DNA - AS OCR Biology

My notes on DNA for the Unit 2 AS OCR Biology exam. Hope they are of help!!

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Nucleic Acids: DNA
The monomers of nucleic acids are called
nucleotides , they are made up of a:
phosphate group , chemically
reactive as involved in linking
nucleotides in condensation
pentose sugar , deoxyribose (DNA) or
ribose (RNA), also chemically
nitrogenous base , either double
ringed purine (adenine, guanine) or
single ringed pyramidine (cytosine, thymine (DNA) or uracil (RNA))
Nucleotides joined together in a sugar-phosphate backbone by covalent
phosphodiester bonds formed in condensation reactions to make
Excess purines are broken down into uric acid in liver
and excreted in the urine. Uric acid is insoluble at
lower temperatures so form crystals that are
depositied in joints at the extremities if too much uric
acid is in the blood. This is known as g out .
Deoxyribosenucleic acid (DNA) is a
polynucleotide, usually double stranded,
which is made up of nucleotides
containing the bases adenine, guanine,
cytosine and thymine.
The sugar phosphate backbones are
anti-parallel to each other so that the bases
of each strand project towards each
other. The bases are joined by hydrogen
bonds however, adenine will only bond with
thymine by two hydrogen bonds, and guanine will only bond with cytosine by
three hydrogen bonds. This is called c omplementary base pairing. The two
strands of DNA then twist together to form a double helix.
Semi conservative replication
The DNA strands untwist and unzip as D NA polymerase catalyses the
breaking of hydrogen bonds between the bases. Both strands then act
as a template and free DNA nucleotides align to each strand by
complementary base pairing i.e. purine to pyramidine. Hydrogen bonds
reform and a sugar-phosphate backbone between the free nucleotides
also form using covalent bonds. This is called s emi conservative
replication as one strand is from the parent molecule and the other is a
new strand.
Structure related to function:

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Sugar-phosphate backbone with covalent phosphodiester bonds give
Sequence of bases allows information to be stored and as DNA is a
long molecule, it can store large amounts of information
Complementary base pairing enables information to be replicated and
Double helix protects weak hydrogen bonds and makes the molecule
Hydrogen bonding allows chains to split for replication or transcription
and the many hydrogen bonds together give the molecule stability.…read more

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The amino acids are joined together by peptide bonds to
form a polypeptide with a specific primary structure. This process is called
translation.…read more


Caitlin x

This is amazing thank you

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