Explain how transcription factors regulate eukaryotic genes
Describe transcription factors as proteins binding DNA to increase or decrease transcription rate.
A Level; Cambridge International Biology 9700, 2028–2030. Written answers are self-checked; this is not practical-skills certification.
Before you begin
- Genes are DNA sequences that can be inherited; meiosis and fertilisation link parental genomes.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
What can transcription factors change?
What you will learn
- State that transcription factors are proteins that bind to DNA
- Explain how transcription factors can increase or decrease eukaryotic transcription
Original teaching model. Counts and records are stipulated; drawings are schematic.
| Feature | Meaning |
|---|---|
| Containing structure | Nucleus |
| DNA-bearing structure | Chromosome |
| Selected region | Protein-coding gene |
| Evidence limit | An enlarged view does not add a chromosome |
Build the genetic explanation
Transcription factors are proteins that bind specific DNA sequences and regulate gene expression in eukaryotes. Some promote transcription by helping RNA polymerase or associated proteins assemble at a gene; others reduce transcription by blocking access or interfering with the transcription machinery. Their action changes the rate of transcription, which affects the amount of mRNA and potentially the protein produced.
Check the evidence and limits
A transcription factor does not change the DNA base sequence. Binding can increase or decrease transcription depending on the factor and regulatory context.
Pause and explain
A protein binds a promoter region but has no effect on transcription rate. Can it be called an effective transcriptional regulator in this context? Explain.
Worked example
A DNA-binding protein increases transcription of a target gene. What type of regulator is it?
Show the worked solution
- It is a protein that binds DNA.
- It increases transcription rate.
Answer It is an activating transcription factor.
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Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Explain how a transcription factor can increase the amount of protein made from a gene.
Give me a hint
Set out the alleles or steps before deciding the outcome.
Compare my reasoning
- It binds regulatory DNA.
- Increased transcription produces more mRNA for translation.
A transcription factor binds DNA and increases transcription. More mRNA can then be available for translation, potentially increasing protein production.
Look for these in your work
- Genetic terms used correctly
- Steps linked
A repressor transcription factor binds DNA and transcription decreases. What changed, and what did not?
Give me a hint
Use the given evidence and state your assumptions.
Compare my reasoning
- The transcription rate changed.
- The nucleotide sequence need not change.
Gene expression decreased because transcription was reduced. The DNA base sequence itself need not have changed.
Look for these in your work
- Prediction or interpretation supported
- Limits stated
A protein binds a promoter region but has no effect on transcription rate. Can it be called an effective transcriptional regulator in this context? Explain.
Give me a hint
Apply the inheritance or gene-control model to the new context.
Compare my reasoning
- Binding alone is not the whole effect.
- The definition also involves changing expression rate.
It binds DNA but there is no evidence that it regulates transcription in this context, because no change in transcription rate is observed.
Look for these in your work
- Model applied accurately
- Unsupported certainty avoided
Common mistakes
- Calling a transcription factor an enzyme that translates mRNA
- Claiming binding changes the gene’s nucleotide sequence
What can you explain now?
What can transcription factors change?
Compare with the explanation
The rate of transcription
They bind DNA and regulate transcription up or down.
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Make it stick
How can transcription factors raise or lower gene expression?
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