Amino acids can join together by condensation polymerisation to form polypeptides. Explain what is meant by the terms 'condensation polymerisation' and 'polypeptide', and state what type of molecules make up DNA.

AQA A-Level Chemistry (7405) — 3.3.13 Amino acids, proteins and DNA (A-Level only) · Explain · 5 marks · View as Markdown

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

Model answer (5 marks)

Condensation polymerisation is a process in which monomers join together to form a polymer, with the loss of a small molecule such as water. It requires monomers that possess two reactive functional groups.
A polypeptide is a polymer chain composed of amino acids linked by peptide bonds.
DNA is made up of nucleotides as its monomer units.

Examiner tips

  • Use the exact terms ‘condensation polymerisation’, ‘polypeptide’, and ‘nucleotides’. Show the loss of water in the polymerisation step. Mention the two functional groups on the monomers (amine and carboxyl).

Common mistakes

  • Confusing condensation with addition polymerisation. Forgetting to state that water is released. Using ‘protein’ instead of ‘polypeptide’ or omitting the definition of DNA monomers.

Mark scheme (5 marks)

  1. Condensation polymerisation involves monomers joining together to form a polymer
  2. During condensation polymerisation, a small molecule (such as water) is lost/released
  3. Condensation polymerisation requires monomers with two functional groups
  4. A polypeptide is a chain of amino acids
  5. DNA is made from nucleotides (as its monomers)

Key terms in this question

condensation polymerisation · polypeptide · amino acids

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