# Explain how the structure of a DNA nucleotide is related to its role in forming the polynucleotide strand.

> IB DP Biology Standard Level (2023 syllabus) — A1.2 Nucleic acids · Explain · 4 marks

## Mark scheme (4 marks)

1. A DNA nucleotide consists of a deoxyribose sugar, a phosphate group, and a nitrogenous base.
2. Covalent bonds (phosphodiester bonds) form between the phosphate group of one nucleotide and the deoxyribose sugar of the next, linking nucleotides together.
3. This produces a sugar–phosphate backbone that gives the polynucleotide strand its structural integrity/directionality (5' to 3').
4. The sequence of bases projecting from the backbone stores genetic information, because the specific order of bases encodes instructions (is not restricted by any structural rule).

## Key terms

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

## 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-how-the-structure-of-a-342a13fd) · Published by Druglandscape Ltd.