Proteins are large biological molecules made up of amino acids joined together by peptide bonds. Explain how the structure of a protein is related to its function, referring to the sequence of amino acids and the role of bonds in maintaining the protein's shape.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Enzymes are proteins that act as biological catalysts. Each enzyme has a specific active site that allows it to bind to only one type of substrate molecule.
Model answer (5 marks)
1. The order of amino acids gives the primary structure of a protein.
2. This sequence determines how the chain folds into secondary and tertiary structures, giving the protein a specific three‑dimensional shape.
3. Bonds such as hydrogen bonds, ionic interactions, van der Waals forces and disulfide bridges maintain this shape.
4. The active site of an enzyme is a precise part of this shape, so only a substrate with a complementary structure can bind.
5. A change in the amino‑acid sequence or denaturation that alters the shape destroys the active site and the protein loses its function.
2. This sequence determines how the chain folds into secondary and tertiary structures, giving the protein a specific three‑dimensional shape.
3. Bonds such as hydrogen bonds, ionic interactions, van der Waals forces and disulfide bridges maintain this shape.
4. The active site of an enzyme is a precise part of this shape, so only a substrate with a complementary structure can bind.
5. A change in the amino‑acid sequence or denaturation that alters the shape destroys the active site and the protein loses its function.
Examiner tips
- Use the exact terms from the mark scheme (primary, secondary, tertiary, hydrogen bonds, disulfide bonds).
- Show the logical sequence: sequence → shape → function.
- Mention that a change in sequence or denaturation breaks the shape and function.
Mark scheme (5 marks)
- The sequence (order) of amino acids determines the primary structure of the protein
- The sequence of amino acids determines how the protein folds / the three-dimensional shape of the protein
- Bonds (e.g. hydrogen bonds / other intermolecular forces / disulfide bonds) hold the protein in its specific shape
- The specific shape of the active site of an enzyme (protein) means only a complementary substrate can bind
- If the sequence of amino acids changes / the protein unfolds (denatures), the shape changes and the protein can no longer carry out its function
Key terms in this question
Related
- All Eduqas A-Level Chemistry revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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