When you hold a weight at arm's length, you are not doing any thermodynamic work but the muscles supporting the weight are nevertheless consuming energy.  Describe, on the molecular level, how muscles might maintain such state of constant tension without contracting. Why does this state consume ATP?

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Asked Nov 13, 2019
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When you hold a weight at arm's length, you are not doing any thermodynamic work but the muscles supporting the weight are nevertheless consuming energy.  Describe, on the molecular level, how muscles might maintain such state of constant tension without contracting. Why does this state consume ATP?

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Expert Answer

Step 1

Muscle contraction:

It is defined as the activation of tension-producing locations within muscle fibers.

In physiology it does not usually mean the shortening of muscle. The reason is that the production of muscle tension can occur without the modifications in the muscle length. This includes the holding of a dumbbell or a heavy book at the same position. The muscle relaxation takes place at the end of the muscle contraction.

Muscle relaxation is the returning of the muscle fibers to their initial low tension-producing state.

Step 2

Normally , the muscle contraction cycle at molecular level is given below:

  1. The active site located on the actin molecule is exposed to the calcium ions that binds to the troponin.
  2. The myosin head then makes a cross-bridge with actin.
  3. During the power stroke, the myosin head bends, and ADP and phosphate are released.
  4. A new ATP molecule get attach to the myosin head and breaks the myosin-actin cross bridge.
  5. ATP hydrolyzes to ADP and inorganic phosphate. This returns the myosin to cocked position.
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Troponin Ca Tropomyosin DOON Active site Myosin head- ADP Actin ATP ATP and Musele Contraction at molecalar level

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Step 3

Normlly, ATP facilitates the muscle Contraction:

  1. ATP is necessary for the contraction muscle because it disrupts the cross-bridge between the myosin and actin. It makes the myosin free to take part in the next muscle contraction.
  2. ATP makes the myosin capable for binding with actin by providing it a “cocked” position and higher- energy state.
  3. Once a cro...

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