MICROBIOLOGY - M.H. Serhiichuk - 2008

Chapter 5. MICROBIAL METABOLISM

INTERRELATIONSHIP OF MICROBIAL CHEMICAL REACTIONS

METABOLISM (Greek metabole - turning about, change) is the sum of various oxidation, reduction, Cleavage, and synthesis Chemical Reactions that occur with the participation of specific enzyme systems and ensure the vital activity, development, and reproduction of an Organism. Metabolism is the net result of two interconnected processes: Catabolism and anabolism.

Catabolism (Greek katabole - a throwing down) is the set of enzymatic reactions associated with the breakdown (oxidation) of a substrate into simple end products, accompanied by The formation of reduction equivalents and the release of energy stored in ATP and other energy-rich compounds. The primary purpose of catabolic reactions is to supply The Cell with energy.

Anabolism (Greek anabole - a rising up, ascent) is the set of energy-dependent biochemical processes aimed at the synthesis of simple molecules, polymers, and structural cell components. Anabolic processes are accompanied by The oxidation of reduction equivalents and the Hydrolysis of ATP. The primary purpose of anabolic reactions is Biosynthesis.

Some Catabolic pathways, In addition to degrading complex compounds to generate ATP and reduction equivalents, perform an additional function: they supply simple molecules (key metabolites) for biosynthesis. Key metabolites are generated during catabolic reactions and partially utilized in anabolic reactions. Catabolic pathways that supply key metabolites for biosynthesis are called amphibolic pathways (Greek amphibolos - ambiguous). The replenishment of the key metabolite pool in cyclic processes occurs via anaplerotic reactions.

The connection between catabolism and anabolism is mediated through ATP, reduction equivalents, and key metabolites (Fig. 5.1).

Since ATP is synthesized in the cell via the phosphorylation of ADP (ADP + Ф_н + Н⁺ = АТФ + Н₂О), The process of ATP synthesis is often referred to as phosphorylation. There are two MAIN TYPES OF phosphorylation:

- substrate-level phosphorylation;

- electron transport phosphorylation (which includes Oxidative Phosphorylation AND Photophosphorylation).

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Fig. 5.1. Interrelationship between Catabolic and anabolic reactions

Substrate-level phosphorylation is the process of ATP synthesis resulting from The conversion of an organic substance from one form into another, such as in Glycolysis and the Krebs cycle. This is the most ancient and simplest mechanism for energy generation.

Electron transport phosphorylation is the synthesis of ATP by ATP synthase driven by a proton gradient and Membrane Potential. This more complex process occurs during Respiration (oxidative phosphorylation) in chemoorganotrophic and chemolithotrophic organisms, as well as during Cyclic electron transport in photosynthetic organisms (photophosphorylation).