A scientist extracts DNA from a sample of wheat cells. Explain how the structure of DNA allows it to carry the genetic information needed to produce different proteins.

AQA A-Level Biology (7402) — 3.4.1 DNA, Genes and Chromosomes · Explain · 5 marks · View as Markdown

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

Model answer (5 marks)

DNA is a polymer of nucleotides, each containing a base (A, T, C or G). The sequence of these bases in a gene determines the sequence of amino acids in a protein. Different genes have different base sequences, so they encode different amino‑acid chains. The amino‑acid sequence dictates the protein’s three‑dimensional shape, which in turn determines its function. Thus the DNA sequence carries the information needed to produce a variety of proteins.

Examiner tips

  • Use the exact terminology: polymer of nucleotides, bases A/T/C/G, gene sequence, amino‑acid sequence, protein structure and function.
  • Show the logical chain: DNA → base sequence → amino‑acid sequence → protein shape → function.
  • Keep the answer concise and directly address each point in the mark scheme.

Common mistakes

  • Confusing DNA bases with RNA bases (U instead of T).
  • Failing to link the amino‑acid sequence to protein shape and function.

Mark scheme (5 marks)

  1. DNA is made up of (repeating) nucleotides / DNA is a polymer of nucleotides
  2. Each nucleotide contains a base, and there are four different bases (A, T, C, G)
  3. The sequence / order of bases in a gene codes for a specific sequence of amino acids
  4. Different genes have different base sequences, so different amino acid sequences are produced
  5. The sequence of amino acids determines the shape / structure of the protein, which determines its function / different proteins are produced

Key terms in this question

gene · protein

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