Tropomyosin

Definition

noun

A long protein strand composed of two fully alpha helical chains in a coiled-coil dimmer, and binds along the length of the actin filament. It is also bound to bead-like protein complex (troponin) in which, together, they regulate the actin-myosin interations in muscle contraction.


Supplement

The tropomyosin, together with troponin, acts like a "molecular switch" that controls the interaction of actin and myosin.

In the absence of a nerve impulse, the tropomyosin lies fittingly on the groove of the actin filament, blocking the myosin-binding sites in actin. At this point the muscle is said to be relaxed or at rest. In the presence of nerve impulse, a cascade of reactions occurs that causes the release of calcium ions (from the sarcoplasmic reticulum). The calcium then binds to troponin, which causes a shift in the position of tropomyosin-troponin on the actin filament, unblocking the myosin-binding sites. This allows the myosin heads to bind with actin molecules, resulting in muscle shortening and contraction. Soon, the calcium levels become low again that the troponin-tropomyosin shifts back, blocking the myosin-binding sites again.


See also: troponin, actin filament

Retrieved from "http://www.biology-online.org/bodict/index.php?title=Tropomyosin&oldid=96461"
First | Previous (Tropism) | Next (Troponin) | Last
Please contribute to this project, if you have more information about this term feel free to edit this page.