Question

During muscle contraction:
A. ATP is broken down
B. ATP is formed
C. GTP is broken down
D. None of the above

Answer 1

Hint: Two muscles work together to cause the movement. Muscles cause locomotion as they have properties such as excitability, elasticity, contraction and relaxation. Each muscle contains muscle fibres which inturn has alternative dark and light filaments called myosin and actin respectively. The muscle contraction is caused when the thin filament (actin) slides over the thick filament (myosin).

Complete Step by Step Answer:
The motor neurons bring the signals to the sarcolemma and release the neurotransmitter into the neuromuscular junction and generate an action potential. This action potential spreads through the whole of the muscle fibre and stimulates the release of calcium ions. These calcium ions bind with the troponin on the actin filaments and remove the masking of the active site for the myosin. Now, the actin and myosin filaments bind together to form a cross bridge using ATP hydrolysis (breakdown in the presence of water). This formation of a crossbridge results in the shortening of H-zone and I-band, thus in the muscular contraction.

Thus, the correct answer is option A:- ATP is broken down.

Note: After contraction myosin releases ADP and P1 and goes back to its relaxed state. The new binding of ATP takes place and the crossbridge is broken. The myosin head again hydrolyse the ATP and the cycle of cross bridge formation and breakage is repeated that causes further sliding and another contraction.
Red fibres are the muscles that have high myoglobin content which gives them their red colour. These red fibres also have plenty of mitochondria which can utilize large amounts of oxygen that is stored in them for ATP production.