Question

1.During skeletal muscle contraction, the following occurs except

A)ATP hydrolysis directly causes the movement of the myosin head to cause a power stroke

B)When the myosin head releases a phosphate, it can bind actin

C)When a new ATP binds to a myosin head, it releases actin

D)ATP hydrolysis activates the myosin head so it can bind actin

E)When the myosin head binding actin releases ADP, it moves to create the power stroke

2.During skeletal muscle contraction, the length of the actin and myosin filaments is reduced/shortened.
A)True

B)False

3.In a relaxed (non-contracting) skeletal muscle, there is a _________________ calcium concentration in the sarcoplasm than in the sarcoplasmic reticulum and transverse tubules.

A)higher

B)lower

C)the same

4.Elevated levels of myostatin can help our bodies to heal/repair damaged skeletal muscles.
A)True

B)False

Answer 1

Answer

(1)B

(2)B

(3)B

(4)A

Explanation:::

(1) During muscle contraction the role of Calcium ion and ATP is important.The thin filament actin and thick filament myosin makes a crossbridge during contraction. Normally troponin and tropomyosin occur in complex form so myosin head is not exposed for binding to actin.When calcium channel open due to action potential generation in neuromuscular junction, then it will enter the sarcoplasm,as the concentration of calcium increases it will bind to the troponin..then troponin tropomyosin Complex break as a result myosin head will exposed for binding with actin.

Myosin attracts actin and bind with them, to form crossbridge...during this step hydrolysis of ATP will occur which means ADP and Pi will present.During this step actin will remain bind with myosin as well as ADP and Pi...but after sometime Pi will release to make actin myosin bonding stronger...and moves towards the sarcomere make a powerstroke.During power stroke both ADP and Pi will release. And in the absence of high energy activation it will remain in crossbridge position.When new ATP will come it gives high energy which results into release of actin from myosin head and again ready for next contraction cycle.

Myosin normally have two binding site one for ACTIN and another for ATP...when actin binded with myosin ,it creates crossbridge and power stroke and when binded with ATP it detached from actin, for starting new contraction cycle.ATP hydrolysis promote actin myosin binding..

So,all the given options are correct regarding skeletal muscle contraction except option (B) because myosin head remain binded with actin as well as ADP and Pi...myosin release Pi after sometime for strong bonding with actin...it is not like that when Pi release then after only actin will bind ..

(2) The length of actin and myosin filament will not shorten during contraction because they only slides one over another.The size of sarcomere will be shorten during contraction because the I-band and H zone between them will shorten.The A-band remains the same....So actin myosin filament not reduce or shorten during contraction.

(3)As we know the concentration of calcium in muscle play major role in contraction and relaxation.If calcium level will high in sarcoplasm due to signal,it causes contraction.....after binding with troponin...and when calcium return to the Sarcoplasmic reticulum and T tubules the muscles will relax ....So in relaxation calcium is lower in sarcoplasm as compare to sarcoplasmic reticulum and T tubules.

(4) Myostatin is normally termed as negative regulator of muscle fibre which means when it is present in the muscles, it will decrease the functioning of muscle growth and when it is absent it cause increase in growth ,which sometimes forms tumor of muscle.So the main role of Myostatin to control extra growth or mass of muscles in the body.