# Proteins are made from chains of amino acids. A student tests two food samples for the presence of protein using the Biuret test. Sample A gives a colour change from blue to violet. Sample B remains blue. Explain what the results of the Biuret test tell the student about the two food samples, and describe the role that amino acids play in forming a functional enzyme.

> Eduqas A-Level Biology — 1.1 Chemical elements and biological molecules · Explain · 5 marks

> The Biuret test detects the presence of peptide bonds. Amino acids join together and fold to form protein molecules, including enzymes.

## Mark scheme (5 marks)

1. Sample A contains protein / peptide bonds are present in Sample A
2. Sample B does not contain protein / no peptide bonds present in Sample B
3. Amino acids join / bond together to form chains that make up a protein / enzyme
4. The chain of amino acids folds to form a specific three-dimensional shape / active site
5. The active site has a complementary shape to the specific substrate, allowing the enzyme to function / form an enzyme-substrate complex

## Key terms

- [Biuret test](https://www.gradenine.co.uk/glossary/biuret-test)
- [amino acids](https://www.gradenine.co.uk/glossary/amino-acids)

## Related

- [Revision notes for Eduqas A-Level Biology](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)

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Source: [GradeNine](https://www.gradenine.co.uk/q/proteins-are-made-from-chains-of-dc6bf63d) · Published by Druglandscape Ltd.