A student learns that a mutation in a gene can sometimes result in a non-functional protein being made. Explain how a change in the base sequence of a gene can lead to a different protein being produced.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Proteins are made using information stored in DNA. The sequence of bases in a gene acts as a code that is used during protein synthesis to join amino acids in a specific order.
Model answer (5 marks)
DNA contains a sequence of bases that codes for a specific sequence of amino acids
A mutation changes the base sequence of the gene
The altered base sequence is transcribed into mRNA, producing a different mRNA sequence
The altered mRNA is translated at the ribosome, causing a different amino acid to be added
A different sequence of amino acids results in a different‑shaped (tertiary) structure / non‑functional protein
A mutation changes the base sequence of the gene
The altered base sequence is transcribed into mRNA, producing a different mRNA sequence
The altered mRNA is translated at the ribosome, causing a different amino acid to be added
A different sequence of amino acids results in a different‑shaped (tertiary) structure / non‑functional protein
Examiner tips
- Use the exact terminology: mutation, transcription, translation, amino acid, tertiary structure
- Show the chain: DNA → mRNA → protein
- Explain that a single base change can alter one codon, changing one amino acid
Common mistakes
- Confusing DNA with mRNA in the explanation
- Lacking the step that the altered mRNA is translated
- Not linking the amino acid change to a change in protein shape
Mark scheme (5 marks)
- DNA contains a sequence of bases that codes for a specific sequence of amino acids
- A mutation changes the base sequence of the gene
- The altered base sequence is transcribed into mRNA, producing a different mRNA sequence
- The altered mRNA is translated at the ribosome, causing a different amino acid to be added
- A different sequence of amino acids results in a different-shaped (tertiary) structure / non-functional protein
Key terms in this question
Related
- All Pearson Edexcel A-Level Biology A (9BI0) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
More DNA, RNA and protein synthesis questions
- A cell in the pancreas produces the protein insulin. Describe the roles of DNA, …
- A scientist compares the base sequence of a gene in a cell's nucleus with the ba…
- Describe how a molecule of messenger RNA (mRNA) is produced from a gene, and exp…
- Explain how the sequence of bases in a gene determines the sequence of amino aci…