# Explain the roles of helicase and DNA polymerase during DNA replication.

> IB DP Biology Standard Level (2023 syllabus) — D1.1 DNA replication · Explain · 4 marks

## Mark scheme (4 marks)

1. Helicase unwinds / uncoils the double helix
2. Helicase breaks the hydrogen bonds between complementary bases, separating the two strands
3. DNA polymerase adds free nucleotides to the 3′ end of the growing strand, forming new complementary strands
4. DNA polymerase uses each original strand as a template, joining nucleotides via phosphodiester bonds to produce two identical DNA molecules

## Key terms

- [helicase](https://www.gradenine.co.uk/glossary/helicase)
- [DNA polymerase](https://www.gradenine.co.uk/glossary/dna-polymerase)

## 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-the-roles-of-helicase-and-7f01ee45) · Published by Druglandscape Ltd.