Explain how proteins are able to carry out such a diverse range of functions within living organisms.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Proteins are the most structurally diverse biological macromolecules, performing roles including catalysis, transport, defence, and structural support.
Model answer (4 marks)
Proteins can perform many functions because the 20 different amino acids can be arranged in any sequence, giving a huge variety of polypeptides. The unique sequence of amino acids determines the protein’s specific tertiary (three‑dimensional) structure through interactions between the R groups. This 3‑D shape gives the protein a particular surface that can bind precisely to other molecules – for example a substrate in an enzyme, a ligand on a receptor or an antigen on a cell surface – so the protein can carry out a specific function. In addition, proteins may be fibrous or globular and may be composed of several polypeptide subunits (quaternary structure), further expanding the range of possible shapes and roles.
Examiner tips
- Use the word ‘sequence’ to link amino acids to structure; mention tertiary structure; give an example of a functional interaction; note fibrous/globular and quaternary structure for extra marks.
Common mistakes
- Confusing primary sequence with tertiary structure; forgetting to mention the 20 amino acids; not giving an example of a functional interaction; ignoring fibrous/globular or quaternary structure aspects.
Mark scheme (4 marks)
- There are 20 different amino acids that can be combined in any sequence, giving an enormous variety of possible polypeptides.
- The unique sequence of amino acids determines the specific tertiary / three-dimensional structure of each protein through interactions between R groups.
- The specific three-dimensional shape of a protein determines its function, as it allows the protein to interact precisely with other molecules (e.g. substrate, receptor, antigen).
- Proteins can also be fibrous or globular, and can be formed from multiple polypeptide subunits (quaternary structure), extending the range of possible structures and functions.
Related
- All IB DP Biology Standard Level (2023 syllabus) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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