Bacterial Cellular Metabolic Systems: Metabolic Regulation of a Cell System with 13C-Metabolic Flux Analysis

Book Preface

Metabolism describes the overall chemical or enzymatic reactions that occur in living organisms, which assimilate nutrients with high enthalpy and low entropy and gain free energy during the process of breakdown of nutrients into low enthalpy and high entropy substances, and thus keep the cells alive. All living organisms are in this irreversible state, and if this does not occur, the metabolic processes in the organism become in equilibrium, and the organism can no longer remain alive.

Let us defi ne the metabolite as the substrate, intermediate, or product of each metabolic reaction in the cell, and let the metabolic pathway be a series of metabolic or enzymatic reactions from the specific substrate to the specifi c product. Typical central metabolic pathways are shown in Figure 1.1 . When studying metabolic regulation or how cell metabolism is regulated, it is important to understand ‘catabolism’ and ‘anabolism C atabolism is defi ned as all chemical or enzymatic reactions involved in the breakdown of organic or inorganic materials such as proteins, sugars, fatty acids, etc. in order to obtain energy. Anabolism is defi ned as biosynthetic reactions that lead to the building of cell materials such as proteins, DNA, RNA, lipids, etc. from small molecules, such as pyruvate, produced along the main metabolic pathways using the energy obtained by the process of catabolism.

Briefly, the cell generates energy as ATP (adenosine triphosphate), typically along the glycolysis pathway, from glucose to low molecules such as pyruvate ( Figure 1.2 ). Moreover, the reducing equivalents, such as NADH and FADH 2 , produced at the glycolysis and TCA (tri carboxylic acid) cycle pathways are oxidized in the respiratory chain, where ATP is produced via the oxidative phosphorylation process. Namely, these energy generating processes are termed catabolism . Cell constituents, such as proteins, cell membranes, etc. are formed from their precursor metabolites, such as 3-phosphoglycerate (3PG), phosphoenol-pyruvate (PEP), and pyruvate (PYR) etc., by using the ATP produced by the process of catabolism. This is the anabolic process.