# Explain why DNA is described as a polymer, and describe how the two strands of a DNA molecule are held together.

> AQA A-Level Biology (7402) — 3.1.5 Nucleic Acids · Explain and Describe · 5 marks

## Mark scheme (5 marks)

1. DNA is a polymer because it is made of many repeating units / monomers joined together
2. The monomers / repeating units of DNA are nucleotides
3. The two strands are held together by bonds / base pairing between the bases
4. The base pairing is complementary / specific — A pairs with T, and C pairs with G
5. The two strands run in opposite directions / are antiparallel, forming a double helix

## Key terms

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

## Related

- [Revision notes for AQA A-Level Biology (7402)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain and Describe" 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-why-dna-is-described-as-f82a0a20) · Published by Druglandscape Ltd.