9700 · 16.1
Common exam mistakes on 9700 Passage of information from parents to offspring. Learn what loses marks, then practise the topic with Examiner’s Ink.
When describing DNA replication or protein synthesis, remember to use specific enzyme names (e.g., DNA helicase, DNA polymerase, RNA polymerase, DNA ligase) and describe their precise functions. Clarity on base pairing rules (A-T/U, G-C) is also paramount, and ensure you specify the directionality (5' to 3' or 3' to 5') of strands when relevant.
DNA stores the genetic instructions for developing and functioning, acting as the blueprint passed from parents to offspring. It ensures the continuity of traits and biological information across generations. For a deeper dive into this and other topics, explore our free 9700 biology course and tackle past paper questions to solidify your understanding.
DNA replication occurs semi-conservatively, meaning each new DNA molecule consists of one original (template) strand and one newly synthesised strand. Enzymes like DNA helicase unwind the double helix, and DNA polymerase adds complementary nucleotides to each separated strand, ensuring high fidelity in copying the genetic information. The process involves continuous synthesis on the leading strand and discontinuous synthesis (via Okazaki fragments and DNA ligase) on the lagging strand.
Transcription is the process where a gene's DNA sequence is copied into an RNA molecule (mRNA) in the nucleus of eukaryotic cells. This is followed by post-transcriptional modification (splicing, capping, tailing). Translation is the process where the mature mRNA sequence is used to synthesise a protein on ribosomes in the cytoplasm. Essentially, transcription makes RNA from a DNA template, while translation uses that RNA template to make a polypeptide chain (protein).
The lac operon is a classic example of gene regulation in prokaryotes like E. coli. It's a cluster of genes responsible for lactose metabolism that can be switched on or off depending on the presence of lactose. It demonstrates how cells can efficiently control gene expression to produce proteins only when they are needed, conserving energy and resources.