2. We have covered several factors that allow an enzyme to lower the free energy

Question

2. We have covered several factors that allow an enzyme to lower the free energy of activation of a reaction. Each of the experimental observations below provides support for one of these factors. Identify the factor A. The acetylcholinesterase-catalyzed hydrolysis of acetylcholine proceeds via two steps: (1) the formation of an acyl-enzyme intermediate between an active-site serine and the acetyl group of acetylcholine;, and (2) the hydrolysis B. The binding of Phe-Ply to chymotrypsin leads to the twisting of the planar C. During the reaction catalyzed by lactate dehydrogenase, NADH and pyruvate D. A mutation in chymotrypsin replaces ASP 102 (the one in the active site) with E. The irreversible inhibitor, diisopropylfluorophosphate attaches to SER 195 in of the acyl-enzyme intermediate. peptide bond. are bound adjacent to one another at the active site. isoleucine. This renders the enzyme catalytically inactive. chymotrypsin.

Explanation / Answer

Formation of intermediate is the factor responsible here. Intermediate state has a higher free energy compared to the energy of reactants and products. Therefore, the intermediates are less stable than reactants and products hence readily convert to the product by lowering activation energy. In this case by providing correct orientation between reactants there is a close contact of the reactant to the catalytic site. Due to which it reduced the contribution of the considerable activation entropy, due to the loss of the reactants' translational and rotational entropy, towards the total activation energy. In this case the activation energy is lowered because of close proximity of the reactants which led them to react without any external energy. so it provides more entropy and lowers activation energy. The mutation causes the replacement of ASP to isoleucine, isoleucine is aliphatic long chain amino acid, due to which there will be conformational change in the active site of the enzyme. This sterically hindered site seems to be inactive. Due to presence of more than one catalytic site, there is negative allosteric effect in which the inhibitor binds to the other active site, inhibiting the overall reaction.

Related Questions

Navigate

• Browse (All)
• Browse 2
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.