OCR AS Biology Nucleic Acids Notes

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  • Created on: 19-05-13 14:43
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Nucleic Acids
a) State that deoxyribose nucleic acid (DNA) is a polynucleotide, usually
double stranded, containing the nucleotide bases, adenine, thymine,
cytosine and guanine
A nucleotide is composed of:
- phosphate group
- Deoxyribose sugar (pentose sugar)
- Nitrogenous Base
4 different bases:
- Adenine
- Thymine
- Cytosine
- Guanine
Double stranded (helix)
Condensation reaction between sugar + phosphate groups =
forms covalent bonds
Purines (double ring structure) ­ Adenine + Guanine
Pyrimidine (single ring structure) ­ Thymine + Uracil +
B) State that ribonucleic acid (RNA) is a
polynucleotide, usually single
stranded, compose of bases, adenine,
uracil, cytosine and guanine
Ribose sugar
Single stranded
4 different bases:
- Adenine
- Uracil
- Cytosine
- Guanine

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C) Describe how hydrogen bonding between complementary base pairs (A-T
and C-G) on two antiparallel DNA polynucleotides leads to the formation of a
DNA molecule and how the twisting of DNA forms a double helix shape
Adenine ­ thymine (2 hydrogen
Guanine ­ Cytosine (3 hydrogen
RNA = Adenine ­ Uracil (2 hydrogen
Hydrogen bonds between bases
Covalent bonds between sugar ­
Anti-parallel helix
D) Outline how DNA replicates semi-conservatively with the role of DNA
DNA replication
Double helix unzips…read more

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E) State that a gene is a sequence of DNA nucleotides that codes for a
Gene ­ a length of DNA that codes
for one or more polypeptides
The sequence of bases on DNA are
code instructions for proteins, they
code for the amino acid sequence
present in the protein
F) Outline the roles of DNA & RNA in living organisms, including the concept of
protein synthesis
3 forms of RNA
Messenger RNA (mRNA) ­ is a strand made complementary to a strand of…read more

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RNA (codon)
tRNA bring amino acids (anti-codon) which then complementary bind 3 at a time via rRNA ­
this is translation
second rRNA bonds via 3 exposed bases
the amino acids form peptide bonds, catalysed by peptidyl transferase
process repeats until polypeptide is formed…read more


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