# Explain how the structure of a DNA nucleotide is related to its role as a monomer in the formation of a 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 one of four nitrogenous bases.
2. Adjacent nucleotides are joined by covalent (phosphodiester) bonds formed between the phosphate group of one nucleotide and the deoxyribose sugar of the next.
3. This repeated sugar–phosphate linkage forms the sugar–phosphate backbone of the polynucleotide strand.
4. The nitrogenous base of each nucleotide projects inward (away from the backbone) and is available for complementary base pairing, which allows the strand to carry and transmit genetic information.

## 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-d950d9a5) · Published by Druglandscape Ltd.