Collections:Texts:Chemistry:Chapter 20 - Molecules In Living Systems
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MOLECULES IN LIVING SYSTEMS
20.2 The Building Blocks of Biochemistry
Most of us have little difficulty distinguishing living organisms from inanimate matter. The former are capable of reproducing nearly exact copies of themselves; they can appropriate both matter and energy from their surroundings, moving, growing, and repairing damage caused by external factors; and groups of them evolve and adapt in response to long-term environmental changes. On a macroscopic scale the differences are sufficiently striking that early philosophers and scientists postulated the existence of a vital force without which living organisms would be inanimate. It was thought that organic compounds could only be manufactured in living organisms, and chemistry was divided into the subfields of inorganic and organic on this basis.
This subdivision persists today, but the definition of organic has changed in response to the discovery of numerous ways to make organic compounds from inorganic starting materials. As we saw in Chap. 8, organic chemistry now means “chemistry of compounds containing carbon.” No restriction is placed on the origin of the compounds, and hundreds of thousands of organic compounds which are foreign to all living systems have been produced in laboratories around the world. Indeed, concern about the effects of some of these synthetic substances on the environment has led to yet another definition of organic. The general public now takes it to mean “free of substances produced as a result of human activities.”
Just as the division between organic and inorganic chemistry has become more arbitrary with the advance of knowledge, the distinction
between life and nonlife has also blurred. Living organisms are made up of atoms and molecules which follow the same chemical principles that we have already discussed in this book. Yet there is a difference-these atoms, molecules, and even groups of molecules are organized to a much greater degree than in any of the cases we have discussed so far. Above a certain level of complexity a collection of chemicals begins to exhibit most of the behavior patterns that we associate with life. A virus, for example, may consist of fewer than 100 associated large molecules. It is the structures of these molecules and the ways in which they are associated that determine a virus’ behavior and make it appear to be on the threshold of life.
This chapter is devoted to a consideration of the chemical elements found in living systems, and how these elements combine to form molecules and collections of molecules which carry out the biological functions and behaviors that we associate with life. Our treatment must of necessity be brief, but even if it were not, the complexity of biochemical systems would insure that it would be incomplete. Much of the future of chemistry, both inorganic and organic, will involve the extension to complex biological systems of principles and facts gleaned from studies of the much simpler chemical behavior we have described in previous chapters.
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