The Contro of Biochemic Rextion
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چکیده
T g anism and a machine holds true to a remarkable extent at all levels at which it is investigated. To be sure, living things are machines with exceptional powers, set apart from other machi~les by their ability to adapt to the environment and to reproduce themselves. Yet in all their functions they seem to obey mechanistic laws. An organism can be compared to an automatic factory. Its various structures work in unison, not independently; they respond quantitatively to given commands or stimuli; the system regulates itself by means of automatic controls consisting of specific feedback circuits. These principles have long been recognized in the behavior of living organisms at the physiological level. In response to the tissues' nccd for niore oxygen during exercise the heart speeds up its pumping of blood; in response to a rise in the blood-sugar level the pancreas increases its secretion of insulin. Now analogous systems have been discovered at work within the living cell. The new finding4 of molecular biology show that the cell is a mechanical microcosni: a chemicc~l machine in which the various structures are interdependent and cont~olled by feedbaclc systems quite similar to the systems devised by engineers who specialize in control theory. In this article we shall survey the experimental findings and hypotheses that have developed from the viewpoint that the cell is a selfregulating machine. We can think of the cell as a completely automatic chenlical factory designed to make the most economical use of the energy available to it. It manufactures certain products-for example proteins-by means of series of reactions that constitute its production hy Jcan-Pierre Chailgcux
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