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Chapter 14: Problem 17

At \(35^{\circ} \mathrm{C},\) the rate of the reaction catalyzed by enzyme \(\mathrm{A}\) begins to level off. Which hypothesis best explains this observation? a. The temperature is too far below optimum. b. The enzyme has become saturated with substrate. c. Both \(A\) and \(B\). d. Neither A nor B.

Short Answer

Expert verified
The most plausible explanation for the reaction rate beginning to level off at 35C is that the enzyme has become saturated with substrate (option b).

Step by step solution

01

Analyze the given options

Every option represents a different explanation for why the rate of the reaction is leveling off at 35 degrees Celsius. The task here will be to identify which of these four options is accurate.\na. The temperature is too far below optimum. \nb. The enzyme has become saturated with substrate. \nc. Both A and B. \nd. Neither A nor B.
02

Cross out the unlikely options

Option a) states the temperature is too far below optimum. In enzymatic reactions, the rate increases with temperature until an optimum temperature. Beyond this temperature, the enzyme starts to denature and the rate of reaction drops. Here the rate is leveling off, not dropping. So this can’t be the correct answer.\nOption d) Neither A nor B, this can be crossed out as we relayed that option a) isn't likely correct. This would only be correct if both option a) and b) were incorrect.
03

Choosing the correct answer

Option b) mentioned that the enzyme has become saturated with substrate. In an enzymatic reaction, the rate of reaction increases with increase in substrate concentration until a point where all enzymes are busy with substrates. Beyond this point, increasing substrate concentration doesn’t increase rate of reaction as no free enzymes are available to bind with extra substrates. Hence, the reaction rate levels off.\n\nThus, option b) provides a suitable explanation for the observation and hence can be considered as the correct answer for this question.

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Most popular questions from this chapter

As noted on page \(423,\) a true transition state can bind to an enzyme active site with a \(K_{\mathrm{T}}\) as low as \(7 \times 10^{-26} M .\) This is a remarkable number, with interesting consequences. Consider a hypothetical solution of an enzyme in equilibrium with a ligand that binds with a \(K_{\mathrm{D}}\) of \(10^{-27} M .\) If the concentration of free enzyme, \([\mathrm{E}],\) is equal to the concentration of the enzyme-ligand complex, [EL], what would \([\mathrm{L}],\) the concentration of free ligand, be? Calculate the volume of solution that would hold one molecule of free ligand at this concentration.

The \(k_{\text {cat }}\) for alkaline phosphatase-catalyzed hydrolysis of methylphosphate is approximately \(14 / \sec\) at \(\mathrm{pH} 8\) and \(25^{\circ} \mathrm{C}\). The rate constant for the uncatalyzed hydrolysis of methylphosphate under the same conditions is approximately \(10^{-15} /\) sec. What is the difference in the free energies of activation of these two reactions?

In which of the following environmental conditions would digestive enzyme Y be unable to bring its substrate(s) to the transition state? a. At any temperature below optimum b. At any pH where the rate of reaction is not maximum c. At any pH lower than 5.5 d. At any temperature higher than \(37^{\circ} \mathrm{C}\)

Tosyl-L-phenylalanine chloromethyl ketone (TPCK) specifically inhibits chymotrypsin by covalently labeling His \(^{57}\). Tosyl-L-phenylalanine chloromethyl ketone (TPCK) a. Propose a mechanism for the inactivation reaction, indicating the structure of the product(s). b. State why this inhibitor is specific for chymotrypsin. c. Propose a reagent based on the structure of TPCK that might be an effective inhibitor of trypsin.

An enzyme-substrate complex can form when the substrate \((\mathrm{s})\) bind (s) to the active site of the enzyme. Which environmental condition might alter the conformation of an enzyme to the extent that its substrate is unable to bind? a. Enzyme \(A\) at \(40^{\circ} \mathrm{C}\) b. Enzyme \(B\) at pH 2 c. Enzyme \(X\) at \(p H 4\) d. Enzyme \(Y\) at \(37^{\circ} \mathrm{C}\)
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