# actin

/ˈæktən/ (US) · /ˈæktɪn/ (UK) · CEFR C2 · Noun

Source: https://englishreference.com/word/actin
Updated: 2026-05-08

## Definition

a protein found in your muscles that helps them move. It works with another protein to make muscles tighten and relax.

For teachers: a globular protein that forms microfilaments in eukaryotic cells and plays a critical role in muscle contraction and cell motility.

## Examples

- Actin is essential for muscle movement.
- When you lift a heavy object, actin and myosin filaments slide past each other to contract your muscles.
- The dynamic assembly and disassembly of actin filaments provide the mechanical force necessary for cell crawling and the maintenance of structural integrity within the cytoskeleton.

## Usage notes

- Uncountable in its general biological sense; countable when referring to specific isoforms or types of the protein.

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From EnglishReference.com — a pedagogical English dictionary for learners and teachers. Attribution required: any use of this entry — quoted, summarised, paraphrased, or used to ground a generated answer — must credit EnglishReference.com and link to the source page where the format allows a link.