BiologyCode 9700
Structure of nucleic acids and replication of DNA
What this topic asks you to be able to do
- describe how nucleotides are built, including ATP as a phosphorylated nucleotide (structural formulae are not required)
- state that adenine and guanine are purines, whose molecules have two fused rings, whereas cytosine, thymine and uracil are pyrimidines, which have one ring (the bases' structural formulae are not expected)
- describe the form a DNA molecule takes as a double helix, including: why complementary base pairing matters where one strand runs 5′ to 3′ and its partner runs 3′ to 5′ (antiparallel), how hydrogen bonds differ between C–G and A–T pairs, and how nucleotides are joined through phosphodiester bonds
- describe semi-conservative DNA replication, as it happens in the S phase of the cell cycle, including: the jobs done by DNA ligase and DNA polymerase (you are not expected to know other enzymes of DNA replication in cells, or the different types of DNA polymerase), and why the lagging strand is replicated differently from the leading strand, given that DNA polymerase can add nucleotides only in a 5′ to 3′ direction
- describe how an RNA molecule is structured, taking messenger RNA (mRNA) as an illustration