Explain how different types of chemical bonds and interactions contribute to the tertiary structure of a protein.

IB DP Biology Standard Level (2023 syllabus) — B1.2 Proteins · Explain · 4 marks · View as Markdown

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

Model answer (4 marks)

Tertiary structure is the overall three‑dimensional folding of a single polypeptide chain.

Hydrogen bonds form between polar R groups (side chains), stabilising the folded structure.

Disulfide bonds/bridges form between the sulfur‑containing R groups of cysteine residues, providing covalent stabilisation.

Hydrophobic interactions cause non‑polar R groups to cluster in the interior of the protein, away from the aqueous environment, driving folding.

Examiner tips

Use the exact terminology: tertiary structure, hydrogen bonds, disulfide bonds, hydrophobic interactions. Show the four points in separate sentences or numbered points. Mention covalent vs non‑covalent bonds where relevant.

Common mistakes

Confusing secondary with tertiary structure. Omitting the role of disulfide bonds. Using vague terms like "folding" without specifying the types of bonds.

Mark scheme (4 marks)

Tertiary structure is the overall three-dimensional folding of a single polypeptide chain.
Hydrogen bonds form between polar R groups (side chains), stabilising the folded structure.
Disulfide bonds/bridges form between the sulfur-containing R groups of cysteine residues, providing covalent stabilisation.
Hydrophobic interactions cause non-polar R groups to cluster in the interior of the protein, away from the aqueous environment, driving folding.

Key terms in this question

tertiary structure