# A scientist compares the base sequence of a gene in a cell's nucleus with the base sequence of the messenger RNA (mRNA) produced from that gene. The scientist notices that the mRNA sequence is complementary to the template strand of the gene but is not identical to it. Explain why the mRNA sequence is complementary to the template strand, and describe what happens to the mRNA after it leaves the nucleus.

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

> Genes are found in the nucleus of a cell and are made of DNA. Messenger RNA (mRNA) is made using the gene as a template and carries the genetic code to the ribosomes.

## Mark scheme (5 marks)

1. mRNA is built by complementary base pairing with the template strand of the DNA
2. Each base on the template strand of DNA pairs with a specific complementary base (e.g. A pairs with U, C pairs with G) to form the mRNA
3. mRNA moves out of the nucleus (through the nuclear pore / nuclear membrane)
4. mRNA moves to a ribosome (in the cytoplasm)
5. The ribosome reads the base sequence of the mRNA and uses it to join amino acids in the correct order to make a protein / polypeptide

## Key terms

- [messenger RNA (mRNA)](https://www.gradenine.co.uk/glossary/messenger-rna-mrna)
- [template strand](https://www.gradenine.co.uk/glossary/template-strand)

## Related

- [Revision notes for Pearson Edexcel A-Level Biology A (9BI0)](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/a-scientist-compares-the-base-sequence-3049ebab) · Published by Druglandscape Ltd.