Enzyme Catalysis: Identifying the Non-Applicable Statement
The question asks to identify the statement that does not apply to enzyme-catalyzed reactions. Let's analyze each option:
Applicable Principles in Enzyme Catalysis
- Option 1: Propinquity Effects Enzymes facilitate catalysis by bringing substrate molecules close together (propinquity) and orienting them optimally within the active site. This proximity and orientation significantly increase the reaction rate compared to uncatalyzed reactions in dilute solution. This statement is applicable.
- Option 2: Substrate Strain Upon binding to the enzyme's active site, the substrate often undergoes conformational changes. This binding can induce strain in the substrate's bonds, weakening them and making them more susceptible to breaking, thus lowering the activation energy. This statement is applicable.
- Option 4: Acid-Base Chemistry Many enzymatic reactions involve acid-base catalysis. Amino acid residues in the enzyme's active site, such as aspartate, glutamate, histidine, lysine, or arginine, can act as proton donors (acids) or acceptors (bases) to facilitate the reaction mechanism. This statement is applicable.
Non-Applicable Statement Analysis
- Option 3: Rate of Reverse Reaction Enzymes are highly efficient catalysts that accelerate the rate at which a reaction reaches equilibrium. Importantly, enzymes accelerate the rates of both the forward and reverse reactions. They do not change the equilibrium constant ($K_{eq}$) or the overall thermodynamics ($\Delta G$) of the reaction. Therefore, the statement that enzymes do not accelerate the rate of the reverse reaction is incorrect.
Conclusion
Based on the analysis, the statement that is NOT applicable to enzyme-catalyzed reactions is that enzymes do not accelerate the rate of the reverse reaction.
Important Questions from Enzyme Kinetics and Michaelis Menten Equation
- An enzyme (E) catalyzes the biochemical reaction $A \rightarrow B$ with $k_{cat}$ equal to $500 s^{-1}$. If the initial reaction velocity ($V_0$) is $10 \mu M.s^{-1}$ at the total enzyme concentration $[E_t]$ of 30 nM and substrate concentration $[A]$ of $40 \mu M$, the value of $K_m$ (in $\mu M$) is ________
Within the Michaelis-Menten framework, the ratio of $v_0/V_{max}$
when $[S] = 20 \times K_m$ is _________.
(Round off to two decimal places)
The enzyme $\alpha$-amylase used in starch hydrolysis has an affinity constant ($K_m$) value of $0.005$ M. To achieve one-fourth of the maximum rate of hydrolysis, the required starch concentration in mM (rounded off to two decimal places) is____.
An enzymatic reaction exhibits Michaelis-Menten kinetics. For this reaction, on doubling the concentration of enzyme while maintaining [S] >> [$E_o$],
- In an assay of the type II dehydroquinase of molecular mass 18 kDa, it is found that the $V_{max}$ of the enzyme is $0.0134 \ \mu mol.min^{-1}$ when $1.8 \ \mu g$ enzyme is added to the assay mixture. If the $K_m$ for the substrate is $25 \ \mu M$, the $k_{cat}/K_m$ ratio will be ____________________ $\times 10^4 \ M^{-1}.s^{-1}$.
