# Explain how two amino acid molecules react together to form a dipeptide, and describe the type of bond formed between them.

> Edexcel A-Level Chemistry (9CH0) — 18.2 Amines, amides and amino acids · Explain · 5 marks

> Amino acids contain both an amine group (–NH₂) and a carboxylic acid group (–COOH). When two amino acids react together, a dipeptide is formed along with a small molecule as a by-product.

## Mark scheme (5 marks)

1. The –COOH group of one amino acid reacts with the –NH₂ group of the other amino acid
2. Water is eliminated / lost as a by-product during the reaction
3. The reaction is described as a condensation reaction
4. The bond formed between the two amino acids is called a peptide bond
5. The peptide bond is formed between the carbon of the –CO– and the nitrogen of the –NH– group, linking the two amino acid residues

## Key terms

- [amino acid](https://www.gradenine.co.uk/glossary/amino-acid)
- [dipeptide](https://www.gradenine.co.uk/glossary/dipeptide)

## Related

- [Revision notes for Edexcel A-Level Chemistry (9CH0)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-two-amino-acid-molecules-c3b67abf) · Published by Druglandscape Ltd.