You are studying myosin V, a class of myosin which can be used in cells to...

You are studying myosin V, a class of myosin which can be used in cells to transport vesicles by “walking” along actin filaments, towards the plus ends of these filaments. You have identified a mutation in the gene for myosin V that affects its ATP binding site. This mutant myosin V (M) can still perform the entire cross-bridge cycle, but it takes much longer to hydrolyze ATP compared to a wild type myosin V (W).

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

b) Would the duty cycle (the proportion of the cross-bridge cycle in which myosin is bound to actin) be longer in M or W?Explain?

c) How would this difference in duty cycle affect the ability of M to transport a vesicle along an actin filament? Explain.

Expert Solution

The duration of the cross bridge is greater or longer in M as compared to W. Head of the myosin linked or bind the actin and pulls the actin filaments towards inwards resulting in the contraction of muscles. This myosin has also the ATP hydrolysing property which helps to convert the ATP into ADP and organic phosphate with release of large amount of energy. This energy is used to detach the myosin from the actin and this results in the relaxation of the muscles . The mutant M has defective ATP binding site . Therefore , the hydrolysing of ATP does not takes place or it takes place at very slow rate . Therefore due to No or slow release of energy by the hydrolysis of ATP . The mutant M can still perform the entire cross bridge cycle phenomenon . But it occurs at a very slow rates results in the sluggish movement . Contraction of muscles takes place. Relaxation occurs only by release of energy that is released by the hydrolysis of ATP molecules. by the ATP binding site of the myosin. In the relaxed state of the muscles, the myosin and the actin are seperated. To seperate the myosin and actin from each other . Certain binding proteins binds to the myosin binding site on the actin . These proteins are known as Tropomyosin .
Hence , The cross bridge cycle will be longer in M .
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