Question

You have a patient who has a very strange disorder. In this disorder, ADP sticks permanently to the myosin head. From your knowledge of excitation contraction coupling, describe how this patient will present. Defend your position. Please be clear, thank you!

Answer 1

Each myosin molecule contains a globular head and tail portion. The binding of ATP (adenosine triphosphate) to the head region of myosin hydrolyzes the ATP to ADP (adenosine diphosphate), releasing the phosphate bond; this hydrolysis provides the energy for muscle contraction. Then the thick myosin filaments slide over the thin stationary actin filaments and cross bridges are formed. The binding of ATP to the myosin head initiates the process of muscle contraction. The release of myosin head from the actin needs binding of another ATP molecule, otherwise, the muscle remains in the contracted state.

In the given case, the ADP sticks permanently to the myosin head, means ATP cannot bind and energy will not be available for muscle contraction. So, the patient presents the weakness in the muscle contraction and poor muscle strength. Difficulty in breathing, especially on physical activity.