Section4_enzymes_09

Section4_enzymes_09 - Enzymes Enzymes Catalyst: A substance...

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1 Enzymes Enzymes Catalyst : A substance that speeds up the rate of a chemical reaction but is not itself consumed. Most biological catalysts are proteins, enzymes . A few catalysts are RNA: peptide bond formation is catalyzed by RNA in ribosomes. Some enzymes require organic coenzymes and or metal ions. Apoenzyme / Apoprotein = Protein Holoenzyme = Protein + Coenzyme
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2 Enzymes Classification of Enzymes Add “-ase” to the activity to obtain the name. 1. Oxidoreductases : transfer e - as H or H - 2. Transferases : transfer groups between molecules 3. Hydrolases : add functional groups to water 4. Lyases : form or add to double bonds. 5. Isomerases : isomerize by group transfer 6. Ligases : form C-C, C-S, C-O, C-N bonds, coupled to ATP cleavage Enzymes Why are enzymes necessary? 1. Enzymes catalyze chemical reactions. They can accelerate bond formation and breakdown by 10 6 -10 12 2. Enzymes are responsible for the majority of all reactions in living systems. 3. Enzymes are very specific ; no side-reactions. 4. Enzymes can be regulated.
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3 Enzymes Our discussion of enzymes will be organized into three sections: 1. Thermodynamic background to catalysis 2. Mechanisms of catalysis 3. Kinetics of catalysis Enzymes Fundamental terms and ideas for enzyme catalysis: a) Substrate (S) : the reactant on which the enzyme acts, to convert it to the product (P) in many cases, two (or even more) substrates react together; there may be two or more products b) Enzyme-substrate (E.S) complex : a non-covalent, reversible association between enzyme and substrate catalysis occurs in the E.S complex c) Active site : the pocket on the enzyme where the substrate binds and the reaction is carried out
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4 Enzymes (same structure; two representations) Enzymes We formulate the uncatalyzed reaction as: S S P and the enzyme-catalyzed reaction as: S + E E.S E.S E.P E + P Here, the double dagger symbol ( ) refers to an activated state of increased energy (the transition state) , which reactants must pass through on their way to the products. E.S and E.P are the non-covalent complexes between enzyme and substrate or product.
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5 Enzymes Transition state theory is a useful way to analyze what is needed for catalysis to occur. The rate of a chemical reaction depends on how much energy the reactant (or substrate) must acquire in order to reach the transition state. In general: reaction rate = (constant) T e - G ! /RT Here, G is the activation energy , the extra energy that S must acquire to reach the transition state S . S is of higher energy than S because S must undergo distortion (bond stretching or bending, locking in a rare conformation) in order to react Enzymes
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6 Enzymes Since the enzyme catalyzes the reaction (makes it go faster), it must somehow reduce the activation energy.
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This note was uploaded on 02/27/2011 for the course MBIO 2370 taught by Professor Spearman during the Winter '11 term at Manitoba.

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Section4_enzymes_09 - Enzymes Enzymes Catalyst: A substance...

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