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.


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

Please contribute to this project, if you have more information about this term feel free to edit this page

This page was last modified on 30 June 2009, at 12:00. This page has been accessed 21,379 times. 
What links here | Related changes | Permanent link