A look inside the muscle machinery
Let's lift the hood and take a look at the machinery. Muscle cells are made up of many long, tiny fibers composed chiefly of a protein called myosin. These fibers are chock full of ATP. In the early 1950's Albert von Szent Gyorgyi, a Hungarian born biochemist, (who had come to the United States,) brought about muscular contraction in a test tube. In 1937 he received the Nobel Prize in Medicine for his earlier work. He managed to cause the myosin threads of muscle to lose all of their ATP. He then added to these lengthened threads, some ATP. The long threads curled up instantly on contact with the source of energy. Contraction of the myosin threads is the mechanism for contraction of a muscle. This demonstration is a milestone in the history of science, for in Szent-Gyorgyi's words:

"Motion is one of the most basic biological phenomena and has always been looked upon as the index of life. Now we could produce it in a test tube with constituents of the cell."

The contraction of muscle threads lacking ATP explains the hitherto puzzling stiffness (rigor mortis) which sets in soon after an animal cell dies. The ATP present in the muscle is slowly decomposed after death, and, since the enzymes that break down sugar are forever stalled, the ATP is never built up again. Without ATP, the muscle fibers shorten and cause the corpse to become rigid.

ATP has also been shown recently to be the source of energy for the light which some organisms are able to produce (like fireflies). It is also the source of electrical energy in nerve tissues and in the electric organs of animals which can accumulate and discharge electricity (like the electric eel). Thus, ATP can be tapped to supply all the forms of energy a living organism can generate: heat and light, and mechanical, electrical, and chemical energy.

The End

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