9700 · 6.1
Structure of nucleic acids and replication of DNA — FAQ
Frequently asked questions for 9700 Structure of nucleic acids and replication of DNA. Direct answers first, then deeper explanation — then practise with marking.
What are the key differences between DNA and RNA for Cambridge 9700 Biology?
The main differences are in their sugar components (deoxyribose in DNA, ribose in RNA), one of their nitrogenous bases (thymine in DNA, uracil in RNA), and their typical structure (double-stranded in DNA, single-stranded in RNA). Mastering these distinctions is crucial for Paper 1 multiple choice and Paper 2 structured questions.
How does DNA replication ensure genetic continuity?
DNA replication is semi-conservative, meaning each new DNA molecule formed consists of one original (parental) strand and one newly synthesised strand. This mechanism, coupled with the precise complementary base pairing and proofreading by DNA polymerase, ensures that genetic information is accurately copied and passed on faithfully to daughter cells during cell division, thus maintaining genetic continuity.
Why is DNA replication described as semi-conservative?
Each new DNA molecule keeps one of the two original strands and builds one new strand against it. The double helix unwinds as hydrogen bonds between the bases are broken, each parental strand acts as a template, free nucleotides line up by complementary base pairing (A with T, C with G), and DNA polymerase joins them with phosphodiester bonds. Every daughter molecule is therefore half old and half new — which Meselson and Stahl demonstrated with DNA labelled with the heavy isotope ¹⁵N.