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Understanding Enzymes: Catalysts in Biochemical Reactions

Enzymes are crucial biological catalysts that lower activation energy, facilitating chemical reactions. Their active sites consist of specific side chain groups, influenced by electrostatic forces, van der Waals forces, and hydrogen bonding, enhancing substrate binding. Enzymes may exert various functions such as orienting reactants, forming unstable intermediates, and acting as proton donors or acceptors. The reaction rate depends on enzyme and substrate concentration, where Vmax represents maximum reaction rate under substrate saturation. Michaelis-Menten kinetics describe enzyme-substrate affinity and efficiency.

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Understanding Enzymes: Catalysts in Biochemical Reactions

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  1. SPECIAL REVIEW TOPIC: ENZYMES AND • ENERGETICS • ENZYMES ARE CATALYSTS THAT LOWER ACTIVATION ENERGY AND ASSIST REACTIONS TO OCCUR • THE ACTIVE SITE CONISTS OF SPECIFIC SIDE CHAIN GROUPS WHICH ARE BROUGHT INTO CONFROMATION BY FORCES OF ELECTROSTATIC BONDING, VAN DER WAALS FORCES, HYDROGEN BONDING • MANY IONIZABLE SIDE GROUPS ARE EXPOSED IN THE ACTIVE SITE. THIS MAY HELP THE BINDING PROCESS

  2. ENZYMES MAY EXERT THE FOLOWING ACTIVITIES: • MAY HOLD REACTANTS IN A SPECIFIC ORIENTATION • MAY REACT DIRECTLY WITH SUBSTRATE TO FORM UNSTABLE INTERMEDIATE THAT RAPIDLY ENTERS INTO SECOND REACTION AND YIELDS PRODUCT

  3. ENZYMES MAY EXERT THE FOLOWING ACTIVITIES: • SIDE GROUPS MAY ACT AS PROTON DONORS AND ACCEPTORS AND FACILITATE ACID-BASE REACTIONS • BINDING MAY CAUSE BBOND STRESS, INCREASING PROBABILITY BONDS WILL BREAK AND FACITITATE REACTION

  4. TEMPERATURE AND ACID –BASE STATUS ARE IMPORTANT FACTORS • COFACTORS ARE USUALLY NECESSARY • ALLOSTERIC ACTIVATION OR INHIBITION CAN OCCUR

  5. ENZYME KINETICS • THE RATE AT WHICH A REACTION PROCEEDS IS DEPENDENT UPON THE CONCENTRATION OF ACTIVE ENZYME, SUBSTRATE AND PRODUCT • RATE OF CONVERSION • WHERE: [A]= INSTANTANEOUS CONCENTRATION OF SUBSTRATE K= rate constant -d[A]/dt = RATE AT WHICH A IS CONVERTED TO P

  6. FIRST ORDER REACTION =WHEN RATE OF CHANGE OF A QUANTITY IS PROPORTIONAL TO THE INSTANTANEOUS VALUE OF THE QUANTITY THERE ARE ALSO ZERO ORDER AND SECOND ORDER KINETICS

  7. ENZYME SUBSTRATE AFFINITY • THE MAXIMUM RATE OF A REACTION ( VMAX) OCCURS WHEN ALL AVAILABLE ENZYME IS SATURATED WITH SUBSTRATE. THE ENZYME IS RATE LIMITING IN THIS CASE • ENZYMES DIFFER IN THEIR TURNOVER NUMBERS SO VMAX VARIES DEPENDENT ON THE GIVEN CONSTITUENTS

  8. Michaelis-menten Eqn For Rate Of A Single Enzyme Catalyzed Reation:

  9. WHERE: • Vo = initial reaction rate at substrate concentration [S] • Vmax= RXN RATE WITH EXCESS SUBSTRATE • Km= Michaelis- Menten constant; it depends on the affinity of the enzyme for the substrate- greater the affinity the lower the Km ; 1/Km is a measure of affinity of enzyme for substrate

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