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
- The catalytic efficiency of an enzyme following Michaelis-Menten kinetics is defined by
You are characterizing a new enzyme isolated and purified in the laboratory. If the maximum velocity of the enzyme is $1800 \text{ } \mu moles \text{ L}^{-1} \text{min}^{-1}$ and the total concentration of the enzyme in the reaction mixture is $1.5 \mu \text{M}$, then the turnover number of the enzyme is _______ $\text{s}^{-1}$. (answer in integer)
You have purified an enzyme using a series of chromatographic methods. It was observed that a $10 \mu \text{ g mL}^{-1}$ of this purified enzyme converted $10 \text{ mM}$ substrate per hour at 25$^{\circ}$C and pH 7. Its specific activity is _______ $\text{IU } \mu\text{g}^{-1}$. (rounded off to three decimal places)
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 activity of lactate dehydrogenase can be measured by monitoring the following reaction:
Pyruvate + NADH $ \longrightarrow $ Lactate + $NAD^+$
The molar extinction coefficient of NADH at 340 nm is $6220 \ M^{-1}.cm^{-1}$. $NAD^+$ does not absorb at this wavelength. In an assay, $25 \ \mu L$ of a sample of enzyme (containing $5 \ \mu g$ protein per mL) was added to a mixture of pyruvate and NADH to give a total volume of 3 mL in a cuvette of 1 cm pathlength. The rate of decrease in absorbance at 340 nm was $0.14 \ min^{-1}$. The specific activity of the enzyme will be ____________________ $ \mu mol.min^{-1}.mg^{-1}$.
