# Describe how a molecule of messenger RNA (mRNA) is produced from a gene, and explain how ribosomes use this mRNA to assemble a polypeptide chain.

> Pearson Edexcel A-Level Biology A (9BI0) — 1.4 DNA, RNA and protein synthesis · Describe and Explain · 5 marks

> Protein synthesis occurs in two main stages: transcription and translation. Both stages rely on complementary base pairing.

## Mark scheme (5 marks)

1. The double helix of DNA unwinds / the two strands of the gene separate
2. Free RNA nucleotides align along the template strand by complementary base pairing, forming the mRNA strand (transcription)
3. The mRNA molecule leaves the nucleus through a nuclear pore and travels to a ribosome
4. The ribosome reads the mRNA in groups of three bases (codons) / transfer RNA (tRNA) molecules bring specific amino acids to the ribosome
5. Amino acids are joined together in a specific sequence (determined by the mRNA base sequence) to form a polypeptide chain (translation)

## Key terms

- [mRNA](https://www.gradenine.co.uk/glossary/mrna)
- [ribosome](https://www.gradenine.co.uk/glossary/ribosome)
- [polypeptide](https://www.gradenine.co.uk/glossary/polypeptide)

## Related

- [Revision notes for Pearson Edexcel A-Level Biology A (9BI0)](https://www.gradenine.co.uk/learn)
- [How to answer "Describe and 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/describe-how-a-molecule-of-messenger-1312c911) · Published by Druglandscape Ltd.