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Actin

Recommended video: Cells and tissues [24:29]
Overview of the main cellular components and tissues.

Actin filaments (polymerized from actin monomers) form the major protein constituent of the cytoskeleton of eukaryotic cells (for which they are known as microfilaments) and play a pivotal role in muscle contraction and cell movement. They form thin, flexible fibers and are approximately 7 nm in diameter. 

Actin exists in two forms: G-actin (monomeric globular actin) and F-actin (polymeric fibrous actin). G-actin is responsible for the formation of the actin filament, while F-actin forms the cytoskeleton and contractile apparatus of muscle cells.

Actin filaments organize into bundles or dynamic networks which play fundamental roles throughout different cellular processes. Actin bundles are cross-linked and closely packed into parallel arrays, while in actin networks, actin filaments are loosely cross-linked and form three-dimensional mesh works.

The main functions of actin filaments include:

  • Forming a dynamic cytoskeleton to provide structural support to cells.
  • Supporting and allowing cell motility.
  • Supporting muscle contractions as actin filaments slide alongside myosin filaments. In muscle, actin molecules twist together to form a 'thin filament' which interdigitate with thick filament bundles of myosin (muscle protein). Together actin and myosin filaments are known as myofilaments. 
Terminology English: Actin
Latin: Filamentum actini
Definition Major protein constituent of the cytoskeleton of eukaryotic cells
Function Form dynamic cytoskeleton, provide structural support to cells, allow cell motility, support muscle contractions 

Take a closer look at the cells and tissues of the human body in the study unit below: 

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