# Explain how the structure of a myosin head enables it to function as a molecular motor during skeletal muscle contraction.

> IB DP Biology Higher Level (2023 syllabus) — B3.3 Muscle and motility (HL only) · Explain · 4 marks

## Mark scheme (4 marks)

1. The myosin head contains an actin-binding site that allows it to attach to actin, forming a cross-bridge.
2. The myosin head has an ATPase active site that hydrolyses ATP to ADP and inorganic phosphate (Pi), providing the energy for the power stroke.
3. On hydrolysis of ATP, the myosin head pivots into a cocked (high-energy) conformation, ready to perform the power stroke.
4. Release of Pi triggers the power stroke: the myosin head changes conformation (rotates ~45°), pulling the actin filament towards the centre of the sarcomere, after which ADP is released.

## Key terms

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

## Related

- [Revision notes for IB DP Biology Higher Level (2023 syllabus)](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-how-the-structure-of-a-de0f9a38) · Published by Druglandscape Ltd.