Explain why amino acids are described as monomers, and explain how the body produces amino acid monomers from the protein in food.

AQA A-Level Biology (7402) — 3.1.1 Monomers and Polymers · Explain · 5 marks · View as Markdown

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

Model answer (5 marks)

Amino acids are the small, basic units that make up proteins.
They link together via peptide bonds to form a polymer – the protein.
Proteins in food are first broken down during digestion.
Enzymes such as pepsin, trypsin and chymotrypsin catalyse this breakdown.
Water molecules are added (hydrolysis) to break the peptide bonds, releasing free amino‑acid monomers.

Examiner tips

  • Use the term ‘monomer’ and ‘polymer’ clearly. Show the role of enzymes and water in hydrolysis. Keep the answer concise – 5 points, one sentence each.

Common mistakes

  • Confusing proteins with amino acids. Omitting the hydrolysis step. Using vague terms like ‘break down’ without mentioning enzymes or water.

Mark scheme (5 marks)

  1. Amino acids are the smaller/basic units from which proteins are built
  2. Amino acids join together to form a polymer (protein)
  3. Protein in food is broken down / digested
  4. Enzymes catalyse the breakdown of protein
  5. Water molecules are used / added to break the bonds between amino acids (hydrolysis)

Key terms in this question

monomer · amino acid

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