Explain why two different proteins can both be made from the same twenty amino acids, yet have completely different shapes and functions in the body.

Eduqas A-Level Chemistry — 4.7 Amino acids, peptides and proteins · Explain · 5 marks · View as Markdown

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

Model answer (5 marks)

1. The twenty standard amino acids can be arranged in many different orders.
2. These amino acids are linked by peptide bonds to form a linear polypeptide chain.
3. The polypeptide chain then folds into a specific three‑dimensional structure.
4. Different amino‑acid sequences give rise to different folding patterns and therefore different structures.
5. The unique three‑dimensional shape of a protein determines its specific function in the body.

Examiner tips

  • Use the word ‘sequence’ to show you understand the importance of order. Show the chain‑to‑fold progression. Mention that structure = function. Keep each point concise and use exam‑style terminology.

Common mistakes

  • Confusing the number of amino acids with the number of possible proteins. Failing to mention peptide bonds. Saying ‘shape’ without linking it to function.

Mark scheme (5 marks)

  1. The sequence (order) of amino acids in a protein can vary
  2. Amino acids are joined by peptide bonds to form a chain (polypeptide)
  3. The chain folds into a specific three-dimensional shape
  4. Different sequences produce different shapes/structures
  5. The specific shape of a protein determines its function

Key terms in this question

amino acids

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