Explain how the binding of a transcription factor to an enhancer sequence can increase the rate of transcription of a distant gene.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
Enhancers are non‑coding regulatory DNA sequences that can be located far from the gene they regulate (upstream, downstream, or within an intron). A specific transcription factor (activator protein) binds to the enhancer sequence via its DNA‑binding domain. DNA looping brings the enhancer‑bound transcription factor into physical proximity with the promoter region / transcription initiation complex. Interaction between the transcription factor and the transcription initiation complex / RNA polymerase II stabilises or recruits the polymerase, increasing the rate of transcription initiation.
Examiner tips
- Use the exact terms ‘enhancer’, ‘transcription factor’, ‘DNA looping’, ‘promoter’, ‘RNA polymerase II’.
- Show the sequence of events: binding → looping → recruitment/stabilisation.
- Keep the answer concise – 4 points, one sentence each.
- Mention that the enhancer can be far from the gene to justify the looping step.
Common mistakes
- Confusing enhancers with promoters or silencers.
- Omitting the DNA‑binding domain of the transcription factor.
- Failing to explain the looping mechanism or the role of RNA polymerase II.
Mark scheme (4 marks)
- Enhancers are non-coding regulatory DNA sequences that can be located far from the gene they regulate (upstream, downstream, or within an intron).
- A specific transcription factor (activator protein) binds to the enhancer sequence via its DNA-binding domain.
- DNA looping brings the enhancer-bound transcription factor into physical proximity with the promoter region / transcription initiation complex.
- Interaction between the transcription factor and the transcription initiation complex / RNA polymerase II stabilises or recruits the polymerase, increasing the rate of transcription initiation.
Key terms in this question
enhancer · transcription factor
Related
- All IB DP Biology Higher Level (2023 syllabus) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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