Chap_22_Enzymes and Metabolism

Chap_22_Enzymes and Metabolism - www ENZYMES AND METABOLISM...

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Unformatted text preview: www ENZYMES AND METABOLISM GENERAL FEATURES OF METABOLISM Metabolism : The coordinated chemical reactions that sustain life. There are two categories of such reactions: 1. Catabolism: the breaking down of molecules to generate energy. 2. Anabolism: The biosynthesis of molecules of living systems. Energy required by animals is generated mostly from lipids and carbohydrates. These fuel molecules must be oxidized to release energy. The oxidation process converts the fuel molecules into CO 2 and H 2 O. C 6 H 12 O 6 + 6O 2 6CO 2 + 6H 2 O + 686,000 cal C 16 H 32 O 2 + 23O 2 16CO 2 + 16H 2 O + 2340,000 cal STAGES OF CATABOLISM Stage I: carbohydrates, lipids and proteins are broken down into simple sugars, fatty acids, and amino acids respectively. Stage II: the products of stage I are further broken down via a specific pathway each, to a common end-product: Acetyl-CoA. Acetyl-CoA can be used in a myriad of biochemical pathways. Most importantly for energy generation, it proceeds to stage III. Stage III (Krebs cycle): Acetyl-CoA is completely oxidized to form CO 2 and H 2 O. These oxidation reactions lead to the synthesis of ATP. THE TRANSFORMATION OF NUTRIENTS CHEMICAL ENERGY INTO NEW FORMS Most of the energy conserved in the second and third stages of catabolism is used to synthesize three main compounds: ATP (adenosine triphosphate), NADH (nicotinamide adenine dinucleotide), and NADPH (nicotinamide adenine dinucleotide phosphate) ATP It is the energy currency of cells. It is the principal but not the only medium for energy exchange in biological systems. ATP synthesis takes place in two ways: oxidative phosphorylation and substrate-level phosphorylation. ATP is composed of the base, adenine, a ribose, and phosphates attached to C5 of the ribose. The most important characteristic of ATP is the pyrophosphate linkage. Pyrophosphate bonds are very high in energy (a lot of energy is needed to force the negatively charged groups to stay bonded to each other). When the bonds are broken, the molecule becomes more stable and releases energy....
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Chap_22_Enzymes and Metabolism - www ENZYMES AND METABOLISM...

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