Virtually everyone knows that the genes, located in the nuclei of all cells of the body, control heredity from parents to children, but most people do not realize that these same genes also control day-to- day function of all the body’s cells. The genes control cell function by determining which sub- stances are synthesized within the cell—which struc- tures, which enzymes, which chemicals.Figure 3–1 shows the general schema of genetic control. Each gene, which is a nucleic acid called deoxyribonucleic acid (DNA), automatically controls the formation of another nucleic acid, ribonucleic acid (RNA); this RNA then spreads throughout the cell to control the formation of a specific protein. Because there are more than 30,000 different genes in each cell, it is theoreti- cally possible to form a very large number of different cellular proteins.Some of the cellular proteins are structural proteins, which, in association with various lipids and carbohydrates, form the structures of the various intracellu- lar organelles discussed in Chapter 2. However, by far the majority of the pro- teins are enzymes that catalyze the different chemical reactions in the cells. For instance, enzymes promote all the oxidative reactions that supply energy to the cell, and they promote synthesis of all the cell chemicals, such as lipids, glyco- gen, and adenosine triphosphate (ATP).
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