As mentioned in class, one additional major use of ATP in skeletal muscle (besides powering the myosin heads) is the recycling of calcium ions back into the sarcoplasmic reticulum after depolarization. The resting concentration of Ca++ in the muscle cell cytoplasm is about 50-100 nM, and the spike concentration after depolarization is about 10-20 μΜ. a) Consider a single sarcomere. What is the number of free calcium ions within the sarcomere at rest? What is the number of free calcium ions after depolarization? b) The major ion pump responsible for calcium ion recycling is SERCA (sarco/endoplasmic reticulum calcium ATPase). SERCA uses one molecule of ATP to pump two calcium ions, and the resting level can be restored in about 10-20 ms. How many molecules of ATP are used in a single sarcomere for pumping calcium in a single "twitch"? c) Assume that a single "twitch" is sufficient to drive one sarcomere from its fully extended length (about 2.5 µm) to its fully contracted length (about 1 µm). How many ATPs are used to power myosin contraction? How does this compare to the number of ATPs used for calcium recycling? (Be sure to state your assumptions explicitly.)

Q: requires

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Muscle Action

A change in the body or a bodily organ as a result of its functioning is referred to as an action. Muscle action can be defined as the specific movement of a bodily part generated by the contraction of a muscle. The muscle proteins actin and myosin are the important contractile proteins involved in muscle action. Muscle contraction, in addition to movement, serves several other important functions in the body, including posture, heat generation, and joint stability. Muscle contraction maintains posture, which includes standing and sitting.