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...

An artist depiction of a Precambrian multicellular life form.
The Evolution of Cell Organelles

The nucleus containing the genetic material, DNA, and the mitochondria, well-identified as the "powerhouse of the cell",..

Biosecurity and Biocontrol
Biosecurity and Biocontrol

This lesson explores the impact of biosecurity threats, and why they need to be identified and managed. Examples to incl..

Chromosomes X and Y and Sex Determination
Chromosomes X and Y and Sex Determination

This tutorial looks at sex determination via the sex chromosomes, X and Y. Read it to get more info on X and Y chromosom..

Evolution of Life - Ancient Earth
Evolution of Life – Ancient Earth

Autotrophs flourished, absorbing carbon and light. Soon after, primitive life forms that could assimilate oxygen thrived..

Carbohydrates, fats and proteins - dietary sources
A Balanced Diet – Carbohydrates and Fat

Apart from vitamins, the human body also requires high energy sources such as carbohydrates and fats. If you want an ove..

Early Mammals on Earth
Early Mammals on Earth

The Earth's ecosphere was rapidly changing and throwing up a wide range of ecological niches that new adaptive organisms..