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Enzymes continued • Some enzymes work together to complete a series of reactions to produce a given product: Enzyme 1 Enzyme 2 Enzyme 3 • A + B ------- C ------- D ------------ E • Collectively, these steps are known as a metabolic pathway A metabolic pathway The entire set of all chemical reactions being performed by an organism is called its metabolism • Anabolism = chemical reactions that expend energy to make or transform chemical bonds • Catabolism = chemical reactions that harvest energy by breaking chemical bonds Anabolism involves endergonic reactions Catabolism involves exergonic reactions Control of Metabolism • Coenzymes • Inhibitors • Allosteric regulation • Feedback Inhibition • Cooperativity Coenzymes • Coenzymes are bound at the active site in order to interact with the substrate and play an essential role in the catalysed reaction. • They act as carriers of a variety of chemical groups. . Most water-soluble vitamins are components of coenzymes Vitamin Thiamine (B1) Riboflavin (B2) Nicotinic acid (niacine) Coenzyme Deficiency Thiamine Beriberi (weight pyrophosphate loss,other problems Mouth lesions, FAD+ dermatitis Pellagra (dermatitis, + NAD depression) Pantohtinic acid Coenzyme A Hypertension Biotin Biotin Rash, muscle pain Inhibitors • Specific for an enzyme • Can be reversible or non-reversible • Competitive inhibitors • Non-competitive inhibitors Competitive vs. Non-competitive inhibitors Many inhibitors are used as pesticides or drugs Regulating the rates of enzymedriven reactions • Cells use inhibitors and activators to turn off and on enzymes • Many enzymes are controlled by an allosteric site remote from the active site Allosteric regulation of enzyme activity Many allosterically controlled enzymse show quaternary structure Feedback inhibition Many enzymes are actually regulated by the end products of the reaction they catalyze Enzyme 1 Start of pathway X Enzyme 2 Intermediate Intermediate Enzyme 3 Product Presence of product inhibits enzyme 1 This prevents too much product from being made An example of Feedback inhibition