Describe how the order of bases in a gene determines which protein is made during protein synthesis.

WJEC GCSE Biology (Wales) — 2.4.1 Variation · Describe · 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 section of DNA made up of a sequence of bases (A, T, C, G). Every three bases (a codon) codes for one amino acid. The order of the codons therefore determines the sequence of amino acids in the protein. The sequence of amino acids dictates the protein’s structure and hence its type and function.

Examiner tips

Use the word ‘codon’ when referring to a triplet of bases.
Show the logical chain: DNA sequence → codons → amino acids → protein structure.
Mention that the sequence is read 5’→3’ during transcription.
Avoid unnecessary detail such as RNA intermediates unless asked.

Common mistakes

Confusing DNA bases with RNA bases (T vs U).
Saying ‘the gene determines the protein’ without explaining the codon‑amino acid link.
Using vague terms like ‘order’ without specifying codons or amino acids.

Mark scheme (4 marks)

A gene is a section of DNA made up of a sequence of bases / nucleotides
Every three bases (a triplet) codes for one amino acid
The sequence of bases determines the sequence of amino acids in the protein
The sequence of amino acids determines the structure / type of protein produced

Key terms in this question

gene · bases · protein synthesis