# Chromosomes are long, coiled molecules of DNA. DNA is a polymer made of two strands twisted around each other to form a double helix. Explain how the structure of DNA allows it to be replicated accurately during the cell cycle.

> Eduqas A-Level Biology — 1.5 Nucleic acids and DNA replication · Explain · 5 marks

> Before a eukaryotic cell can divide by mitosis, DNA replication must occur during interphase so that each daughter cell receives an identical copy of the genetic material.

## Mark scheme (5 marks)

1. DNA is made of two strands / is a double helix
2. The two strands of DNA unwind / separate / unzip
3. Each separated strand acts as a template for a new strand
4. Complementary base pairing ensures the new strand is identical to the original / bases pair in a specific way
5. Two identical DNA molecules are produced, each containing one original and one new strand

## Key terms

- [DNA](https://www.gradenine.co.uk/glossary/dna)
- [double helix](https://www.gradenine.co.uk/glossary/double-helix)
- [polymer](https://www.gradenine.co.uk/glossary/polymer)
- [chromosome](https://www.gradenine.co.uk/glossary/chromosome)
- [cell cycle](https://www.gradenine.co.uk/glossary/cell-cycle)

## Related

- [Revision notes for Eduqas A-Level Biology](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/chromosomes-are-long-coiled-molecules-of-f7f02397) · Published by Druglandscape Ltd.