Lect26.EnzymePrinciples

Lect26.EnzymePrinciples - LECTURE 4: Principles of Enzyme...

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LECTURE 4: Principles of Enzyme Catalysis Reading: Berg, Tymoczko & Stryer: Chapter 8 An ENZYME ENZYME is a biomolecular catalyst that accelerates the rate of a specific reaction Enzymes DO NOT make a chemical reaction more energetically favorable; They only ACCELERATE the rate of the reaction towards its energetic equilibrium Enzymes work by stabilizing chemical transition states, the high-energy intermediates that normally act as a barrier to spontaneous reaction Most enzymes are FOLDED PROTEINS : proteins have the ability to fold into scaffolds with binding surfaces for substrates that position the substrates for chemical reaction A few enzymes are RNA molecules! RNAs also have ability to adopt tertiary structures. Some RNAs (called RIBOZYMES) act as enzymes catalyzing their own site-specific cleavage or that of other RNA molecules As catalysts, enzymes are NOT CONSUMED during reactions. S + E -----> ES -------> P + E In some cases, enyzmes are chemically modified during catalysis, but return to their original form after reaction cycle to allow further catalysis of substrate S + E -----> E*S -------> P + E
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Proteases Are Examples of Enzymes That Catalyze An Energetically Favored Process Fig 8.0new (peptide hydryolys) Peptide hydrolysis is an energetically favorable process, but normally occurs very slowly. PROTEASES are enzymes that catalyze peptide hydrolysis. Some proteases are rather NONSELECTIVE (e.g., papain) Other proteases are VERY SELECTIVE (e.g., trypsin, thrombin, fibrin) Fig 8.1new
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Some Enzymes Employ Cofactors Some enzymes use cofactors as part of the active site in enzymatic catalysis APOENZYME + COFACTOR --------> HOLOENZYME Many cofactors cannot be synthesized by humans, and must be obtained through diet as vitamins and minerals Tab8.2new
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Free Energy of Biochemical Reactions For reaction A + B C + D G is the differential in free energy between the products vs. reactants If G < 0 , reaction is energetically favorable I.e., reactants will convert to products as system moves to equilibrium If G = 0 , reaction is already at equilibrium I.e., there will be no NET conversion of reactants to products If G > 0 , reaction is disfavored I.e., products will convert to reactants as system moves to equilibrium;
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This note was uploaded on 02/14/2012 for the course BIO 710L taught by Professor Goldfarb during the Fall '10 term at Iowa State.

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Lect26.EnzymePrinciples - LECTURE 4: Principles of Enzyme...

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