Bio 111 Enzymes
[email protected] enzymes are catalysts: increase the rate of a specific chemical reaction. in biology, most enzymes are proteins (a few are RNAs) a chemical reaction, where the reactant is called the “substrate”: substrate + enzyme <> enzymesubstrate complex > product + enzyme S + E <> S noncovalently bound to E > P + E enzymes increase reaction rates by lowering the activation energy “barrier” between S and P the enzyme gives the reaction an "easier path" from S > P a path from S > P that travels via a lower energy intermediate form some mechanisms by which enzymes lower activation energy: proper orientation of substrate molecules "strain" covalent bonds of substrate molecule enzymes do NOT change a reaction’s thermodynamics: ∆G is unchanged, K is unchanged eq enzymecatalyzed reactions have nonlinear saturation kinetics, where V = f([S], K , V ) m max nonprotein parts of enzymes: required for many enzymes to function participate in the catalysis mechanism temporarily or permanently bound to the active site of the enzyme 2+ 2+ cofactors = metal ions, e.g. Mg , Fe used by many enzymes that catalyze redox reactions coenzymes = nonprotein organic molecules, e.g.: vitamin B6 coenzyme A = CoA, functions as an acetyl group carrier (a carrier of a twocarbon group) NAD, nicotinamide adenine dinucleotide, functions as an "electron carrier"
vitamin B6
CoA
NAD