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LIFE 210 (38)

Muscle, sarcomere, contraction, cell crawling

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Life Science
LIFE 210
Paul Laybourn

16 November Types of muscle Skeletal muscle Cardiac muscle and smooth muscle Muscle contraction depends on the ATP-driven sliding of highly organized arrays of actin filaments against myosin II filaments. Skeletal muscle cells, also called muscle fibers A muscle fiber is a huge single cell formed during development by the fusion of many separate myoblasts. Typically 50 μm in diameter and up to several centimeters long Contains the myofibrils A myofibril consists of a long repeated chain of sarcomeres The sarcomere is the contractile unit. Partly overlapping array of parallel thin (actin) and thick (Myo II) filaments Electron micrograph of an insect flight muscle viewed in cross section Region of overlap between thin and thick filaments. Hexagonal lattice. The ~300 myosin heads in a thick filament are not coordinated, therefore low processivity is critical. Organization of accessory proteins in a sarcomere Actin filament plus end binds to the Z disc, which is built by CapZ and α-actinin Nebulin is a large protein with an actin-binding repeat. Molecular ruler Tropomodulin positions the thick filament midway between the Z discs. Molecular spring The force generated during contraction depends on the degree of overlap of the thick and thin filaments. Muscle contraction is triggered by a nerve impulse that results in release of acetylcholine at the neuromuscular junction (synapse). 2+ A sudden rise in cytosolic [Ca ] initiates muscle contraction. Ca enters the cell and triggers more Ca release from the sarcoplasmic reticulum that
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