut out those introns
- 01:18:20but in this case we cut out
- 01:18:24exon three i don't want that one in the
- 01:18:26diagram i don't want this one in that
- 01:18:27mrna
- 01:18:28so what am i left with i'll be left with
- 01:18:32exon one and i'll be left with
- 01:18:35exon two and what will this code for
- 01:18:39this will code for this will give an
- 01:18:42mrna
- 01:18:44that'll then do what code four another
- 01:18:46protein and let's call this protein
- 01:18:49c from one
- 01:18:52h and rna we made three
- 01:18:55different mrnas and made three proteins
- 01:18:59from the same h and rna or from the same
- 01:19:02kind of
- 01:19:03a gene if you will that means it's going
- 01:19:06to be the same
- 01:19:07protein if it's coming from the same
- 01:19:08gene but it's a variant of that protein
- 01:19:11you know what this is examples of think
- 01:19:13about it guys
- 01:19:15think about plasma cells
- 01:19:18which make antibodies when they make
- 01:19:21antibodies you can have antibodies
- 01:19:24that can be secreted or you can have
- 01:19:27antibodies that are different
- 01:19:28and they're expressed on the cell
- 01:19:29membrane that could be one example
- 01:19:32so antibodies differences in antibodies
- 01:19:35would be an example of how that works
- 01:19:36from
- 01:19:37alternative rna splicing because i'm
- 01:19:38making one protein that'll bind to the
- 01:19:40membrane
- 01:19:40and one protein that can be secreted
- 01:19:42think about neurons
- 01:19:44let's say here's one neuron and this
- 01:19:46neuron
- 01:19:47has a dopamine receptor dopamine 1
- 01:19:50receptor
- 01:19:52but then you have another neuron
- 01:19:56and this has a dopamine 2
- 01:19:59receptor it's the same gene that's
- 01:20:02making these proteins but just a variant
- 01:20:04of it
- 01:20:05and then the last thing is take an
- 01:20:06example of a muscle within the heart
- 01:20:10called tropomyosin and the muscle
- 01:20:13and then within the skeletal muscles
- 01:20:15tropomyosin they're different they're
- 01:20:18small
- 01:20:18changes or variants within the protein
- 01:20:20that are coming from the same
- 01:20:22gene so one of the things that they'll
- 01:20:24love to ask on your exam questions is
- 01:20:25alternative rna splicing
- 01:20:27gives you takes one gene one h and rna
- 01:20:30gives you multiple
- 01:20:31mrnas and variants of the same protein
- 01:20:33if you give examples something like
- 01:20:35immunoglobulins dopamine receptors of
- 01:20:38the brain
- 01:20:39or tropomyosin variant within cardiac
- 01:20:41and skeletal muscle
- 01:20:42all right engineers i promise i'm so
- 01:20:44sorry for this being so long but there's
- 01:20:45one last thing that i want us to talk
- 01:20:47about
- 01:20:48the last thing that i want us to discuss
- 01:20:49is called rna editing
- 01:20:51this is also mentioned a lot
- 01:20:54in your exams and the reason why is
- 01:20:58it's it's really interesting kind of how
- 01:21:00this happens
- 01:21:01there's two different types of rna
- 01:21:03editing i only want to mention really
- 01:21:05one of them
- 01:21:05because it's the most relevant to your
- 01:21:07usmles and in kind of a clinical setting
- 01:21:11so let's say here we have our mrna right
- 01:21:13so this is an
- 01:21:14hn rna we've already at this point in
- 01:21:16time for rna editing we've already
- 01:21:18formed
- 01:21:18our functional mrna so at this point in
- 01:21:21time
- 01:21:22this structure here is a mrna
- 01:21:26okay this mrna
- 01:21:30can have a particular nucleotide
- 01:21:33sequence
- 01:21:34that a special enzyme can read and
- 01:21:37sometimes
- 01:21:38switch nucleotides with what is that
- 01:21:41nucleotide sequence which can be seen in
- 01:21:42this
- 01:21:43mrna which we really want to know it's c
- 01:21:46a a we're going to be talking about
- 01:21:48apoproteins that's why i'm mentioning
- 01:21:50caa
- 01:21:51so this is our signal which is really
- 01:21:54really important within this
- 01:21:56mrna which is going to be making april
- 01:21:58proteins a particular protein called
- 01:22:00let's say that this mrna is going to
- 01:22:01code for a particular protein called apo
- 01:22:06b100 if you guys watch our lipoprotein
- 01:22:09metabolism video
- 01:22:10this will sound familiar right but
- 01:22:13april b100 this is going to be the mr
- 01:22:15enable that will code for that protein
- 01:22:16and here's a particular nucleotide
- 01:22:17sequence that we're going to modify
- 01:22:20in the hepatocytes this nucleotide
- 01:22:22sequence
- 01:22:24is not altered in any way it's kept the
- 01:22:26same
- 01:22:27so it's not going to be changed it's
- 01:22:29still going to be c a a
- 01:22:31and whenever this mrna is translated by
- 01:22:33ribosomes
- 01:22:34it makes a particular protein that we
- 01:22:36already talked about called apob
- 01:22:38100 but in enterocytes
- 01:22:43okay your gi cells what are these cells
- 01:22:46here called these are called your
- 01:22:47enterocytes they have a very special
- 01:22:51enzyme
- 01:22:52where they can modify the same gene that
- 01:22:56makes april b100 but make a different
- 01:22:58protein how the heck
- 01:23:00how do they do that let me explain
- 01:23:03there's this cute little blue
- 01:23:04enzyme in the enterocytes called
- 01:23:07cytidine
- 01:23:11d-aminase
- 01:23:14and what the cytidine deaminase does is
- 01:23:17is it deaminates the cytodine right here
- 01:23:20or the
- 01:23:21cytosine nitrogenous base and
- 01:23:24switches it with uracil
- 01:23:27so now let's switch it here where we're
- 01:23:29going to have this as switching c
- 01:23:32and putting u a a
- 01:23:35if you guys know anything about your
- 01:23:38codons
- 01:23:39there's a little trick to remember your
- 01:23:40stop codons you guys remember the
- 01:23:42the little way to remember them you
- 01:23:44remember by
- 01:23:46you go away you are away
- 01:23:49you are gone these are the easy ways to
- 01:23:52remember your stop codons does any of
- 01:23:54these look like a stop codon
- 01:23:56yes uaa ua that's a stop codon
- 01:24:00so what's going to happen is when you
- 01:24:02have the ribosomes which will be reading
- 01:24:04this let's say here i kind of put like a
- 01:24:05little ribosome
- 01:24:07it's going to be reading this and making
- 01:24:09a particular protein
- 01:24:10as it gets to this point where it's
- 01:24:12going to translate it that's a stop
- 01:24:14codon
- 01:24:15will it then read the rest of the rna
- 01:24:17and translate that into a long protein
- 01:24:19no so at this point translation will
- 01:24:23stop
- 01:24:23you won't read all the rest of the mrna
- 01:24:26and make the full protein
- 01:24:28instead you'll make a smaller protein
- 01:24:32and this small protein is called apo
- 01:24:35b-48
- 01:24:37this is something that they love to ask
- 01:24:40on your exams because
- 01:24:41you're taking the same mrna just
- 01:24:44modifying it a little bit
- 01:24:47to produce a different protein that is a
- 01:24:50completely different sized protein
- 01:24:52so that's really cool definitely wanted
- 01:24:54you guys to know that
- 01:24:55and that finishes our lecture on dna
- 01:24:57transcription all right ninja nurse so
- 01:24:59in this video we talk a ton about dna
- 01:25:01transcription i hope it made sense and i
- 01:25:02hope that you guys did enjoy it
- 01:25:04as always ninja nerds until next time
- 01:25:12[Music]
- 01:25:28you
- DNA-transkription
- RNA-polymeras
- promotorregion
- eukaryoter
- prokaryoter
- transkriptionsfaktorer
- enhancers
- silencers
- RNA-splitsning
- RNA-redigering