ABSTRACT
This chapter examines the major catabolic and anabolic pathways. It also examines why lipids possess a greater number of calories on an anhydrous basis than do either carbohydrates or proteins. Carbohydrates in the typical American diet contribute 51% of the total dietary calories consumed; lipids, typically fats and oils, contribute 34% of total calories; and protein contributes the remaining 15% of calories consumed. Glycolysis occurs in vivo under either aerobic or anaerobic conditions. With purely aerobic conditions, pyruvate is oxidatively decarboxylated and transformed into acetyl-coenzyme A, the most important metabolic intermediate common to the catabolism of carbohydrates, fatty acids, and amino acids. Acetyl-coenzyme A condenses with oxaloacetate, forming citric acid in the initial metabolic step of the citric acid cycle, whereby the catabolism of glucose is continued. The chapter also explores how and where adenosine triphosphate is synthesized in the mitochondria of plants, bacteria, animals, and humans by oxidative phosphorylation.
