Muscle contraction myosin-based

The contraction of muscles from all sources occurs by the general mechanism described above. Muscles from different organisms and from different cells and tissues within the same organism may have different molecular mechanisms responsible for the regulation of their contraction and relaxation. In all systems, plays a key regulatory role. There are two general mechanisms of regulation of muscle contraction actin-based and myosin-based. The former operates in skeletal and cardiac muscle, the latter in smooth muscle. 

The musculature is what makes movements possible. In addition to the skeletal muscles, which can be contracted voluntarily, there are also the autonomically activated heart muscle and smooth muscle, which is also involuntary. In all types of muscle, contraction is based on an interplay between the proteins actin and myosin. 

Calcium is known to be an important key regulator for contractile activities of both skeletal and smooth muscles. There are two general mechanisms of regulation of muscle contraction actin based and myosin based. 

Smooth muscles have molecular structures similar to those in striated muscle, but the sarcomeres are not aligned so as to generate the striated appearance. Smooth muscles contain a-actinin and tropomyosin molecules, as do skeletal muscles. They do not have the troponin system, and the fight chains of smooth muscle myosin molecules differ from those of striated muscle myosin. Regulation of smooth muscle contraction is myosin-based, unlike striated muscle, which is actin-based. However, like striated muscle, smooth muscle contraction is regulated by Ca. ... 

Microfilaments of F actin traverse the microvilli in ordered bundles. The microfila-ments are attached to each other by actin-as-sociated proteins, particularly fimbrin and vil-lin. Calmodulin and a myosin-like ATPase connect the microfilaments laterally to the plasma membrane. Fodrin, another microfila-ment-associated protein, anchors the actin fibers to each other at the base, as well as attaching them to the cytoplasmic membrane and to a network of intermediate filaments. In this example, the microfilaments have a mainly static function. In other cases, actin is also involved in dynamic processes. These include muscle contraction (see p. 332), cell movement, phagocytosis by immune cells, the formation of microspikes and lamellipo-dia (cellular extensions), and the acrosomal process during the fusion of sperm with the egg cell. 

Oshima, K., Takezawa, Y., Sugimoto, Y., Kiyotoshi, M., and Wakabayashi, K. (2003). Modeling analysis of myosin-based meridional X-ray reflections from frog skeletal muscles in relaxed and contracting states. Adv. Exp. Med. Biol. 538, 243-249. 

In terms of the molecular process whereby ATP forms and functions as biology s energy coin, there are two aspects—the protonation/ deprotonation of carboxylates due to a proton concentration gradient that drives a rotor to form ATP from ADP and Pi, as in the ATP synthase, and the molecular process whereby the breakdown of ATP to ADP with release of Pj drives the protein-based machines of biology, as in the myosin II motor of muscle contraction. 

The above three discussed protein-based machines—Complex III of the electron transport chain, ATP synthase/Fj-ATPase, and the myosin II motor of muscle contraction—represent the three major classes of energy conversion that sustain Life. Therefore, the facility with which the consilient mechanisms explain their function indeed support the thesis that biology s vital force arises from the coupled hydrophobic and elastic consilient mechanisms. 

Figure 4.4. Model of muscle contraction based on sliding filaments [ 2 ] (a) The bands H and I are shortened during contraction the length of thick and thin filaments remain constant the arrows indicate the myosin and actin-G polarity (b) Schematic representation of the interactions between myosin head and thin filaments during contraction.

---