Question

5. For each of the following statements, decide whether it is True or False AND provide a justification for your decision A. The hydrolysis of ATP is required both for the contraction and relaxation of skeletal muscles. B. An actin filament will grow as long as actin monomers continue to be added to the plus end. C. In most animal cells, dyneins transport materials to the periphery of the cell, whereas kinesins transport material to the cell's interior.

Answer 1

(A)

ATP hydrolysis is required for both muscle contraction and relaxation. The myosin-actin cross-bridge breaks during muscle contraction by the ATP after being hydrolyzed by the ATPase activity.

During muscle relaxation, the angle of the myosin head is changed into a "cocked" position by the energy released during ATP hydrolysis.

Therefore, the statement is true.

(B)

Actin filaments have the ability to grow by the addition of the monomers to both the ends in a reversible manner but the plus end can elongate 5-10 times faster than the minus end because G-actin associates very easily to the plus end of the filament and it is harder for the G-actin to associate at the negative end.

Thus, the monomers can be added on both ends and the actin filament can grow from both ends.

Therefore, the statement is false.

(C)

Dyneins transport cargo from the periphery of the cell to the cell's interior or towards the center because they move towards the minus end of the microtubule.

Kinesins show anterograde transport because it transports cargo like membrane components and protein from the cell's interior towards the periphery of the cell as they walk towards the plus end of the microtubule.  

Therefore, the statement is false.