actin

1 of 2

noun

ac·​tin ˈak-tən 

: a cellular protein found especially in microfilaments (such as those comprising myofibrils) and active in muscular contraction, cellular movement, and maintenance of cell shape

actin-

2 of 2

combining form

variants or actini- or actino-

1

: having a radiate form

actinolite

2

: actinic radiation (such as X-rays)

actinometer

Examples of actin in a Sentence

Recent Examples on the Web

Noun

Structural basis of actin sequestration by thymosin-beta4: implications for WH2 proteins. —The Salt Lake Tribune, 16 Aug. 2023

The cells produce specific proteins—actin and myosin—that cause muscles to contract and relax like rubber bands at different speeds. —Lauren J. Young, Scientific American, 2 July 2023

Her team had not only isolated and cultivated the organism for the first time but shown that its flailing filaments were made of actin, the protein that forms a skeletal scaffold in almost all complex cells, or eukaryotes. —Joshua Sokol, Quanta Magazine, 11 Apr. 2023

By amassing actin at their point of entry, Neisseria actually stimulates the cell to produce a barricade that prevents them from breaking through. —Ed Yong, Discover Magazine, 25 Aug. 2010

Other microorganisms travel using amoeboid movement, driven by flexing of their cellular skeletons, built from the protein actin. —Tom Siegfried, Smithsonian, 26 Sep. 2019

Filaments of the protein actin, for example, could have stabilized contacts between the hosts and symbionts and improved the coupling of their metabolisms. —Quanta Magazine, 9 Apr. 2019

Wan believes the cell’s preference depends on the interplay between two elements of the cellular skeleton: actin and myosin. —Tim Vernimmen, Quanta Magazine, 31 Jan. 2017

Nearly all multicellular animals, except for simple ones like sponges, depend on muscles to move, and all their muscles use some form of contracting fibers in which filaments of the proteins actin and myosin pull past one another to generate force. —Quanta Magazine, 13 June 2018

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Word History

Etymology

Noun

probably from act entry 2 or act(ivate) + -in entry 1

Combining form

borrowed from Greek aktino-, from aktīn-, aktís "ray, beam, spoke of a wheel"

Note: The Greek word has traditionally been linked with Sanskrit aktú-, conjectured to mean "twilight," and with Germanic *uŋhtwōn- "last part of the night, dawn," whence Old English ūhte "twilight, daybreak," Old High German uohta "dawn," Old Norse ōtta "last part of the night," Gothic uhtwo "dawn," from Indo-European *n̥k^wt-u-n-, a zero-grade derivative of *nok^wt-/*nek^wt- "night" (see night entry 1). Robert Beekes (Etymological Dictionary of Greek, Leiden, 2009) rejects this connection on the grounds that aktís "shows no trace of a labiovelar." In reference to actinic radiation, the formative actino- was probably first used by John herschel in actinometer (1833).

First Known Use

Noun

1942, in the meaning defined above

Kids Definition

actin

noun

ac·​tin ˈak-tən 

: a protein of muscle that with myosin is active in muscular contraction

Medical Definition

actin

noun

ac·​tin ˈak-tən 

: a protein found especially in microfilaments (as those comprising myofibrils) and active in muscular contraction, cellular movement, and maintenance of cell shape see f-actin, g-actin