Dictionary > Tropomyosin


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

You will also like...

Homeostatic Mechanisms and Cellular Communication
Homeostatic Mechanisms and Cellular Communication

Homeostasis is the relatively stable conditions of the internal environment that result from compensatory regulatory res..

A chart depicting Mendel's Law of Dominance
Mendel’s Law & Mendelian Genetics

One of Mendel’s law of inheritance is the “law of dominance”. Read this tutorial to know more about this form of i..

"Cronopio dentiacutus", a prehistoric mammal (an illustration)
Mammalian Ancestors

Mammals are a diverse group of organisms, where most of them develop their offspring within the uterus of the mother. Ov..

Consciousness and behavior
Consciousness and Behavior

Human consciousness and behavior are an interesting topic since they are determined and controlled by the brain. Conscio..

Water in Plants

The movement of molecules (specifically, water and solutes) is vital to the understanding of plant processes. This tuto..

3D rendering of an antibody
Passive and Active Types of Immunity

Lymphocytes are a type of white blood cell capable of producing a specific immune response to unique antigens. In thi..