Biology, 02.07.2021 03:30, cadeduncan71

N Which statement best describes the step in muscle contraction when the sarcomere is the shortest?
A The sarcomere is contracted, and the actin and myosin filaments are partially overlapped.
B The sarcomere is relaxed, and the actin and myosin filaments are partially overlapped.
C The sarcomere is contracted, and the actin and myosin filaments are completely overlapped.
D The sarcomere is relaxed, and the actin and myosin filaments are completely overlapped.

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answered: caitlynnpatton1208

C The sarcomere is contracted, and the actin and myosin filaments are completely overlapped.

Explanation:

In rest, the tropomyosin inhibits the attraction strengths between myosin and actin filaments. Contraction initiates when an action potential depolarizes the inner portion of the muscle fiber. Calcium channels activate in the T tubules membrane, releasing calcium into the sarcolemma. At this point, tropomyosin is obstructing binding sites for myosin on the thin filament. When calcium binds to troponin C, troponin T alters the tropomyosin position by moving it and unblocking the binding sites. Myosin heads join the uncovered actin-binding points forming cross-bridges, and while doing so, ATP turns into ADP and inorganic phosphate, which is released. Myofilaments slide impulsed by chemical energy collected in myosin heads, producing a power stroke. The power stroke initiates when the myosin cross-bridge binds to actin. As they slide, ADP molecules are released. A new ATP links to myosin heads and breaks the bindings to the actin filament. Then ATP splits into ADP and phosphate, and the energy produced is accumulated in the myosin heads, which starts a new binding cycle to actin. Finally, Z-bands are pulled toward each other, shortening the sarcomere and the I-band, producing muscle fiber contraction.

In the sarcomere, which is the contractile unit of skeletal muscles, there are

Thick myosin myofilaments in the central region belonging to the A band. Thin filaments united to the Z lines, extending in the interior of the A band until they reach the border of the H band. Thin actin filaments composing the I band, which belong to two sarcomeres adjacent to a Z line.

When the muscle contracts, the muscular fiber gets shorter and thicker due to the reduction in the length of the sarcomere. The H line and the I band get shorter. The Z lines get closer to the A band, meaning that they get closer to each other. A band keeps constant in length. This change is produced by movement mechanisms that involve a change in the relative position of actin and myosin filaments.

answered: Guest

humans are now responsible for causing changes in the environment that hurt animals and plant species. we take up more space on earth for our homes and cities. we pollute habitats. human activity often changes or destroys the habitats that plants and animals need to survive.

answered: Guest

answer: i don't know

explanation:

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N Which statement best describes the step in muscle contraction when the sarcomere is the shortest?...