This chapter is a brief overview of the general information about the main classes of enzymes and its applications. The key enzymatic systems involved in the conversion of solar energy into chemical energy, the formation of energy-rich molecules, carbon dioxide, and atmospheric nitrogen fixation, the synthesis and degradation of amino acids, lipids, proteins, nucleotides, and nucleic acids. Enzymes provide vital chemical reactions like oxidative phosphorylation, Krebs cycle, Glycolysis Calvin-Benson cycle. Several paragraphs are devoted to miscellaneous enzymes including cytochromes P450, methane monooxygenases, hydrolases, kinases, and phosphatases. Enzymes play a vital role for all living things and control all normal and pathological processes. Enzymes in healthcare and medicine are used for treating disorders, assisting metabolism, medical device cleaning, the manufacture of medicines, regulation of digestion, detection of diseases, addressing food quality, treating heart, brain, lung, digestive tract, and mental diseases. Separate sections refer to the crucial role of enzymes in cancer and in COVID-19. Enzymes are widely used in such practically important areas as pharmaceutical industries, yogurt, beer and cheese production, apple wine fermentation, baking, brewing, production of cakes, preparation of digestive aids, fruit juices, and starch syrups and addition to the dough of bread, biodiesel production, enzymatic degumming, textile and paper industry, textile desizing, laundry detergents, the enzyme-mediated ceramic synthesis, skincare and cosmetics industry, the enzyme-mediated ceramic synthesis, the enzymatic decomposition of organic matter in soil. Thus, modern enzymology represents an inexhaustible source of knowledge and ideas for modern chemistry to initiate and bring about the real industrial revolution of the twenty-first century.
