3. You are studying myosin IIb, and you have identified a mutation in the gene f

Question

3. You are studying myosin IIb, and you have identified a mutation in the gene for myosin IIb that affects its ATP binding site. This mutant myosin IIb (M) can still perform the entire cross-bridge cycle, but it takes much longer to hydrolyze ATP compared to a wild type myosin II (W).

a) Would the duration of the cross-bridge cycle be longer in M or W? Explain.

b) How would the rate of contraction of the mutated muscle fiber be affected? Explain.

4. The condition myasthenia gravis is caused by circulating antibodies that bind to and inactivate the nicotinic ACh receptor.

What would you predict would be the effect of the advanced stages of this condition on muscle contraction? Explain. (Assume all the nicotinic ACh receptor are affected)

Explanation / Answer

3.(a)

The duration of cross-bridge cycle would be longer in case of M because it will take additional time for the mutant myosin IIb(M) to hydrolyze ATP so the time taken for the entire cross-bridge cycle would be more for M compared to W.

3.(b) The rate of contraction of mutated muscle will be lesser compared to wild type myosin because the time taken for cross-bridge will be more for mutated muscle so for equal concentration of both gene the time taken in M is more so the rate of mutated muscle will be less compared to original muscle.

4.

If the nicotinic ACh receptor is inactivated by antibodies then the muscle contraction will be affected because all the antibodies will bind to Ach receptors so there will be lesser contraction of muscles because these receptors are affected so the contraction is decreased so that it does not perform any action because of the antibodies binding to the receptors

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