BIOCHEMISTRY - Textbook - Ostapchenko L. I. - 2012

Chapter 16. ENERGY METABOLISM

Living organisms are continuously and inextricably linked with their environment. This connection is maintained through METABOLISM, which comprises three stages: the intake of substances into the Organism; metabolism proper; and The excretion of end products from the organism.

The intake of substances occurs via Respiration (oxygen) and Nutrition. Within the gastrointestinal tract, food products undergo Digestion (being broken down into simple substances). This process involves the Hydrolysis of polymers (Proteins, Polysaccharides, and other complex Organic compounds) into monomers, which are then absorbed into the Blood AND Lymph, and incorporated into Intermediary Metabolism (intracellular metabolism). The latter encompasses Two Types of reactions: Catabolism and anabolism (Fig. 16.1).

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Fig. 16.1. General scheme of metabolic and energy exchange:

1 - digestion; 2 - catabolism; 3 - anabolism; 4 - breakdown of Structural and functional Cell components;

5 - exergonic reactions; 6, 7 - endergonic reactions; 8 - excretion from the organism

Catabolism is The process of breaking down organic molecules into end products. In mammals, including humans, the End products of organic compound metabolism are СО2, Н2О, and urea. Catabolic processes involve metabolites generated both during digestion and through the degradation of structural and functional cellular components. Catabolic reactions are accompanied by the release of energy.

Anabolism encompasses BIOSYNTHETIC PROCESSES IN which simple building blocks are joined together to form complex macromolecules necessary for the normal physiological activity of the organism. Anabolic reactions utilize The energy released during catabolism.