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

One color shows the cell nucleus (to mark where each cell is) and others show the structural component actin (which determines the shape of the cell) and the microtubules that are part of the communication and transport network within a cell. —Eva Amsen, Forbes, 17 Oct. 2024

Dormant NSCs in Drosophila have a protrusion that extends from the cell body; the researchers had recently demonstrated that the protrusion is enriched with actin microfilaments. —New Atlas, 15 Aug. 2024

The arrangement of actin within cells is regulated by another type of protein called formin, which accelerates the assembly of a particular actin, filamentous actin (f-actin). —New Atlas, 15 Aug. 2024

Rome proposes that vaults might be ferrying the blueprint for actin to the construction sites. —Betsy Hanson, Discover Magazine, 11 Nov. 2019

One place where vaults seem to clump together is where the cell is building long fibers of the protein actin that make up part of the cell’s internal skeleton. —Betsy Hanson, Discover Magazine, 11 Nov. 2019

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

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