How Actin and Myosin Interact With Each Other to Shorten a Sarcomere
Your muscles work in a similar fashion. Muscles are composed of two major protein filaments: a thick filament composed of the protein myosin and a thin filament composed of the protein actin. Muscle contraction occurs when these filaments slide over one another in a series of repetitive events. Let's see how myosin molecules play a role similar to the oars of a rower.
sarcomere is end to end A given myofibril contains approximately 10,000 sarcomeres, each of which is about 3 micrometers in length. While each sarcomere is small, several sarcomeres added together span the length of the muscle fiber. Each sarcomere consists of thick and thin bundles of proteins referred to as myofilaments. If we magnify a portion of the myofilaments, we can identify the molecules that compose them. Thick filaments contain myosin, while thin filaments contain actin. Actin and myosin collectively are referred to as the contractile proteins, which cause muscle shortening when they interact with each other. Additionally, thin filaments contain the regulatory proteins troponin and tropomyosin, which regulate interaction between the contractile proteins. The I band is that part of the sarcomere that contains thin filaments, while the A band contains an area of overlap between the thin and the thick filaments. As you can see, a single I band spans two neighboring sarcomeres. A Z line attaches those neighboring sarcomeres. The thin filaments are attached to the Z lines on each end of the sarcomere, while the thick filaments reside in the middle of the sarcomere.
A picture emerges of the main molecular steps involved in the force-producing process; steps that are also likely to be seen in non-muscle myosin interactions with cellular actin filaments. Finally, the remarkable advances made in studying the effects of mutations in the contractile assembly in causing specific muscle diseases, particularly those in heart muscle, are outlined and discussed.In human bodies and those of other animals there are beautifully designed molecular mechanisms which move our limbs, or pump our blood, or aid in peristalsis, and there are motile mechanisms in all cells that move cell organelles or other cargoes from one part of the cell to another (Gautel M., 2016). In all cases, molecules which are enzymes that can utilise the energy stored in adenosine triphosphate (ATP) move along molecular tracks.
The process appears to require the development of tension between the front and rear of the cell, generating contractile force that eventually pulls the rear of the cell forward. This aspect of cell locomotion is impaired in mutants of Dictyostelium lacking myosin II, consistent with a role for myosin II in contracting the actin cortex and generating the force required for retraction of the trailing edge.
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