ABSTRACT
In order to grow and to replicate, life forms depend on chemical elements and simple molecules from which they build their cellular components. This bottom-up synthesis of molecules is termed “anabolism,” defined as the totality of biochemical pathways that build more complex biomolecules from simpler precursors. Anabolism comprises a wide variety of pathways involving numerous enzymes and biosynthetic intermediates. At its core, anabolism is intricately linked to catabolism discussed in the last chapter. In particular, catabolism provides the chemical energy needed for anabolic reactions as well as central intermediates that serve as precursors to more complex biomolecules. For example, tricarboxylic acid (TCA) cycle enzymes not only generate the reduced coenzymes nicotinamide adenine dinucleotide (NADH), nicotinamide adenine dinucleotide phosphate (NADPH) and flavin adenine dinucleotide (FADH2) during catabolic processes that are subsequently used for adenosine triphosphate (ATP) production, but several TCA intermediates serve as precursors for amino acids and other biosynthetic products in anabolic routes. This dual role of the TCA cycle illustrates the inseparable relationship between catabolic and anabolic processes in cellular metabolism. This chapter will first examine the relationship of ana- and catabolism, discuss how inorganic carbon and nitrogen are converted to cellular metabolites, and finally provide an overview of biosynthetic principles underlying the production of the substance classes carbohydrates, fatty acids, amino acids, and nucleotides.
