103Lect10Sp10powerpoint

103Lect10Sp10powerpoint - Lecture 10: Enzyme Regulation or...

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Lecture 10: Enzyme Regulation Why are enzymes activities regulated? How are enzymes regulated? Which enzymes are regulated? Many examples……. or When do they do what they do ?
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Concepts of Enzyme Regulation and Reciprocal Regulation AND Mechanisms for the Regulation of Enzymatic Reactions Why are enzyme reactions regulated? 1. To produce products only when needed. 2. There are lots of pathways in the cell, some of which are opposing in direction (one produces a compound, the other pathway metabolizes that compound). In general, opposing pathways do not occur at the same rate, at the same time. If they did, then no net product would be produced, but in many cases ATP and/or NADH would be consumed. This is called futile cycling . Regulating enzyme activity prevents futile cycling and prevents the synthesis of unneeded or excess products. HB 45 Also called Substrate Cycling
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Exceptions: heat generation, ATP hydrolysis releases energy as heat
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Partial exception: having opposing steps occur allows greater control over the flux- PARTIAL FUTILE CYCLING. PARTIAL FUTILE CYCLING IS VERY COMMON USEFUL IN REGULATING FLUX
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IN GENERAL: To prevent futile cycling, enzymes of opposing irreversible reactions are regulated in opposite directions. HB 45 complete
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HOW IS METABOLIC FLUX REGULATED? A. Regulate amount of Substrate B. Regulate activity of Enzyme via changes in: 1. Enzyme amount (synthesis vrs degradation) 2. Type of enzyme present- (isozymes with different catalytic properties) 3. Enzyme specific activity (see below), changing activity of the same amount of enzyme. A major mechanism of enzyme regulation is regulating enzyme specific activity HB 45
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There are two main types of mechanisms for regulation of enzyme specific activity HB 45
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1 . Allostery- Enyzme activity can be activated or inhibited through non-covalent interaction of the enzyme with small molecules called effectors, modulators, or allosteric regulators. Effectors bind to the enzyme at a site other than the active site (allo means other). Reversible binding to enzyme- fast response time. Concentration dependent. HB 45 common allosteric regulators- 1. ATP, ADP, AMP, NAD/NADH, CoA 2. End-product of a pathway- when inhibits feedback inhibition 3. Substrate of the enzyme 4. Product of the enzyme reaction- feedback inhibition
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2. Covalent modification - Covalent addition of a group to an enzyme changes the activity of the enzyme. HB 45 Typically requires enzyme to catalyze attachment and removal. Not concentration dependent, but modifying enzymes are regulated.
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Mechanisms of Reciprocal Regulation: To prevent futile cycling, regulation of enzyme activity by allostery or covalent modification works reciprocally. That is, the specific activities of one or more enzymes of a pathway are activated at the same time the specific activity of one or more enzymes of the opposing pathway is inhibited.
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103Lect10Sp10powerpoint - Lecture 10: Enzyme Regulation or...

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