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Transcript
ENZYMES ENZYMES ARE PROTEINS Polymers of amino acids Heat-sensitive Absorb light at 280 nm ENZYMES ARE CATALYSTS Reaction accelerators Lower energy of activation of reactions Stabilize the transition state Not consumed in the reaction There are two components to a chemical reaction: (1) its kinetic or rate component, and its thermodynamics, or energy component. When we deal with enzymes, we are concerned primarily with the rate component. Do’s and Don’t’s for Enzymes Do 1. Lowers energy of activation of forward and reverse reactions 2. Speeds up the time required to reach equilibrium or completion 3. Stabilizes the Transition State 4. Conducts a specific reaction with no side products DON’T’S 1. Changes the DG of a Reaction 2. Changes the Equilibrium Position of a Reaction 3. Changes the Energy Yield (or requirement) of a Reaction STOP ENZYME TALK 1. Enzyme: A protein or RNA molecule that has the property of a catalyst, sometimes called a biocatalyst. 2. Substrate: The target of the enzyme’s action. The molecule that will undergo chemical change as a result of the enzyme 3. Enzyme activity: A measure of the enzymes catalytic effectiveness as manifested by the rate of the reaction catalyzed. 4. Cofactor: A component that works with the enzyme in effecting catalysis. Literally, any chemical factors the assists the activity of an enzyme-catalyzed reaction. 5. Coenzyme: Related to cofactor, but generally used to describe molecules that are derived from B-vitamins. 6. Enzyme kinetics: A branch of enzymology that deals with mechanism as studied by factors that affect the rate of enzyme reactions. 7. Active Site: That region on the enzyme surface or within a crevice where the substrate binds and catalysis is performed. HA-HB + B + HA + HB-B + Transition State Free Energy DG HA-HB + B Free energy of Activation HA + HB-B Reaction Coordinate No change in free energy of reaction HA-HB + B Free energy of activation of forward reaction HB-B + HA DGf DGf Free energy change of reaction DG DGr Free energy of activation of reverse reaction DGr Reaction Coordinate Enzymes low the energy of activation of both forward and reverse reactions. They do not affect the overall free energy Multiple Step Reactions (multi-transition States) A+B D-glucose + CH3OH (open chain) [A*] A + B [-D-glucose] Methyl-D-glucoside (hemiacetal) Two Steps Slow step (Rate-determining) A+B DG A* (hemiacetal) A-B (methyl-D-glucoside) A B Transition state Energy of activation of forward uncatalyzed reaction Energy DG A B A Equilibrium B position Reaction Coordinate A reaction at equilibrium requires energy to move the reaction off the equilibrium position ENZYME CLASSIFICATION 1. TRIVIAL 2. REACTION TYPE AND SUBSTRATE 3. SYSTEMATIC NOMENCLATURE TRIVIAL (Oldest) Digestive Fluids, Bacteria, Plants Trypsin Chymotrypsin Pepsin Cathepsin Lysozyme Papain Thermolysin Appearance Old Yellow Enzyme - Otto Warburg Kuhn’s “enzyme” meaning “in yeast” SUBSTRATE - REACTION TYPE 1. Enzymes given “ase” suffix 2. Substrate first, then reaction type Example CH3CH2OH CH3CHO Product is an aldehyde Substrate is alcohol Reaction removes hydrogen atoms ALCOHOL DEHYDROGENASE PROBLEM: TOO MANY REACTIONS TYPES Dehydrogenases Proteases Lipases Esterases Acyltransferases Deaminases Reductases Glycosidases Synthetases Isomerases Synthases Epimerases DNAses Amylases RNAses Peptidases Nucleosidases ENZYME CLASSIFICATION Systematic Nomenclature 1.0 OXIDOREDUCTASES 2.0 TRANSFERASES 3.0 HYDROLASES 4.0 LYASES 5.0 ISOMERASES 6.0 LIGASES SYSTEMATIC NOMENCLATURE CH3CH2OH NAD+ CH3CHO + NADH + H+ EC1.1.1.1. To see why, study the Table below. 1. Oxidoreductases (oxidation-reduction reactions of all types) 1.1 1.1.1 1.1.1 acting on CH-OH group of substrates requires NAD+ or NADP+ as hydrogen acceptor specific substrate is ethyl alcohol 1.0 Oxidoreductases: (Add or remove electrons) 2.0 Transferases (Transfer group to substrate) CH2OH HO-C-H CH2OH + ATP CH2OH Glycerol Glycerol phosphate 3.0 Hydrolases (Cleave bonds with H2O) CH2OH CH2OH HO-C-H CH2OPO3= + ADP HO-C-H CH2OPO3= + H2O Glycerol phosphate HO-C-H CH2OH Glycerol + HPO4- 4.0 LYASE (split C-X without water; reverse forms bond without a need for energy ) CH2OPO3 C=O CH2OPO3 C=O HO-C-H split HO-C-H H-C-OH H-C-OH CH2OPO3 unite Dihydroxyacetone phosphate H O H H-C-OH C Glyceraldehyde-3-phosphate CH2OPO3 Fructose 1,6 bisphosphate Split product of the forward or one substrate of the reverse reaction must have a double bond 5.0 ISOMERASES (change groups around) COOH H C OH CH2OPO3 3-phosphoglycerate CH2OPO3 OH H HO OH H OH H OH glucose 6-phosphate COOH H C OPO3 CH2OH 2-phosphoglycerate CH2OPO3 O CH2OH H HO H H HO H fructose 6-phosphate 6.0 LIGASES (tie together…need energy) CH3 C S CoA + HCO3 + ATP O acetyl-CoA Synthetases Synthases HOOC CH2 C S CoA + ADP + HPO4 O malonyl-CoA Use ATP No ATP Caution: Synthases could be Lyases