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REGULATION OF METABOLISM - b Repress(inhibit enzyme...

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REGULATION OF METABOLISM (ENZYME ACTIVITY) Two groups enzymes A. Constitutive enzymes - produced continually B. Inducible - produced as needed, in presence of substrate Two types of control mechanisms: A. Feedback inhibition - negative feedback system 1. Regulates enzyme activity 2. End product of pathway reacts with enzyme (allosteric enzyme) catalyzing first reaction in pathway 3. Shape of the active site of the enzyme changed no longer complementary to combining site on the substrate 4. Reaction inhibited until concentration of end product decreases 5. End product no longer reacts with allosteric site on enzyme 6. Active site on enzyme returns to shape complementary to substrate reaction occurs B. Operon - genetic control 1. Regulates enzyme production 2. Genes in DNA that : a. Induce enzyme production in the presence of the substrate
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Unformatted text preview: b. Repress (inhibit) enzyme production in the absence of the substrate 3. Operon consists of: a. Regulator gene – codes for repressor protein b. Operator gene – binding site for repressor protein c. Promoter gene – binding site for RNA polymerase 4. Lac operon a. In absence of lactose: 1). Repressor protein binds to operator gene 2). RNA polymerase cannot bind to promoter gene 3). Production (transcription) of enzymes required for lactose metabolism prevented b. In presence of lactose: 1). Lactose molecules bind to repressor protein → inactivated 2). Inactive repressor protein cannot bind to operator gene 3). RNA polymerase binds to promoter gene → transcription 4). Production enzymes required for lactose metabolism 4. See operation of Lac operon in figure in text...
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