Nine - Reactions

Nine - Reactions - Reactions What will happen?...

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2/17 and 2/20/12 MCB 2000 Lectures 10-12 Reactions • What will happen? Thermodynamics predicts the direction of a chemical reaction. • How fast will the reaction occur? Even if a reaction has a favorable G and can occur spontaneously, the rate may be too slow for a metabolic process.
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2/17 and 2/20/12 MCB 2000 Lectures 10-12 Lecture Outline • Properties of enzymes • Determinants of reaction rates • How does an enzyme increase the rate of a reaction? • Michaelis-Menten rate equation: assumptions and predictions
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2/17 and 2/20/12 MCB 2000 Lectures 10-12 General Properties of Enzymes • Specificity —how is this achieved? • Catalysis —how is reaction rate increased? Factors that affect catalysis • Regulation —Most reactions in cells do not occur at a constant rate. Why
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2/17 and 2/20/12 Specificity Specificity is controlled by structure - the unique fit of substrate with enzyme controls the selectivity for substrate and the product yield MCB 2000 Lectures 10-12 Trypsin Thrombin
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2/17 and 2/20/12 MCB 2000 Lectures 10-12 Specificity is controlled by structure Active site can contain amino acids from different positions in the linear sequence of amino acids. Lysozyme
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2/17 and 2/20/12 MCB 2000 Lectures 10-12 Enzymes are (stereo)specific. Noncovalent interactions stabilize substrate binding
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2/17 and 2/20/12 MCB 2000 Lectures 10-12 Binding of substrate to the active site can occur as “lock and key” or “induced fit”. This is an example of induced fit— significant conformational change occurs Glucokinase
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2/17 and 2/20/12 MCB 2000 Lectures 10-12 E + + E Enzyme Catalysis S P Enzymes return to their original conformation. They are catalysts and are not used up during the reaction .
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NOTE: Amount of product formed is the same ± enzyme 2/17 and 2/20/12 MCB 2000 Lectures 10-12 Enzymes DO NOT alter G  or K eq Accelerate the attainment of equilibria but do not shift the position. Equilibrium position is a function of the free energy difference between reactants and products. Equilibrium reached
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2/17 and 2/20/12 MCB 2000 Lectures 10-12 How can the rate of a reaction be measured?
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MCB 2000 Lectures 10-12 Relationship between substrate concentration and reaction rate (velocity) Rate of catalysis = number of moles of product formed per unit of time Conditions: Constant [E] Vary [S] Initial velocity (slope) determined early in reaction
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This note was uploaded on 03/19/2012 for the course BIO 2000 taught by Professor Ewr during the Spring '12 term at Alabama.

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Nine - Reactions - Reactions What will happen?...

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