# Amino acids are the building blocks of proteins. Explain why amino acids can act as both acids and bases in aqueous solution, and state the name of the bond formed when two amino acids join together.

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

> Glycine is a simple amino acid. Its structure contains both an amine group (–NH₂) and a carboxylic acid group (–COOH) on the same molecule.

## Mark scheme (5 marks)

1. The carboxylic acid group (–COOH) can donate a proton / H⁺ ion
2. This allows the amino acid to act as an acid
3. The amine group (–NH₂) can accept a proton / H⁺ ion
4. This allows the amino acid to act as a base
5. The bond formed when two amino acids join together is called a peptide bond

## Key terms

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

## 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)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

---
Source: [GradeNine](https://www.gradenine.co.uk/q/amino-acids-are-the-building-blocks-7e933ee1) · Published by Druglandscape Ltd.