# Describe the structure of a DNA nucleotide and explain how nucleotides are joined together to form a single strand of DNA.

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

## Mark scheme (5 marks)

1. A DNA nucleotide is made up of a deoxyribose (sugar) molecule
2. A DNA nucleotide contains a phosphate group
3. A DNA nucleotide contains one of four bases (adenine, thymine, cytosine or guanine)
4. Nucleotides are joined by condensation reactions / covalent bonds form between the sugar of one nucleotide and the phosphate of the next
5. This forms a sugar-phosphate backbone along the length of the strand

## Key terms

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

## Related

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Source: [GradeNine](https://www.gradenine.co.uk/q/describe-the-structure-of-a-dna-e01f77ee) · Published by Druglandscape Ltd.