What do Myosin and Actin do?
What is actin? What is myosin? Where are they found? What is their role in muscle contraction?
What is actin?
An actin molecule is a globular protein with binding site to which the myosin cross-bridges can attach, a
thin filaments, part of the contractile apparatus in muscle cells.
What is myosin?
Myosin is one of the two major proteins responsible for contraction of muscles. It is composed of two
twisted protein strands with projecting parts called cross-bridges. Many of these strands together form a
myosin filament. These globular portions of the myosin filaments contain an enzyme called ATPase,
which catalyzes the breakdown of ATP, releasing energy that puts the myosin cross-bridges in a cocked
position.
Where are they found?
Myosin and actin are found in myofibrils, which are found in the muscle fibers.
What is their role in muscle contraction?
The sliding filament theory of muscle contraction states that the head of myosin cross-bridges can attach
to an actin binding site and bend slightly, pulling the actin filaments with it. So myosin and actin help
muscle to produce movement.
What happens during contraction of a myofibril and how myosin and actin work?
http://www.blackwellpublishing.com/matthews/myosin.html
Myosin and actin are found in the myofibrils in the muscle. The myosin and actin work together to make
the muscle contract. Myosin has protein heads on the filament that reach out and attach to the actin’s
places of attachment. The tropomyosin covers the places of attachment when the muscle isn’t contacting.
Here is the link to a great animated video explaining the roles of actin and myosin in muscle contraction.
There is also a little quiz at the end to test your understanding.Animation: Myofilament Contraction
The Role of Troponin and Tropomyosin:
What is Troponin?
Troponin is made up of three proteins that are essential for muscle contraction for skeletal and cardiac
muscles.
What is Tropomyosin?
Tropomyosin is an actin-binding protein. It acts to regulate how myosin crossbridges attach to actin
filaments. Tropomyosin work with with the troponin complex and together associate with actin in muscle
fibers to regulate muscle contraction by regulating the binding of myosin.
The Role of Acetylcholine in Muscle Contraction
Acetylcholine is a neurotransmitter -- a chemical in the brain that helps transmit electrical impulses
generated by nerves. Acetylcholine plays a vital role in the peripheral nervous system by activating
muscle cells. It also plays a role in the central nervous system by enhancing sensory perceptions and
increasing attention. Substances that block acetylcholine in the muscles inhibit muscle contraction and
function.