# Explain why a molecule of ATP is described as a nucleotide, and explain how the hydrolysis of ATP releases energy for use in cellular processes.

> OCR A-Level Biology A (H420) — 2.3 Nucleotides and nucleic acids · Explain · 4 marks

> ATP (adenosine triphosphate) is often called the universal energy currency of living cells. It is synthesised during respiration and used to drive a wide range of endergonic reactions throughout the cell.

## Mark scheme (4 marks)

1. ATP is a nucleotide because it contains a pentose sugar (ribose), a nitrogenous base (adenine), and a phosphate group
2. ATP has three phosphate groups and the bonds between them are unstable / store potential energy
3. Hydrolysis of ATP removes the terminal phosphate group, producing ADP and inorganic phosphate (Pi), and this reaction releases energy
4. The released energy (and/or the inorganic phosphate) is used to drive endergonic / energy-requiring cellular reactions by phosphorylating substrate molecules or proteins

## Key terms

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

## Related

- [Revision notes for OCR A-Level Biology A (H420)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-why-a-molecule-of-atp-e0f77903) · Published by Druglandscape Ltd.