Chapter06FALL05 - Chapter 6 - Enzyme Mechanisms...

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Chapter 6 - Enzyme Mechanisms Introduction All enzymatic reactions go through a transition state (unstable intermediate form with a structure between that of reactant and product). Reactants must collide precisely to form transition state. Must have correct orientation. Must collide with enough energy = activation energy = G Enzymes work by lowering G Substrates are correctly oriented. All increase probability of reaction. Transition states are stabilized. Chemical Catalysis Active site of most enzymes is lined with hydrophobic amino acids. There are a few polar a.a. which make up the catalytic center of the active site and can be ionized. Histidine (basic a.a.) is common. Aspartate and glutamate - negatively charged Lysine and arginine - positively charged; electrostatic binding can occur There are several types of chemical catalysis: 1) acid-base catalysis Enzymes that use this have a.a. side chains that can donate or accept electrons to substrate. Can accelerate a chemical reaction by a factor of 10-100. 2) covalent catalysis Substrate forms a covalent bond with enzymes, then part of substrate is transferred to a second substrate in a 2 step process. A-X + E X-E + A X-E + B B-X + E 3) proximity effect Collection of substrate molecules in the active site increases the concentration over those molecules found freely in solution.
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Result is that there is a more frequent formation of transition states. 4)
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This note was uploaded on 08/02/2009 for the course BIOCHEMIST 100 taught by Professor Crew during the Spring '05 term at North Alabama.

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Chapter06FALL05 - Chapter 6 - Enzyme Mechanisms...

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