Ultra-Structure Of Myosin And Actin Filament

Myosin

It is thick in diameter, and consists of a tail which terminates in two globular head. Myosin tail consists of two long polypeptide chain coiled together. The heads are also called cross bridges as they link the thick and thin micro-filaments together during contraction.

Myosin and Actin Filaments

Actin

It is thin in diameter. The actin molecules are arranged in two chains which twist around each other. Twisting around the actin chains are two strands of another protein tropomyosin. The other major protein in the actin is troponin. It is actually three polypeptide complex, one binds to actin, another binds to tropomyosin while the third binds calcium ions.

Sliding Filaments

Z. Huxley and A. F. Huxley proposed 'sliding filament model, of muscle contraction. Impulses generated at a neuromuscular junction travel down a T- tubule to the calcium storage sacs, and calcium is released into the muscle fiber. Now the muscle fiber contracts as the sarcomeres within the myofibrils shorten. When a sarcomere shortens, the thin actin filaments slide past the thick myosin filaments and approach one another. This cause A band to shorten and the H zone to almost or completely disappear. The movement of actin filaments in relation to myosin filaments is called the sliding filament theory of muscle contraction. During the sliding process the sarcomere shortens even though the filaments themselves remain the same length. ATP supplies energy for muscle contraction. Although the actin filaments slide past the myosin filaments, it is the myosin filaments that do the work. Myosin filament break down ATP and have cross bridges that pull the actin filaments toward the center of the sarcomere.

The Sliding Filament Model

ATP supplies energy for muscle contraction. Although the actin filaments slide past the myosin filaments, it is the myosin filaments that do the work. Myosin filament break down ATP and have cross bridges that pull the actin filaments toward the center of the sarcomere.

Need of Respiratory Gas Exchange

Respiratory gas exchange is essential for most animals because it allows them to obtain the oxygen they need for cellular respiration, which is the process that generates energy in cells. During cellular respiration, glucose is broken down in the presence of oxygen to produce energy, carbon dioxide, and water.

In order to carry out this process, animals need to take in oxygen from their environment and release carbon dioxide. This is where respiratory gas exchange comes in. Through this process, animals exchange oxygen and carbon dioxide between their bodies and the environment.

In many animals, respiratory gas exchange occurs through specialized organs such as lungs or gills. In some smaller or simpler animals, gas exchange occurs directly across the body surface through a process called diffusion. Regardless of the specific mechanism, respiratory gas exchange is essential for animals to carry out cellular respiration and survive. Without sufficient oxygen, cells cannot generate the energy needed for basic life processes, and the accumulation of carbon dioxide can be toxic.