ABSTRACT
The elementary unit of metabolism is the biochemical reaction where a substrate is transformed into a product through the catalytic action of a specific enzyme. More than 3,000 different enzymes must be synthesized for the self-replication of a bacterial cell. A metabolism is the system of biochemical reactions in a living organism or microbial community. The seven classes of enzymes are: (1) oxidoreductases, which catalyze oxidation–reduction reactions; (2) transferases, which catalyze transfers of different chemical groups between molecules; (3) hydrolases, which catalyze hydrolysis reactions; 4) lyases, which catalyze the cleavage of C–C, C–O, C–S, and C–N bonds by means other than hydrolysis or oxidation; (5) isomerases, which catalyze rearrangements of isomers; (6) ligases, which catalyze the reactions of biosynthesis where two molecules are joined; and (7) translocases, which catalyze the translocations across the cellular membranes of the protons (hydrons), cations and anions, molecules of amino acids, and carbohydrates. The main metabolic blocks are catabolism (oxidation–reduction coupled with energy generation) and anabolism (biosynthetic reactions coupled with energy utilization). The mechanisms of control have been described above. There are different mechanisms to control the enzyme activity and the activity of metabolic blocks at the levels of cells, cell aggregates, multicellular organisms, or populations of microorganisms. A tutorial with solutions and a quiz bank are added to this chapter.
