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Describe at the mechanistic level how activated ras

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Unformatted text preview: at occur after an action potential travels down the T ­tubules of a muscle cell. You DO NOT have to describe the ATP binding and hydrolysis cycle of myosin II. (7 points) The voltage ­sensitive channel (dihydro ­pyridine or DHP receptor) opens (causing initial influx of calcium into the cytosol from the extracellular space) The (ryanodine) receptor on the ER (sarcoplasmic reticulum) membrane that is mechanically coupled to the DHP receptor opens, causing release of calcium from the ER into the cytosol (and increase in the concentration of calcium in the cytosol). Calcium binds (troponin C of) tropinin complex (on actin filaments), changing its conformation. This in turn displaces tropomyosin on actin filaments. (As a result, tropomyosin no longer binds to and blocks the myosin II ­binding site on actin filaments.) This allows Myosin II motor head (of thick filament) to bind and work on actin...
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