# Explain how the formation of peptide bonds and subsequent folding of a polypeptide leads to a protein with a specific three-dimensional shape.

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

## Mark scheme (4 marks)

1. Peptide bonds form by condensation reactions between the amino group of one amino acid and the carboxyl group of another, releasing water.
2. The sequence of amino acids (primary structure) is determined by the gene / sequence of codons, and this sequence determines how the polypeptide will fold.
3. Hydrogen bonds between amino acids in the polypeptide backbone produce secondary structures such as alpha helices or beta-pleated sheets.
4. Further folding into a specific tertiary (and quaternary) structure is stabilised by interactions between R-groups, including hydrogen bonds, ionic bonds, disulfide bridges, and hydrophobic interactions.

## Key terms

- [peptide bond](https://www.gradenine.co.uk/glossary/peptide-bond)

## Related

- [Revision notes for IB DP Biology Standard Level (2023 syllabus)](https://www.gradenine.co.uk/learn)
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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-the-formation-of-peptide-ace20e3f) · Published by Druglandscape Ltd.