Gene control — common mistakes

The lac operon is a critical example of gene control in prokaryotes (bacteria), demonstrating how genes for lactose metabolism are switched on or off depending on the presence of lactose and glucose. It's frequently tested in Cambridge 9700 Biology Paper 4, so understanding its structure and regulatory mechanisms (repressor, cAMP, CAP) is vital. You can find detailed explanations and practice questions in our free course, alongside relevant past papers to master this concept.

Epigenetic modifications are crucial for differential gene expression in eukaryotes, dictating cell specialisation and development. Histone acetylation generally loosens chromatin, making DNA accessible and increasing gene expression. DNA methylation, conversely, often condenses chromatin or blocks transcription factor binding, leading to gene silencing. Our premium lessons cover these complex mechanisms thoroughly, and you can test your understanding with past papers available on our site.

Transcription factors are proteins that bind to specific DNA sequences (promoters, enhancers, silencers) to activate or repress gene transcription, acting as master switches. MicroRNAs (miRNAs) are small non-coding RNAs that regulate gene expression post-transcriptionally, either by degrading target mRNA or inhibiting its translation. Both are key components of eukaryotic gene control and are frequently assessed in 9700 Biology. Explore our free course for in-depth explanations and tackle past papers to solidify your knowledge.