22). In the figure above which area(s) shorten(s) during muscle contraction? a.
ID: 210733 • Letter: 2
Question
22). In the figure above which area(s) shorten(s) during muscle contraction? a. c. I and IIl d. III and V e. all of them 23) What happens when Ca2 increases in the cytoplasm of a striated muscle cell? a. Myosin-binding sites on actin are exposed, allowing a single cross-bridge cycle to occur b. Myosin-binding sites on actin are exposed, allowing cross-bridge cycles to occur until Ca2 levels drop again. c. Actin-binding sites on myosin are exposed, allowing a single cross-bridge cycle to occur. d. Actin-binding sites on myosin are exposed, allowing cross-bridge cycles to occur until Ca2 drops again. 24) In striated muscle, phosphate is released from the myosin head and... a. the myosin head binds to actin. b. the myosin head releases from actin. c. the myosin head returns to the cocked position. d. the myosin head starts the power strokeExplanation / Answer
Answer 1: According to the given diagram;
I = Sarcomere, in which actin and myosin are organized into a linear chain of highly ordered structure.
II = M line,
III = Myosin
IV = Z disc
V = Actin
During muscle contraction the myosin sliding past the actin thin filament, with no change in the length of either type of the filamanet. So part I and III get shorten So, correct answer is (C).
Answer 2: As we know; Binding of calcium to troponin C, uncovering myosin binding sites on actin and formation of linkages between actin and myosin are two main steps of muscle contraction. So when calcium increased in the cytoplam of a straited muscle myosin-binding sites on actin are exposed, allowing cross- bridge cycles to occur until calcium levels drop again. So correct answer is (B).
Answer 3: In striated muscle, release of phosphate causes binding of the myosin head to a new site on the actin filament. This release triggers the power stroke ( the force generating change in shape during the head regains its original conformation). So the correct answer is option (d).
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