# 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

## Mark scheme (4 marks)

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

## Key terms

- [tertiary structure](https://www.gradenine.co.uk/glossary/tertiary-structure)

## Related

- [Revision notes for IB DP Biology Standard Level (2023 syllabus)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

---
Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-different-types-of-chemical-713afb89) · Published by Druglandscape Ltd.