We may now ask: If living organisms are composed of molecules that are intrinsically inanimate, why does living matter differ so radically from nonliving matter, which also consists Of intrinsically inanimate molecules? Why does the living organism appear to be more than the sum of its inanimate parts? Early philosophers would have answered that living organisms are endowed with a mysterious and divine life force. But this doctrine, called vitalism, is nothing more than superstition, and it has been rejected by modern science.
Today, the central goal of the science of biochemistry is to determine how the collection of inanimate molecules found in living organisms interact with each other to constitute, maintain, and perpetuate the living state.
Biochemistry is a very young science. Until the last few decades, only a very few universities recognized it as a science in its own right. There are two parent lines in the genealogy of present-day biochemistry. One line arose from medicine and psychology, a by-product of early inquiries into the chemical composition of blood, urine, and tissue and their variation in health and disease. The other lineage traces from Organic chemistry, from early studies of the structure of naturally occurring organic compounds. For a long time, biochemistry was simply regarded as a branch of Psychology or as a branch of chemistry. It did not really emerge as a Full-fledged in its own rights, with powerful experimental method and predictive insight into biological phenomena, until the last quarter-century. Two major developments brought this about. One was the recognition of multienzyme systems as catalytic units in the major metabolic pathways and the development of a unifying hypothesis for the transfer of energy of the living cell. The other which has had a most pervasive and profound influence was the recognition that heredity, one of the most fundamental aspects of biology – the differentiation of cells and the organism, the origin of life and evolution, behavior and memory, and human diseases -probes which have demonstrated that this basic problem can be fruitfully approached by the biochemical method.
Indeed, the success of biochemistry in explaining many cellular phenomena has been so great that many scientists have come to the conclusion that biology is chemistry. Some biologists do not share this view; they maintain that the essence or gestalt of complex living organisms cannot be reduced, now or ever, to the level of molecules and molecular interaction. But this is the minority view. Today it is a perhaps more logical assumption, as a working philosophy, that all biological phenomena are ultimate molecular in basis and to abandon this view only when it is no longer useful for designing critical experiments or for explaining experimental data.
We must not, however, look upon biology as merely another branch of classical chemistry, such as organic chemistry, physical chemistry, or inorganic chemistry. If biology is chemistry, it must be a kind of Super chemistry that includes but at the same time transcends classical chemistry. This is because molecules found in a living organism not only conform to all the familiar physical and chemical principles governing the behavior of all molecules but, in addition, interact with each other in accordance with another set of principles that we shall refer to as the molecular logic of the living state. These principles do not necessarily involve any new or yet undiscovered physical laws or forces. Rather, they should be regarded as a set of ground rules that govern the nature, function, and interactions of the specific types of molecules found in the living organism, that endow them with the capacity for self-organization and self-replication. Not all the principles comprised by the molecular logic of the living state have yet been identified; Indeed, some are only dimly perceived. In fact, it is perhaps more appropriate to speak of the principle as axioms, since some of them are intuitive and not provable.
Now let us see if we can identify some important axioms in the molecular logic of the living state. We shall begin with a brief survey of the structure and function of the molecules found in the living matter, which we shall henceforth call Biomolecules.
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