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DNA and RNA - Biochemistry
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Here are lecture notes for a biochemistry lecture on DNA and RNA
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BIOCHEMISTRY – LECTURE FOUR PART ONEdna and rna
Nucleotides have a phosphate group, a five-carbon sugar (deoxyribose in DNA
and ribose in RNA) and a base (adenine, thymine, guanine and cytosine).
Nucleotides are connected to each other to form a long chain. They are joined by
phosphodiester bonds which form between the phosphate group of one
nucleotide (5’) and the 3’ -OH of the next nucleotide. The chain of nucleotides
has a 5’ to 3’ orientation.
Adenine and guanine are
purines whereas cytosine,
thymine and uracil are
pyrimidines. Purines always
bind with a pyrimidine. There
are three hydrogen bonds
between cytosine and guanine,
adenine and thymine have two.
The two DNA strands are
antiparallel one is 5’ to 3’ and
the other is 3’ to 5’ – this is
called directionality.
DNA – nucleotides connected by phosphodiester bonds, double helix made from
two polynucleotide strands connected by hydrogen bonds, polynucleotide
strands are complementary and genetic information is carried in the sequence of
nucleotides. Determining the 3D structure of DNA:
o Erwin Chargaff – determined that the amount of adenine = amount of
thymine, amount of cytosine = amount of guanine.
o Rosalind Franklin and Maurice Wilkins – performed x-ray diffraction studies
to identify the 3D structure, discovered that DNA is helical and discovered
the molecule has a diameter of 2nm and makes a complete turn of the
helix every 3.4nm.
o James Watson and Francis Crick – deduced the structure of DNA using
evidence from Chargaff, Franklin and others, proposed a double helix
structure.
o The double helix consists of 2 sugar-phosphate backbones, bases toward
the interior of the molecule which form hydrogen bonds with
complementary bases on the opposite backbone.
RNA forms a single strand but may pair up with itself. Some other nucleotides
are ATP – primary energy currency of the cell and NAD + and FAD – electron
carriers. ATP is adenosine triphosphate, it has ribose sugar, adenine base and
three phosphates.
There were three possible DNA replication methods that were considered –
conservative, semi-conservative and dispersive. Meselson and Stahl concluded
that the semi-conservative method was the correct mechanism. Replication
requires a template (parental DNA), enzymes to perform the copying and
building blocks (nucleotide triphosphates). It includes initiation – begins at an
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