# Explain how the sequence of nucleotides in a gene is used to determine the sequence of amino acids in a polypeptide, referring to both transcription and translation.

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

## Mark scheme (4 marks)

1. During transcription, RNA polymerase reads the template strand of DNA and synthesises a complementary mRNA strand using base pairing (A–U, T–A, G–C).
2. Each non-overlapping triplet of three consecutive nucleotides on the mRNA is a codon that corresponds to a specific amino acid (or start/stop signal) according to the genetic code.
3. During translation, tRNA molecules with a specific anticodon carry a specific amino acid and undergo complementary base pairing with the matching codon on the mRNA at the ribosome.
4. Peptide bonds form between successive amino acids as the ribosome moves along the mRNA, producing a polypeptide whose primary sequence is dictated by the original gene sequence.

## Key terms

- [transcription](https://www.gradenine.co.uk/glossary/transcription)
- [translation](https://www.gradenine.co.uk/glossary/translation)

## Related

- [Revision notes for IB DP Biology Higher 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-the-sequence-of-nucleotides-b6236a43) · Published by Druglandscape Ltd.