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Chapter 4 : Important Molecules in Microbes, Plants, and Animals
This chapter describes the most important chemical substances found in microbes. These substances are, in fact, the same classes of substances found in all types of cells. The terms molecules, carbohydrates, fats, proteins, DNA, are encountered daily in our lives: in newspapers, television advertisements, cereal box labels, and so on. The chapter examines some basic definitions and concepts of chemistry. A table in the chapter lists the elements of special importance in living matter, their relative weights (mass units), and their approximate abundance in the human body. The carbohydrates, fats, and proteins account for the major part of our foodstuffs, which we obtain mainly from plants and other animals. In cellulose, the glucose units are joined end to end, as in a linked chain. Glucose units can be joined together in other ways to produce polysaccharides with highly branched structures. There are two important examples of such large molecules (often referred to as macromolecules): glycogen, which occurs in animal muscle cells and in some microbes, and starch, which accumulates in certain plants. It is know that metabolism also involves interconversions of dietary components, for example, the transformation of carbohydrates into fats. The growth of microbes (as opposed to animals) rarely involves a digestive phase; rather, microbes are typically dependent on supplies of certain small molecules in their environment.