# Explain how the sequence of bases in a gene determines the sequence of amino acids in a protein.

> Edexcel A-Level Biology A: Salters-Nuffield (9BN0) — 1.4 DNA, RNA and protein synthesis · Explain · 5 marks

> Protein synthesis occurs in two main stages: transcription in the nucleus and translation at the ribosome. The order of amino acids in a protein determines its shape and function.

## Mark scheme (5 marks)

1. DNA / gene contains a sequence of bases (that codes for a protein)
2. The sequence of bases in DNA is used as a template to make mRNA during transcription
3. mRNA carries the code out of the nucleus to the ribosome
4. At the ribosome, every three bases (a codon / triplet) on the mRNA codes for one amino acid
5. Amino acids are joined together in the order determined by the mRNA sequence to form a protein (translation)

## Key terms

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

## Related

- [Revision notes for Edexcel A-Level Biology A: Salters-Nuffield (9BN0)](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/explain-how-the-sequence-of-bases-13370fbc) · Published by Druglandscape Ltd.