# Explain how a eukaryotic cell ensures that a polypeptide is only produced from the coding sequence of a gene, rather than from the entire pre-mRNA transcript.

> IB DP Biology Standard Level (2023 syllabus) — D1.2 Protein synthesis · Explain · 4 marks

## Mark scheme (4 marks)

1. Pre-mRNA contains non-coding intervening sequences called introns that must be removed before translation
2. The coding sequences (exons) are joined/ligated together after intron removal to form mature mRNA
3. This process of intron removal and exon joining is called RNA splicing / post-transcriptional processing
4. Only the mature mRNA (containing only exon sequences) is exported from the nucleus and used as a template for translation at ribosomes

## Key terms

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

## Related

- [Revision notes for IB DP Biology Standard Level (2023 syllabus)](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-a-eukaryotic-cell-ensures-0aedf7a4) · Published by Druglandscape Ltd.