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today we're going to be talking about
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the only two types of nucleic acids that
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exist
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dna
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and rna
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dna stands for
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deoxyribonucleic acid
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and rna stands for ribonucleic acid
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as nucleic acids both dna and rna are
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long organic macro molecules which means
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they are very large molecules that
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contain the element carbon
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both dna and rna are composed of nucleic
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acid monomers called nucleotides
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nucleotide monomers always contain
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a phosphate group
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a five carbon sugar sometimes referred
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to as a pentose
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and a nitrogenous base
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but
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dna nucleotides have the five carbon
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sugar
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deoxyribose while rna has a different
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five carbon sugar called ribose
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the pentose sugar in dna has one less
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oxygen than ribose in rna which leads to
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its name deoxyribose
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let's focus on the nitrogenous bases in
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dna for a moment
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each dna nucleotide contains only one of
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four possible nitrogenous bases
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adenine
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guanine
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thymine and cytosine
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these four bases are usually abbreviated
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a
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g
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t
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and c
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when nucleotide bases connect through
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hydrogen bonds it's important to know
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that the bases always pair up with the
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same partners
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adenine only pairs with thymine
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and guanine only pairs with cytosine
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this is called the base pair rule
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scientists classify nitrogenous bases
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according to the shape of their
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molecules
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adenine and guanine both have a double
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ring structure containing a six membered
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and a five-membered nitrogen-containing
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ring fused together
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these types of ring structures are
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chemically classified as purines
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but thymine and cytosine both only have
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a single six-membered
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nitrogen-containing ring shape so they
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are chemically classified as pyrimidines
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here's a little hint to help you
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remember this
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pyrimidine has a y in its name and so do
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the bases classified as pyrimidines
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thymine and cytosine
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like dna an rna nucleotide may have the
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nitrogenous bases adenine guanine or
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cytosine
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but unlike dna which has the nitrogenous
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base thymine
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rna has the nitrogenous base uracil
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instead
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this means that any nucleic acid that
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contains thymine must be a strand of dna
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and that any nucleic acid that contains
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uracil must be a piece of rna
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like thymine uracil has a single
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nitrogen-containing ring so it would
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also be classified as a pyrimidine
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so what do the nitrogenous bases have to
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do with building a dna molecule
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well
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each strand of dna begins to assemble
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when the phosphate group in one
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nucleotide bonds with the five carbon
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sugar in another nucleotide
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the two strands that make up a dna
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molecule are linked through hydrogen
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bonds between their nitrogenous bases
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when the spiral dna molecule is
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untwisted
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these base pairs look like rungs on a
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ladder
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the spiral dna molecule is described as
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having a double helix shape
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james watson and francis crick first
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described dna's double-stranded helical
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structure in 1953
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after looking at x-ray images of a dna
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molecule taken by rosalind franklin
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now let's look at the structure of rna
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and see how it compares to the structure
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of dna
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while dna is a double-stranded molecule
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rna is always single stranded
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in eukaryotic cells dna is found only in
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the nucleus
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but rna can be found in the cytoplasm as
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well as in the nucleus
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dna controls heredity by containing the
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code or set of instructions for building
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the functional and structural proteins
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that make up your body
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and rna uses these varied instructions
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to build all the proteins a living
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organism needs
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there are three types of rna
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messenger rna referred to as mrna
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ribosomal rna referred to as rrna
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and transfer rna referred to as trna
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messenger rna starts off in a cell's
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nucleus
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here it transcribes or copies the
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instructions for assembling a protein
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from a portion of the cell's dna
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next the messenger rna takes these
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instructions or protein recipe to a
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ribosome in the cytoplasm
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the ribosome which is made out of
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ribosomal rna and proteins is the site
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where this recipe is read and translated
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into a protein
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finally transfer rna in the cytoplasm
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brings specific amino acids to the
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ribosome so that the particular protein
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encoded by the recipe can be made
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we'll cover more detail about the way
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dna and rna make proteins in another
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video
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to sum up
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dna and rna are the only two nucleic
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acids that exist
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both dna and rna are built from nucleic
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acid monomers called nucleotides
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nucleotides always contain a phosphate
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group of five carbon sugar and a
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nitrogenous base
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deoxyribose
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is the sugar in dna
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and ribose is the sugar in rna
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the nitrogenous bases in dna are adenine
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thymine cytosine and guanine
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the nitrogenous bases in rna are adenine
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uracil
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cytosine and guanine
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in dna
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adenine always pairs together with
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thymine
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and cytosine always pairs together with
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guanine
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adenine and guanine are purines
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cytosine thymine and uracil are
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pyrimidines
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dna is composed of two strands linked
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through hydrogen bonds between their
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nitrogenous bases
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the two dna strands are twisted into a
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double helix shape first identified by
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watson and crick
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rna is a single stranded molecule
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in cells
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dna is found only in the nucleus while
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rna is found in the cytoplasm as well as
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the nucleus
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dna controls heredity by containing the
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instructions for building the proteins
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that make up an organism and allow it to
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function
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rna uses these instructions to build
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proteins
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there are three types of rna
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messenger rna ribosomal rna and transfer
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rna messenger rna copies the
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instructions for building a protein and
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takes them to a ribosome
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ribosomal rna is the site where the
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instructions are translated into a
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protein
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transfer rna brings specific amino acids
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to the ribosome so the correct proteins
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can be made
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[Music]
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[Music]
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you
