Q41. Match the parameters in Group 1 with the correct options in Group 2
| Group 1 | Group 2 |
|---|---|
| P. Km Q. kcat/Km R. pKa S. Ki | 1. Catalytic efficiency of the enzyme 2. Affinity of enzyme to the inhibitor 3. Affinity of enzyme to the substrate 4. Maximum buffering capacity |
Correct Answer: (B) P-3, Q-1, R-4, S-2
Km reflects enzyme-substrate affinity, with lower values indicating stronger binding. kcat/Km measures catalytic efficiency, combining turnover rate and substrate affinity. pKa relates to buffering capacity, peaking at maximum proton donation/acceptance. Ki indicates inhibitor affinity, where lower values mean tighter binding.
Parameter Matching
-
P. Km → 3. Affinity of enzyme to the substrate: Km is the substrate concentration at half Vmax; high Km means low affinity as more substrate is needed.
-
Q. kcat/Km → 1. Catalytic efficiency of the enzyme: This ratio shows how effectively enzymes convert substrate to product, especially at low concentrations.
-
R. pKa → 4. Maximum buffering capacity: Buffers resist pH change best at their pKa, providing peak capacity there.
-
S. Ki → 2. Affinity of enzyme to the inhibitor: Lower Ki values denote higher inhibitor binding strength, similar to Km for substrates.
Option Analysis
| Option | P (Km) | Q (kcat/Km) | R (pKa) | S (Ki) | Correct? | Reason |
|---|---|---|---|---|---|---|
| (A) | 3 | 1 | 2 | 4 | No | R wrongly matches inhibitor affinity; pKa is buffering. |
| (B) | 3 | 1 | 4 | 2 | Yes | All match: substrate affinity, efficiency, buffering, inhibitor affinity. |
| (C) | 1 | 2 | 4 | 3 | No | P confuses Km with efficiency; Q mismatches inhibitor. |
| (D) | 1 | 4 | 2 | 3 | No | Multiple errors: Km not efficiency, kcat/Km not buffering. |
Introduction to Enzyme Kinetics Parameters Matching
Enzyme kinetics parameters matching like Km, kcat/Km, pKa, and Ki is crucial for GATE Life Sciences aspirants tackling biochemistry MCQs. This guide solves a classic PYQ on matching these terms to their definitions—substrate affinity, catalytic efficiency, buffering capacity, and inhibitor affinity—helping students ace competitive exams.
Understanding Km: Enzyme-Substrate Affinity
Km, or Michaelis constant, measures enzyme affinity for substrate. Lower Km signals higher affinity, as less substrate reaches half Vmax. In kinetics, it’s key for plotting Michaelis-Menten curves.
kcat/Km: Measure of Catalytic Efficiency
kcat/Km, the specificity constant, gauges catalytic efficiency. It reflects turnover (kcat) normalized by Km, ideal for low-substrate conditions in vivo. High values mean superior performance.
pKa and Maximum Buffering Capacity
pKa denotes the pH where acids/bases half-dissociate, yielding maximum buffering capacity. Enzymes and buffers optimize here to stabilize pH in reactions.
Ki: Enzyme-Inhibitor Affinity
Ki is the inhibition constant; low Ki indicates strong inhibitor binding, akin to Km but for competitive/non-competitive inhibitors in drug design.
GATE Exam Tips
Practice matching enzyme kinetics parameters matching Km kcat/Km for quick scoring. Use Lineweaver-Burk plots to visualize differences.
