# Explain how the sequence of amino acids in a polypeptide determines the three-dimensional shape of a globular protein.

> IB DP Biology Higher Level (2023 syllabus) — B1.2 Proteins · Explain · 4 marks

## Mark scheme (4 marks)

1. The primary structure (sequence of amino acids) is determined by the sequence of codons in the gene / mRNA.
2. Interactions between R groups of amino acids (e.g. hydrogen bonds, ionic bonds, disulfide bridges, hydrophobic interactions) cause the polypeptide to fold spontaneously.
3. Hydrophobic R groups are orientated towards the interior of the protein, away from the aqueous environment, stabilising the tertiary structure.
4. Because the sequence of R groups is fixed by the primary structure, a specific and unique three-dimensional conformation results, which determines the protein's function.

## Key terms

- [globular protein](https://www.gradenine.co.uk/glossary/globular-protein)

## Related

- [Revision notes for IB DP Biology Higher 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-the-sequence-of-amino-10217060) · Published by Druglandscape Ltd.