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

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

## Mark scheme (4 marks)

1. The base sequence of DNA is transcribed into a complementary mRNA sequence (by RNA polymerase), producing a pre-mRNA / mRNA strand.
2. Each group of three consecutive bases on mRNA forms a codon, and each codon specifies a particular amino acid.
3. During translation, tRNA molecules with complementary anticodons carry specific amino acids to the ribosome and base-pair with the codons on mRNA.
4. Amino acids are joined by peptide bonds in the order dictated by the mRNA sequence, so the linear sequence of codons determines the primary structure (sequence of amino acids) of the polypeptide.

## 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)

---
Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-the-sequence-of-bases-baf2b9af) · Published by Druglandscape Ltd.