Lesson Video - Genetic Mutations

00:25:56
https://www.youtube.com/watch?v=82nI_wVdMyw

Ringkasan

TLDRCette leçon traite des mutations génétiques, en expliquant leur nature, leurs types et leurs effets sur les organismes. Les mutations peuvent être somatiques (affectant les cellules du corps) ou germinales (affectant les cellules reproductrices). Les mutations dans les régions codantes de l'ADN peuvent entraîner des changements dans les protéines, tandis que celles dans les régions non codantes ont généralement moins d'impact. Les types de mutations incluent les substitutions, les insertions et les suppressions, chacune ayant des effets variés sur la séquence protéique. Les mutations peuvent être spontanées, résultant d'erreurs lors de la réplication de l'ADN, ou induites par des agents environnementaux appelés mutagènes. Les conséquences des mutations peuvent être morphologiques, biochimiques ou même létales, selon leur nature et leur emplacement.

Takeaways

  • 🧬 Les mutations sont des changements dans le code ADN.
  • 🔬 Les mutations peuvent être somatiques ou germinales.
  • ⚛️ Les mutations dans les régions codantes affectent les protéines.
  • 💡 Les mutations silencieuses n'affectent pas la séquence d'acides aminés.
  • ⚠️ Les mutations de non-sens créent des codons stop prématurés.
  • 🌱 Les mutations peuvent entraîner des changements morphologiques.
  • 🧪 Les mutations peuvent être induites par des mutagènes.
  • 📉 Les mutations peuvent avoir des effets létaux.
  • 🔄 Les insertions et suppressions entraînent des mutations de décalage de cadre.
  • 📊 Les mutations peuvent être spontanées ou induites par l'environnement.

Garis waktu

  • 00:00:00 - 00:05:00

    Dans cette leçon, Miss Romani introduit le concept de mutations génétiques, en soulignant que leur représentation dans les médias est souvent irréaliste. Elle explique que les mutations sont des changements dans le code ADN et qu'il existe d'autres types d'anomalies génétiques, comme les anomalies chromosomiques. La leçon se concentre uniquement sur les mutations génétiques, en distinguant les mutations somatiques, qui se produisent dans les cellules du corps, des mutations germinales, qui affectent les cellules reproductrices et peuvent avoir des conséquences à long terme sur l'organisme.

  • 00:05:00 - 00:10:00

    Miss Romani aborde les différents types de mutations en fonction de leur localisation dans le corps. Les mutations somatiques, qui se produisent dans les cellules du corps, peuvent entraîner des cancers, tandis que les mutations germinales, qui se produisent dans les cellules reproductrices, affectent l'ensemble de l'organisme et peuvent causer des maladies génétiques. Elle souligne l'importance de protéger les organes reproducteurs lors des examens médicaux pour éviter des mutations potentiellement dangereuses.

  • 00:10:00 - 00:15:00

    La leçon se penche ensuite sur les effets des mutations en fonction de leur emplacement dans la molécule d'ADN. La majorité de l'ADN est non codant, et les mutations dans ces régions n'ont généralement pas d'effet significatif. Miss Romani explique que les mutations dans les régions codantes, qui représentent environ 1 % de l'ADN, peuvent avoir des conséquences variées sur la séquence protéique, en introduisant des mutations de substitution, d'insertion ou de suppression.

  • 00:15:00 - 00:20:00

    Miss Romani décrit les différents types de mutations, notamment les mutations ponctuelles, qui affectent une seule paire de bases, et les mutations non ponctuelles, qui affectent plusieurs paires de bases. Elle explique les effets de ces mutations sur les séquences protéiques, y compris les mutations de sens, silencieuses et sans sens, ainsi que les mutations de décalage de cadre qui peuvent entraîner des changements majeurs dans la protéine produite.

  • 00:20:00 - 00:25:56

    Enfin, Miss Romani conclut en discutant des causes des mutations, qui peuvent être spontanées ou induites par des agents environnementaux appelés mutagènes. Elle souligne que les mutations peuvent avoir des effets variés sur les organismes, allant de changements morphologiques à des maladies génétiques, et que certaines mutations peuvent être létales.

Tampilkan lebih banyak

Peta Pikiran

Video Tanya Jawab

  • Qu'est-ce qu'une mutation génétique ?

    Une mutation génétique est un changement dans le code ADN qui peut affecter la fonction des gènes.

  • Quels sont les types de mutations ?

    Les types de mutations incluent les mutations somatiques et germinales, ainsi que les substitutions, insertions et suppressions.

  • Quelles sont les conséquences des mutations sur les protéines ?

    Les mutations peuvent entraîner des changements dans la séquence des acides aminés, affectant ainsi la structure et la fonction des protéines.

  • Qu'est-ce qu'une mutation silencieuse ?

    Une mutation silencieuse est une substitution qui n'affecte pas l'acide aminé codé par le gène.

  • Comment les mutations peuvent-elles être induites ?

    Les mutations peuvent être induites par des agents environnementaux appelés mutagènes, comme les radiations ou certains produits chimiques.

  • Qu'est-ce qu'une mutation germinale ?

    Une mutation germinale se produit dans les cellules reproductrices et peut affecter l'ensemble de l'organisme.

  • Qu'est-ce qu'une mutation somatique ?

    Une mutation somatique se produit dans les cellules du corps et n'affecte pas les descendants.

  • Quels sont les effets des mutations sur les organismes ?

    Les mutations peuvent entraîner des changements morphologiques, biochimiques ou être létales.

  • Qu'est-ce qu'une mutation de sens ?

    Une mutation de sens est une mutation qui remplace un codon stop par un codon codant pour un acide aminé.

  • Qu'est-ce qu'une mutation de non-sens ?

    Une mutation de non-sens est une mutation qui crée un codon stop prématuré, entraînant une protéine plus courte.

Lihat lebih banyak ringkasan video

Dapatkan akses instan ke ringkasan video YouTube gratis yang didukung oleh AI!
Teks
en
Gulir Otomatis:
  • 00:00:00
    hi everyone this is miss romani and for
  • 00:00:02
    today's lesson we're going to learn
  • 00:00:03
    about genetic mutations
  • 00:00:05
    the concept of genetic mutations is
  • 00:00:07
    actually one that has been popularized
  • 00:00:09
    quite a bit in comic books and in
  • 00:00:10
    mainstream media
  • 00:00:12
    however the way the mutations are
  • 00:00:14
    represented is not usually realistic
  • 00:00:17
    the idea that changes in our dna can
  • 00:00:20
    give us superpowers is appealing
  • 00:00:22
    but and i'm sorry if that disappoints
  • 00:00:24
    some of you
  • 00:00:25
    it is entirely unrealistic and so
  • 00:00:29
    mutations are basically changes to the
  • 00:00:32
    dna code
  • 00:00:33
    they are not the only type of genetic
  • 00:00:36
    abnormalities or
  • 00:00:37
    not the only cause of genetic
  • 00:00:38
    abnormalities changes in the number
  • 00:00:41
    or in the structure of our chromosomes
  • 00:00:44
    something that we call chromosomal
  • 00:00:45
    abnormalities the topic of what happens
  • 00:00:47
    when you have extra chromosomes to a few
  • 00:00:49
    chromosomes or
  • 00:00:50
    pieces missing of chromosomes and so on
  • 00:00:52
    that was covered in the grade 11 course
  • 00:00:55
    today's lesson will focus only on
  • 00:00:57
    genetic mutations
  • 00:00:58
    so let's begin by taking a look at the
  • 00:01:00
    locations of mutations and where they
  • 00:01:02
    can happen
  • 00:01:04
    so first let's take a look at where they
  • 00:01:06
    can happen within the body
  • 00:01:07
    and there are two main places where
  • 00:01:10
    mutations can happen within the body
  • 00:01:12
    the first type are in the somatic cells
  • 00:01:16
    and so we call
  • 00:01:17
    those somatic mutations somatic
  • 00:01:19
    mutations are mutations that happen
  • 00:01:21
    in our body cells so you might think
  • 00:01:24
    well isn't
  • 00:01:25
    all our cells our body cells well as far
  • 00:01:28
    as biology is concerned
  • 00:01:29
    we differentiate body cells which are
  • 00:01:32
    somatic cells which are basically
  • 00:01:33
    most of the cells in your body from the
  • 00:01:36
    cells that are found within your sex
  • 00:01:38
    organs the cells that are found in your
  • 00:01:41
    egg producing ovaries or your sperm
  • 00:01:44
    producing testes
  • 00:01:45
    so somatic mutations are basically the
  • 00:01:48
    ones that happen in any of your cells in
  • 00:01:50
    your body that are just going to
  • 00:01:52
    undergo mitosis and are not the result
  • 00:01:54
    of meiosis
  • 00:01:56
    if you have a somatic mutation it'll
  • 00:01:58
    have
  • 00:01:59
    an effect on a part of your body that is
  • 00:02:01
    affected by
  • 00:02:02
    the mutation the cells that have the
  • 00:02:04
    genetic mutation
  • 00:02:05
    are going to be the progeny of those
  • 00:02:10
    cells with a mutation
  • 00:02:11
    somatic mutations can happen in the womb
  • 00:02:14
    but
  • 00:02:14
    most often they happen once you are
  • 00:02:16
    already born and throughout your lives
  • 00:02:18
    and this is something that we contend
  • 00:02:20
    with
  • 00:02:20
    constantly and oftentimes these types of
  • 00:02:23
    mutations just lead to
  • 00:02:25
    cancers really if anything at all
  • 00:02:29
    the other type of mutation which is the
  • 00:02:31
    one that is most concerning
  • 00:02:33
    in terms of lifelong effects and more
  • 00:02:36
    severe effects are what we call
  • 00:02:37
    germline mutations and these are the
  • 00:02:39
    mutations that occur in our sex organs
  • 00:02:42
    are egg producing ovaries or sperm
  • 00:02:44
    producing testes
  • 00:02:46
    or if they occur on the embryo really
  • 00:02:49
    early on
  • 00:02:50
    in development so maybe in the zygote or
  • 00:02:53
    you know one of the earlier stages of
  • 00:02:55
    embryonic development
  • 00:02:57
    and with germline mutation the entire
  • 00:02:59
    organism
  • 00:03:00
    is affected by the genetic mutation
  • 00:03:03
    because
  • 00:03:04
    if the mutation was on the sperm or the
  • 00:03:06
    egg
  • 00:03:07
    then every single piece of dna that
  • 00:03:10
    the organism has will have that genetic
  • 00:03:13
    mutation
  • 00:03:14
    and so germline mutations are more
  • 00:03:16
    dangerous because they don't just affect
  • 00:03:18
    a little tiny part of your body will
  • 00:03:20
    affect your entire body
  • 00:03:21
    and oftentimes these are the types of
  • 00:03:23
    mutations that lead to genetic diseases
  • 00:03:25
    or genetic disorders germline mutations
  • 00:03:29
    are also the reason why whenever you go
  • 00:03:30
    get an x-ray taken
  • 00:03:32
    they will make sure that they'll cover
  • 00:03:34
    your genital area with a lead
  • 00:03:37
    bib or a lead blanket because any
  • 00:03:40
    mutations that can occur
  • 00:03:41
    in your eggs or sperm cells or your egg
  • 00:03:44
    and sperm producing organs
  • 00:03:46
    could have possibly lifelong and serious
  • 00:03:50
    effect
  • 00:03:50
    on your offspring from the in the future
  • 00:03:54
    so we've categorized the different
  • 00:03:56
    effects that genetic mutations can have
  • 00:03:57
    depending on which types of cells they
  • 00:03:59
    occur
  • 00:04:00
    in but how about we take a look at
  • 00:04:03
    what are the different effects of
  • 00:04:04
    genetic mutations depending on where
  • 00:04:06
    they occur within the dna molecule
  • 00:04:08
    itself
  • 00:04:09
    and so that is the difference between
  • 00:04:11
    mutations that occur
  • 00:04:12
    in sections of our dna that we call
  • 00:04:14
    coding regions versus sections of our
  • 00:04:16
    dna which we call non-coding region
  • 00:04:19
    and it might surprise a lot of you to
  • 00:04:20
    learn that as a matter of fact
  • 00:04:22
    most of our dna is what we consider to
  • 00:04:25
    be non-coding dna
  • 00:04:27
    some estimates estimate that about 99 of
  • 00:04:30
    our dna
  • 00:04:30
    is actually non-coding with only one
  • 00:04:33
    percent or so of our dna
  • 00:04:35
    coding for genes and coding for proteins
  • 00:04:39
    when scientists first figure that out
  • 00:04:41
    when they finished the
  • 00:04:42
    human genome project they were extremely
  • 00:04:44
    surprised to find that so much of our
  • 00:04:46
    dna
  • 00:04:46
    was actually what they at the time
  • 00:04:48
    called junk dna
  • 00:04:50
    because they didn't know what it did
  • 00:04:51
    they just knew that it did not actually
  • 00:04:53
    code for
  • 00:04:54
    proteins and so therefore vast amounts
  • 00:04:56
    of our dna was not
  • 00:04:58
    containing the instructions for our
  • 00:05:00
    bodies so
  • 00:05:01
    imagine if we go back to the recipe book
  • 00:05:03
    analogy that i gave you before
  • 00:05:06
    and one percent of the recipe book was
  • 00:05:09
    actually recipes and 99 of it was
  • 00:05:12
    what at first appeared to be just
  • 00:05:14
    nonsense that did not contain any
  • 00:05:17
    recipes
  • 00:05:18
    and so when dna mutations happen in what
  • 00:05:21
    we call
  • 00:05:22
    non-coding regions of the cell the
  • 00:05:24
    effects of those genetic mutations are
  • 00:05:26
    going to be
  • 00:05:26
    vastly different than when they occur in
  • 00:05:29
    the genes themselves so they can happen
  • 00:05:31
    in
  • 00:05:31
    the vast areas of the dna
  • 00:05:34
    molecule that are in between the genes
  • 00:05:37
    but even within the genes if you
  • 00:05:38
    remember from our last lesson we have
  • 00:05:40
    both axons and introns
  • 00:05:42
    so sometimes you can have mutations that
  • 00:05:44
    happen within introns within the gene
  • 00:05:46
    itself
  • 00:05:46
    and so those types of mutations are not
  • 00:05:49
    going to be
  • 00:05:50
    as detrimental to the organisms as
  • 00:05:52
    mutations that happen within
  • 00:05:54
    the actual genetic code that codes for
  • 00:05:56
    proteins
  • 00:05:57
    within the exons of genes that are then
  • 00:06:01
    going to
  • 00:06:01
    be interpreted and read and transcribed
  • 00:06:04
    and translated into an
  • 00:06:06
    actual protein and when we take a look
  • 00:06:08
    at the junk dna though just to clarify
  • 00:06:11
    again
  • 00:06:11
    so i don't want you to kind of come out
  • 00:06:13
    of this lesson with an idea that most of
  • 00:06:15
    our dna has
  • 00:06:16
    no purpose whatsoever there's many
  • 00:06:18
    different purposes that we've so far
  • 00:06:20
    found for a lot of our dna and this is
  • 00:06:23
    an area of biology
  • 00:06:24
    and genetics that is yet to be fully
  • 00:06:27
    explored there's a lot that we still
  • 00:06:29
    want to learn about that
  • 00:06:30
    but one of the things that we've learned
  • 00:06:33
    is that first of all some of that
  • 00:06:35
    non-coding dna can be the introns within
  • 00:06:38
    the coding sequence so those
  • 00:06:40
    genes that have those introns within
  • 00:06:42
    them that are not necessarily going to
  • 00:06:44
    then be part of the
  • 00:06:45
    mrna transcript that exits the nucleus
  • 00:06:48
    for translation but then there's other
  • 00:06:50
    sections for example
  • 00:06:52
    one thing that we find is that a lot of
  • 00:06:53
    our dna is composed of these things
  • 00:06:55
    called repetitive elements
  • 00:06:56
    and repetitive elements could be say for
  • 00:06:59
    example the genetic code
  • 00:07:01
    gac gac repeated maybe hundreds and
  • 00:07:04
    hundreds or thousands of times
  • 00:07:06
    and we don't know why that is but you
  • 00:07:09
    know this is an
  • 00:07:10
    area of dna that is very vast within our
  • 00:07:13
    genome
  • 00:07:13
    that just happens to be there for so far
  • 00:07:17
    unknown reasons
  • 00:07:18
    we also know that some of our dna that
  • 00:07:20
    is non-coding
  • 00:07:21
    is actually the remnants of viral
  • 00:07:24
    infections from the past
  • 00:07:25
    so these are types of viruses called
  • 00:07:27
    retroviruses these are viruses that can
  • 00:07:30
    when they infect our cells they insert
  • 00:07:33
    their dna code within our genome itself
  • 00:07:36
    and any time that that has happened
  • 00:07:39
    within the history of humanity and not
  • 00:07:41
    just humans but
  • 00:07:43
    our ancestors within the history of our
  • 00:07:45
    evolution
  • 00:07:47
    if those retroviruses inserted their dna
  • 00:07:50
    within germline cells then their dna
  • 00:07:53
    ends up being part of our genome today
  • 00:07:55
    so a lot of our dna
  • 00:07:58
    is also dna that came from viruses that
  • 00:08:00
    infected
  • 00:08:02
    our ancestors and going
  • 00:08:05
    all the way back to the earliest cell
  • 00:08:08
    we can actually do dna analysis in order
  • 00:08:10
    to determine the level of relatedness
  • 00:08:12
    between species so one of the things
  • 00:08:14
    that we look for sometimes
  • 00:08:15
    is those viral pieces of dna because
  • 00:08:19
    if you find similarities in those
  • 00:08:20
    retrovirus
  • 00:08:22
    then you can determine whether or not
  • 00:08:24
    they are related to each other to a
  • 00:08:25
    certain degree
  • 00:08:26
    some of our dna that is considered to be
  • 00:08:28
    junk dna actually has a very important
  • 00:08:30
    function as regulatory sequences so
  • 00:08:33
    these are actual
  • 00:08:35
    pieces of dna that may not code for
  • 00:08:37
    proteins but they might code for say
  • 00:08:40
    trna that are involved in translation
  • 00:08:43
    or micro rna that are involved in
  • 00:08:47
    regulating gene expression
  • 00:08:49
    or even some of the proteins that
  • 00:08:52
    are involved as transcription factors or
  • 00:08:55
    something like that
  • 00:08:56
    so these are sequences of dna that may
  • 00:08:58
    not code for genes
  • 00:08:59
    that produce proteins that we use in our
  • 00:09:01
    body but they might code for
  • 00:09:03
    other proteins or rna that is used
  • 00:09:07
    during the regulation of our genetic
  • 00:09:10
    expression
  • 00:09:11
    and then last we have a lot of what are
  • 00:09:14
    called pseudogenes
  • 00:09:16
    these are genes that are not turned on
  • 00:09:18
    anymore
  • 00:09:19
    these are probably the remnants of our
  • 00:09:21
    evolutionary history
  • 00:09:23
    you know genes for traits that we no
  • 00:09:25
    longer carry
  • 00:09:26
    that we no longer express but their
  • 00:09:29
    history is there within our code
  • 00:09:30
    so there's a lot of reasons why we have
  • 00:09:32
    all this junk dna
  • 00:09:34
    and last also we have areas of our
  • 00:09:37
    chromosomes that are filled with
  • 00:09:38
    repeated sequences that are non-coding
  • 00:09:41
    that have actually
  • 00:09:42
    a purpose structurally within the
  • 00:09:44
    chromosome so for example
  • 00:09:46
    the centromere where the two chromatids
  • 00:09:49
    attach
  • 00:09:49
    in the center that's a lot of non-coding
  • 00:09:53
    regions of dna
  • 00:09:54
    and then at the ends of our dna we have
  • 00:09:57
    vast sections that are called telomeres
  • 00:10:00
    telomeres
  • 00:10:01
    are vast sections of non-coding
  • 00:10:03
    sequences
  • 00:10:04
    that are serve a purpose to prevent
  • 00:10:08
    the destruction of our genetic code as
  • 00:10:11
    we
  • 00:10:12
    age and as we reproduce so when
  • 00:10:13
    mutations happen
  • 00:10:15
    on 99 of our dna which is the non-coding
  • 00:10:18
    regions
  • 00:10:19
    they are going to have very little to
  • 00:10:22
    zero effect
  • 00:10:23
    on our cells and our bodies because
  • 00:10:25
    they're not the parts of the dna that
  • 00:10:27
    actually contain our genetic code
  • 00:10:28
    that codes for our proteins so let's
  • 00:10:32
    focus then on what happens when
  • 00:10:34
    mutations happen on that one percent of
  • 00:10:36
    our dna that is coding
  • 00:10:37
    we can actually categorize the mutations
  • 00:10:40
    into
  • 00:10:41
    a couple of different types the first
  • 00:10:44
    type is what we call
  • 00:10:45
    point mutations and point mutations are
  • 00:10:47
    basically mutations that occur
  • 00:10:48
    on a single base pair because the dna
  • 00:10:51
    molecule is double stranded whenever we
  • 00:10:53
    take a look at mutations
  • 00:10:54
    we have to take a look at what happens
  • 00:10:56
    to not just a single letter
  • 00:10:57
    but also its complementary base so it's
  • 00:11:00
    always going to be done in pairs
  • 00:11:02
    and there are different types of point
  • 00:11:04
    mutations
  • 00:11:06
    first one is something called the base
  • 00:11:08
    substitution
  • 00:11:09
    substitutions as the name implies are
  • 00:11:11
    basically when
  • 00:11:12
    one letter is replaced or substituted
  • 00:11:15
    with another
  • 00:11:16
    and so there's two types of base
  • 00:11:18
    substitutions
  • 00:11:19
    the first one are called transversions
  • 00:11:22
    transversions happens when
  • 00:11:23
    appearing is replaced with a pyramidine
  • 00:11:26
    or a pyramidine is replaced with a
  • 00:11:28
    purine so for example in this particular
  • 00:11:30
    example
  • 00:11:31
    you have an initial sequence with a
  • 00:11:34
    thymine
  • 00:11:34
    and the thymine has been replaced with
  • 00:11:36
    an adenine that
  • 00:11:38
    pyrimidine which is thymine is now an
  • 00:11:40
    adenine which is appearing
  • 00:11:42
    and another type of mutation though is
  • 00:11:44
    what we call a transition
  • 00:11:46
    a transition is when a purine is
  • 00:11:48
    replaced with another purine or a
  • 00:11:50
    pyrimidine is replaced with another
  • 00:11:52
    pyrimidine
  • 00:11:53
    so for example you have a guanine that
  • 00:11:55
    is being replaced by an adenine
  • 00:11:57
    guanine and adenine are both purines so
  • 00:12:00
    you're replacing a purine
  • 00:12:01
    with another purine another type of
  • 00:12:04
    point mutation
  • 00:12:05
    are what we called insertions insertions
  • 00:12:08
    as the name implies
  • 00:12:09
    is when we are inserting something
  • 00:12:10
    within the code so this is not
  • 00:12:12
    substituting or replacing
  • 00:12:14
    a base with another base this is
  • 00:12:16
    actually introducing
  • 00:12:17
    another letter within the code itself so
  • 00:12:20
    where the air is pointing right there
  • 00:12:22
    what would happen then if we were to add
  • 00:12:24
    a nucleotide pair right there in the
  • 00:12:27
    middle of that code and so that's an
  • 00:12:29
    insertion it basically makes the dna
  • 00:12:31
    strength a little longer by one base
  • 00:12:33
    pair
  • 00:12:33
    and it can have severe effects on the
  • 00:12:36
    genetic code itself
  • 00:12:37
    the opposite of an insertion is what we
  • 00:12:38
    call the deletion and so let's say
  • 00:12:40
    we remove a pair so for example let's
  • 00:12:43
    remove that
  • 00:12:45
    cytosine to guanine base pair and so now
  • 00:12:47
    the dna strand is a little bit shorter
  • 00:12:49
    by one base pair
  • 00:12:50
    and that is again going to have some
  • 00:12:51
    effects on the genetic code
  • 00:12:54
    and the proteins that it codes for
  • 00:12:56
    non-point mutations
  • 00:12:57
    can also occur these are mutations where
  • 00:13:00
    you have more than one base pair
  • 00:13:02
    affected so you can have
  • 00:13:03
    for example the substitution of more
  • 00:13:05
    than one base pair or
  • 00:13:06
    the in insertion or deletion of
  • 00:13:10
    two or three or more base pairs and so
  • 00:13:13
    the consequences of any of these
  • 00:13:15
    mutations
  • 00:13:16
    the base pair substitutions insertions
  • 00:13:19
    or deletions
  • 00:13:20
    can vary depending on the type of
  • 00:13:23
    mutation that occurs
  • 00:13:25
    and what effect they can have on the
  • 00:13:26
    actual genetic code so
  • 00:13:28
    let's take a look at that next what are
  • 00:13:30
    the effects of those mutations
  • 00:13:32
    on the protein sequence itself
  • 00:13:36
    so for the next few slides we're going
  • 00:13:38
    to take a look at
  • 00:13:39
    several different effects that changes
  • 00:13:41
    in the genetic code can have on the
  • 00:13:43
    protein sequence
  • 00:13:44
    and each of the next few slides are
  • 00:13:46
    going to look very similar to this one
  • 00:13:48
    on the left hand side you have in purple
  • 00:13:51
    the initial non-mutated sequence of a
  • 00:13:54
    strand of dna
  • 00:13:56
    notice that it's double-stranded right
  • 00:13:57
    because dna is double-stranded but then
  • 00:14:00
    you see
  • 00:14:00
    beneath it the mrna the single-stranded
  • 00:14:03
    mrna
  • 00:14:04
    that that dna sequence codes for
  • 00:14:08
    so transcription has happened and we
  • 00:14:10
    have that section of mrna
  • 00:14:12
    and we're going to then show what that
  • 00:14:14
    altered sequence would look like on the
  • 00:14:16
    mrna
  • 00:14:17
    which in turn is then going to be
  • 00:14:19
    translated into a polypeptide
  • 00:14:21
    an amino acid sequence there in blue
  • 00:14:24
    i've also added the genetic code so that
  • 00:14:27
    we can kind of follow along
  • 00:14:29
    to see what the effects of the genetic
  • 00:14:30
    mutations are so let's start with this
  • 00:14:32
    first genetic mutation so you can see
  • 00:14:34
    here
  • 00:14:35
    the mutation has replaced a thymine
  • 00:14:38
    adenine-based pair with a cytosine
  • 00:14:40
    guanine base pair so this is a base
  • 00:14:42
    substitution
  • 00:14:44
    and in the initial sequence the original
  • 00:14:46
    non-mutated sequence
  • 00:14:48
    that particular genetic code would have
  • 00:14:51
    been
  • 00:14:51
    transcribed into an mrna that had a
  • 00:14:54
    codon
  • 00:14:55
    uca remember that the genetic code is
  • 00:14:58
    read in three letters
  • 00:14:59
    and each of the three letters is called
  • 00:15:01
    a codon and so when those
  • 00:15:03
    three letters are then translated
  • 00:15:06
    into an amino acid sequence take a look
  • 00:15:09
    at
  • 00:15:10
    the genetic code table at the bottom
  • 00:15:13
    then
  • 00:15:13
    uca would actually code for the amino
  • 00:15:16
    acid serine
  • 00:15:18
    so serine ser that's its short form
  • 00:15:21
    it's found right here now in the mutated
  • 00:15:24
    version of the codon though
  • 00:15:27
    we no longer have uca we now have cca
  • 00:15:30
    and cca no longer codes for serine it
  • 00:15:33
    actually
  • 00:15:33
    codes for proline so now we have one
  • 00:15:37
    altered amino acid
  • 00:15:39
    so in this type of mutation which we
  • 00:15:41
    call the missense mutation
  • 00:15:43
    a single amino acid has been changed due
  • 00:15:46
    to usually
  • 00:15:47
    a single base pair substitution we
  • 00:15:49
    substitute one letter
  • 00:15:51
    in the initial sequence of the genetic
  • 00:15:53
    code which in turn
  • 00:15:54
    leads to a different codon that is going
  • 00:15:57
    to code for a different amino acid so we
  • 00:15:59
    call these
  • 00:16:00
    missense mutations another thing that
  • 00:16:03
    can happen when you have a base pair
  • 00:16:04
    substitution
  • 00:16:05
    so again here we go we're going to
  • 00:16:07
    substitute a different base pair in this
  • 00:16:09
    particular case the thymine to adenine
  • 00:16:11
    is going to
  • 00:16:12
    be substituted into a cytosine to
  • 00:16:14
    guanine but it's a different one
  • 00:16:16
    and in this particular case then the
  • 00:16:19
    codon that is affected
  • 00:16:20
    is the previous codon which is ggu
  • 00:16:24
    now ggu codes for the amino acid glycine
  • 00:16:29
    that's the original code now let's take
  • 00:16:31
    a look at what happens after the
  • 00:16:32
    mutation
  • 00:16:33
    so in this particular case as to the
  • 00:16:34
    mutation the codon
  • 00:16:37
    ggu is now ggc
  • 00:16:40
    let's take a look at what effect that
  • 00:16:42
    has on the
  • 00:16:44
    amino acid that is coded for well ggc
  • 00:16:48
    well it also codes for glycine so
  • 00:16:51
    this particular type of mutation
  • 00:16:54
    actually
  • 00:16:54
    has no effect on the amino acid sequence
  • 00:16:58
    and we call that a silent mutation
  • 00:17:01
    same type of mutation that occurred in
  • 00:17:03
    the previous example with a base pair
  • 00:17:05
    substitution
  • 00:17:06
    but because in the previous example it
  • 00:17:09
    was the first letter
  • 00:17:10
    in the codon that was substituted that
  • 00:17:13
    actually led to
  • 00:17:15
    a different amino acid being coded for
  • 00:17:17
    but because in this particular case it
  • 00:17:19
    is the third letter in the codon that is
  • 00:17:21
    substituted and oftentimes
  • 00:17:23
    the third letter in the codon does not
  • 00:17:26
    really matter
  • 00:17:27
    in terms of determining what amino acid
  • 00:17:29
    is being coded for because many amino
  • 00:17:31
    acids
  • 00:17:32
    are coded for by more than one codon and
  • 00:17:35
    it's usually that third letter
  • 00:17:37
    that might differ between them so in
  • 00:17:39
    this particular case glycine
  • 00:17:41
    is coded for by the codon
  • 00:17:45
    gga ggc ggu
  • 00:17:49
    and ggg so any four of those codons
  • 00:17:53
    would still code for glycine
  • 00:17:54
    so let's take a look at another mutation
  • 00:17:56
    in this particular case
  • 00:17:58
    we have now another base substitution
  • 00:18:00
    we've substituted
  • 00:18:01
    this cytosine to guanine-based pair for
  • 00:18:04
    this adenine to thymine
  • 00:18:05
    in the original codon we have a codon e
  • 00:18:09
    ugc which codes for the amino acid
  • 00:18:12
    cysteine
  • 00:18:13
    right here let's take a look at what
  • 00:18:15
    happens after this mutation
  • 00:18:17
    the new codon is uga
  • 00:18:20
    that's very similar to ugc but in this
  • 00:18:24
    case
  • 00:18:24
    changing that third letter in the codon
  • 00:18:27
    actually
  • 00:18:28
    does not lead to the exact same amino
  • 00:18:30
    acid as the previous
  • 00:18:31
    code but it actually leads to a stop
  • 00:18:34
    codon
  • 00:18:35
    and so with a premature stop codon
  • 00:18:38
    now the sequence is going to be
  • 00:18:40
    terminated when the mrna is read by
  • 00:18:43
    ribosomes it's going to read a stop
  • 00:18:45
    codon
  • 00:18:46
    very early on in the mrna sequence and
  • 00:18:49
    is going to terminate translation
  • 00:18:51
    and a polypeptide that might have been
  • 00:18:53
    maybe a thousand amino acids
  • 00:18:56
    long might now just be 10 15
  • 00:18:59
    800 but it's going to be shorter and so
  • 00:19:02
    whenever that happens we call that a
  • 00:19:03
    nonsense mutation
  • 00:19:05
    a nonsense mutation is a mutation that
  • 00:19:07
    causes one of those three stop codons to
  • 00:19:09
    appear
  • 00:19:11
    somewhere within the genetic code well
  • 00:19:14
    before it is meant to appear
  • 00:19:16
    which shortens the length of the
  • 00:19:17
    polypeptide
  • 00:19:19
    the opposite of that would be what we
  • 00:19:20
    call the sense mutation
  • 00:19:22
    a sense mutation would be one in which a
  • 00:19:24
    stop codon is lost
  • 00:19:26
    so this would be a mutation in which say
  • 00:19:29
    the original
  • 00:19:30
    code might have been uga which coded for
  • 00:19:33
    a stop codon
  • 00:19:34
    but now let's say for example that
  • 00:19:36
    changes to ugc
  • 00:19:38
    say and then so now instead of having a
  • 00:19:40
    stop codon we add a cysteine amino acid
  • 00:19:43
    and then the mrna is going to continue
  • 00:19:45
    to be red and adding more amino acids so
  • 00:19:48
    you end up with a protein that is longer
  • 00:19:50
    than the original protein
  • 00:19:51
    and so having a shorter protein or a
  • 00:19:53
    longer protein
  • 00:19:54
    sequence is going to be detrimental to
  • 00:19:57
    the shape of the protein and therefore
  • 00:19:59
    the function of the proteins
  • 00:20:00
    so let's take a look at what happens
  • 00:20:02
    when instead of a base substitution we
  • 00:20:04
    have something called an
  • 00:20:05
    insertion and so in this case let's add
  • 00:20:09
    a base
  • 00:20:10
    right here between that guanine to
  • 00:20:12
    cytoscene
  • 00:20:13
    and guanine to cytosine bases let's add
  • 00:20:16
    one base pair right there and so the
  • 00:20:19
    original
  • 00:20:20
    code would code for the codon ggu
  • 00:20:23
    in the original sequence which codes for
  • 00:20:26
    the amino acid glycine
  • 00:20:29
    and after the insertion we now
  • 00:20:32
    have an adenine in between those two
  • 00:20:34
    guanines so instead of being ggu the
  • 00:20:37
    codon will be read as
  • 00:20:39
    gag because now there's an extra letter
  • 00:20:41
    in between those two guanines
  • 00:20:43
    and because ribosomes read the dna code
  • 00:20:47
    three letters at a time regardless of
  • 00:20:49
    what it was meant to be initially
  • 00:20:51
    it's not going to count the fact that
  • 00:20:53
    atomy shouldn't have been there it just
  • 00:20:54
    reads
  • 00:20:54
    the next three letters so the next three
  • 00:20:56
    letters in that mrna sequence
  • 00:20:58
    instead of being ggu is now gag
  • 00:21:02
    and so gag codes for glutamic acid which
  • 00:21:06
    is a completely different amino acid
  • 00:21:09
    but then let's take a look at what
  • 00:21:10
    happens to the code after that point too
  • 00:21:13
    because the next codon in the original
  • 00:21:15
    sequence would have been
  • 00:21:16
    uca which would code for the amino acid
  • 00:21:19
    serine
  • 00:21:20
    and in this new code because we added an
  • 00:21:23
    adenine
  • 00:21:24
    in the previous codon then the uracil
  • 00:21:29
    in that codon instead of being the third
  • 00:21:31
    letter in that codon it becomes the
  • 00:21:33
    first letter on the next codon
  • 00:21:35
    and so instead of having uca
  • 00:21:38
    we now have uuc for the next codon
  • 00:21:42
    and that codes for the amino acid
  • 00:21:44
    phenylalanine
  • 00:21:46
    and then every single codon after that
  • 00:21:50
    is similarly affected
  • 00:21:51
    so essentially by adding a base pair in
  • 00:21:54
    the middle of a genetic sequence
  • 00:21:56
    we've essentially shifted the reading
  • 00:22:00
    frame
  • 00:22:01
    of the mrna so that the codons are read
  • 00:22:04
    off by
  • 00:22:05
    one and so we call this frameshift
  • 00:22:07
    mutations
  • 00:22:08
    and frameshift mutations they
  • 00:22:10
    essentially cause
  • 00:22:12
    every single amino acid from the point
  • 00:22:15
    of the mutation on
  • 00:22:16
    to be different than the original code
  • 00:22:19
    because of a shifting on the reading
  • 00:22:22
    frame of the mrna sequence because
  • 00:22:24
    ribosomes read mrna
  • 00:22:26
    three letters at a time regardless of
  • 00:22:29
    what the initial sequence was supposed
  • 00:22:30
    to be
  • 00:22:31
    frame shift mutations do not only happen
  • 00:22:33
    when you have insertions
  • 00:22:35
    that will also happens when you have
  • 00:22:36
    deletions same effect
  • 00:22:38
    adding a base or removing a base will
  • 00:22:40
    essentially
  • 00:22:41
    shift the reading frame of the
  • 00:22:44
    mrna so that codons are going to be off
  • 00:22:47
    by
  • 00:22:48
    one or if it's two by two from that
  • 00:22:51
    point on
  • 00:22:52
    the only time the friendship mutations
  • 00:22:54
    are not as bad
  • 00:22:55
    is when you have three bases that are
  • 00:22:57
    inserted or deleted
  • 00:22:58
    because the codons are three bases long
  • 00:23:01
    by
  • 00:23:02
    inserting three bases or deleting three
  • 00:23:04
    bases we're essentially just either
  • 00:23:06
    deleting one amino acid or inserting
  • 00:23:08
    an extra amino acid which could have a
  • 00:23:09
    very bad effect but may not
  • 00:23:11
    be that dangerous to the organism as a
  • 00:23:14
    frameshift mutation is which
  • 00:23:16
    essentially creates a completely
  • 00:23:18
    different protein from the point of
  • 00:23:19
    mutation on as with the original
  • 00:23:21
    intended so
  • 00:23:22
    there is no way that this new protein is
  • 00:23:24
    going to work
  • 00:23:25
    at all like it was intended because it
  • 00:23:28
    is essentially a completely different
  • 00:23:30
    code from that from the point of the
  • 00:23:31
    mutation on
  • 00:23:32
    so just very briefly let's just
  • 00:23:34
    summarize the different types of
  • 00:23:36
    mutations and their effects
  • 00:23:37
    substitutions can lead to missense
  • 00:23:39
    mutations silent mutations
  • 00:23:41
    nonsense or sense mutations but they
  • 00:23:43
    never lead to frame shift mutations
  • 00:23:45
    whereas insertions in the lesions will
  • 00:23:47
    always lead to friendship mutations of
  • 00:23:50
    some form
  • 00:23:51
    unless it is three bases that are
  • 00:23:53
    inserted or three
  • 00:23:54
    bases that are deleted but
  • 00:23:57
    this friendship mutations themselves can
  • 00:23:59
    also lead to nonsense mutations
  • 00:24:01
    if i'd stop coding appears too early as
  • 00:24:03
    a result of the frame shift
  • 00:24:05
    or a sense mutation if a stop codon does
  • 00:24:07
    not appear early enough as a result of
  • 00:24:09
    the frame shift
  • 00:24:11
    so let's take a look now how mutations
  • 00:24:13
    can affect the entire organism
  • 00:24:15
    there's a variety of different ways by
  • 00:24:17
    which mutations can affect an organism
  • 00:24:19
    but in general we're going to either see
  • 00:24:21
    maybe something like a morphological
  • 00:24:22
    change which is an
  • 00:24:23
    obvious physical change in
  • 00:24:25
    characteristics of the organism
  • 00:24:27
    biochemical changes are not as obvious
  • 00:24:30
    they're inside the body
  • 00:24:32
    but for example in the case of cystic
  • 00:24:34
    fibrosis a single base pair substitution
  • 00:24:37
    leads to a missense mutation
  • 00:24:39
    with a single amino acid change in the
  • 00:24:42
    cftr
  • 00:24:43
    chloride channel which now produces a
  • 00:24:45
    mutant and non-working chloride channel
  • 00:24:47
    protein which is the cause
  • 00:24:49
    of cystic fibrosis and of course
  • 00:24:52
    mutations can sometimes be lethal
  • 00:24:54
    if they're completely incompatible with
  • 00:24:55
    life the causes of mutations are
  • 00:24:58
    basically two-fold
  • 00:24:59
    they can either occur spontaneously
  • 00:25:02
    during
  • 00:25:03
    errors that occur naturally during dna
  • 00:25:05
    replication
  • 00:25:06
    that either missed by the last step
  • 00:25:09
    which is the proofreading step of dna
  • 00:25:11
    replication
  • 00:25:12
    and therefore accumulate in the cell and
  • 00:25:15
    this is one of the main causes of both
  • 00:25:17
    aging and cancers just
  • 00:25:19
    natural spontaneous errors and dna
  • 00:25:21
    replication
  • 00:25:22
    but they can also be induced by our
  • 00:25:24
    environment so these are what we call
  • 00:25:25
    induced mutations and induced mutations
  • 00:25:27
    can come from
  • 00:25:28
    a variety of different forms or
  • 00:25:30
    environmental agents called mutagens and
  • 00:25:32
    mutagens can be things like radiation
  • 00:25:34
    like uv radiation or x-rays chemicals in
  • 00:25:38
    our environment
  • 00:25:39
    chemicals in our food or even infectious
  • 00:25:42
    agents like viruses
  • 00:25:44
    or bacteria that can actually cause
  • 00:25:46
    genetic mutations as well
  • 00:25:48
    so there's a variety of different things
  • 00:25:49
    that can cause mutations
  • 00:25:51
    and so that's the lesson for today i
  • 00:25:53
    will talk to you later
  • 00:25:55
    bye
Tags
  • mutations génétiques
  • somatiques
  • germinales
  • substitutions
  • insertions
  • suppressions
  • effets des mutations
  • mutagènes
  • ADN
  • protéines