A student learns that a mutation in a gene can change the protein that a cell produces. Explain how a gene controls the production of a specific protein, and suggest how a mutation in the gene could affect the protein produced.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Proteins are made inside cells using genetic information stored in DNA. A change to this information can alter the protein that is made.
Model answer (5 marks)
A gene is a segment of DNA that contains the codons for a particular amino‑acid sequence. During transcription, the DNA sequence is copied into mRNA, which is transported out of the nucleus to the ribosome. At the ribosome, translation reads the mRNA codons and links the corresponding amino acids in the correct order, producing a specific protein.
A mutation is a random change in the DNA base sequence of a gene. If the mutation alters a codon, the amino‑acid sequence of the protein may change. This can give a non‑functional or altered protein, or in some cases the protein may remain unchanged (a neutral mutation).
A mutation is a random change in the DNA base sequence of a gene. If the mutation alters a codon, the amino‑acid sequence of the protein may change. This can give a non‑functional or altered protein, or in some cases the protein may remain unchanged (a neutral mutation).
Examiner tips
- Use the terms ‘gene’, ‘transcription’, ‘mRNA’, ‘translation’, ‘ribosome’, and ‘mutation’.
- Show the flow: DNA → mRNA → protein.
- Explain that a mutation can change the amino‑acid sequence or have no effect.
Common mistakes
- Confusing transcription with translation.
- Forgetting that a mutation may be silent (no change in protein).
- Using vague language like ‘change the protein’ without linking to amino‑acid sequence.
Mark scheme (5 marks)
- A gene is a section of DNA that codes for a specific amino acid sequence
- mRNA carries the genetic information from the nucleus to the ribosomes (transcription)
- At the ribosomes, the amino acids are joined together in the correct sequence to make a specific protein (translation)
- A mutation is a random change in the DNA / base sequence of the gene
- A mutation can change the amino acid sequence, so a different (non-functional / altered) protein may be produced — or the protein may be unchanged (neutral effect)
Key terms in this question
Related
- All OCR A-Level Biology B — Advancing Biology (H422) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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