A chromosome is described as a long, coiled molecule of DNA that carries genetic information in the form of genes. State what is meant by the term 'gene' and explain how the sequence of bases in a gene determines the specific protein produced in a cell.

Cambridge International IGCSE Biology (0610) — 17.1 Chromosomes, genes and proteins · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

A gene is a length of DNA that codes for the production of a specific protein.
The sequence of bases in the gene determines the sequence of amino acids in the protein.
Different sequences of amino acids produce proteins with different shapes.
Each protein has a specific shape that allows it to carry out a specific function.

Examiner tips

  • Use the exact wording from the mark scheme; include all four points.
  • Show the logical link: DNA → RNA → protein.
  • Mention that base sequence → codons → amino acids.
  • Keep the answer concise and in student voice.

Common mistakes

  • Mixing up DNA with RNA or protein in the definition of a gene.
  • Omitting the step that base sequence dictates amino acid sequence.
  • Using vague terms like ‘structure’ instead of ‘shape’ or ‘function’.

Mark scheme (4 marks)

  1. A gene is a length of DNA that codes for the production of a specific protein.
  2. The sequence of bases in the gene determines the sequence of amino acids in the protein.
  3. Different sequences of amino acids produce proteins with different shapes.
  4. Each protein has a specific shape that allows it to carry out a specific function.

Key terms in this question

gene · chromosome · sequence of bases · protein

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