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Genes, the environment, and the organism
The net outcome of the reading of a gene is that a protein is made that generally has one of two basic functions, depending on the gene. First, the protein may be a structural protein, contributing to the physical properties of cells or organisms. Examples are microtubule, muscle, and hair proteins. Second, the protein may be an enzyme that catalyzes one of the chemical reactions of the cell. Therefore, by coding for proteins, genes determine two important facets of biological structure and function. However, genes cannot dictate the structure of an organism by themselves. The other crucial component in the formula is the environment. The environment influences gene action in many ways, about which we shall learn in subsequent chapters. In the present context, however, it is relevant to note that the environment provides the raw materials for the synthetic processes controlled by genes. For example, animals obtain several of the amino acids for their proteins as part of their diet. Most of the chemical syntheses in plant cells use carbon atoms taken from the air as carbon dioxide. Bacteria and fungi absorb from their surroundings many substances that are simply treated as carbon and nitrogen skeletons, and their enzymes convert these components into the compounds that constitute the living cell. Thus, through genes, an organism builds the orderly process that we call life out of disorderly environmental materials
