Q42. Given below are four plots obtained from separate experiments on enzyme
inhibition kinetics. The velocity (v) of the reaction is plotted at varying
concentrations of substrate (s) and inhibitor (I). The plot(s) corresponding to
competitive inhibition is/are
(A) (i)
(B) (ii)
(C) (iii)
(D) (iv)
Competitive inhibition in enzyme kinetics is identified by specific patterns in Lineweaver-Burk plots where lines intersect at the y-axis. Without the actual plots for Q42, the correct option depends on recognizing the hallmark: same Vmax (y-intercept) but increased Km (x-intercept shifts right). This matches competitive inhibition across CSIR NET-style questions.
Competitive Inhibition Traits
Competitive inhibitors bind the enzyme’s active site, competing directly with substrate and raising apparent Km while leaving Vmax unchanged. In Michaelis-Menten plots, curves shift right but reach the same maximum velocity at high substrate levels. Lineweaver-Burk plots (1/v vs 1/[S]) show lines with the same y-intercept (1/Vmax) but steeper slopes and more positive x-intercepts (-1/Km).
Other Inhibition Patterns
Non-competitive inhibition lowers Vmax (higher y-intercept) but keeps Km unchanged (same x-intercept). Uncompetitive inhibition produces parallel lines with decreased Vmax and Km. Mixed inhibition alters both intercepts without y-axis intersection.
Evaluating Q42 Options
- (i): Likely competitive if lines intersect on y-axis (same Vmax, varying Km).
- (ii): Probably non-competitive if lines intersect on x-axis.
- (iii): Could be uncompetitive with parallel lines.
- (iv): Might show mixed inhibition or no clear pattern.
The answer is the option matching competitive traits: y-intercept convergence.
Introduction to Enzyme Inhibition Kinetics Plots
Enzyme inhibition kinetics plots reveal how inhibitors affect enzyme activity, crucial for CSIR NET enzyme inhibition kinetics preparation. Competitive inhibition occurs when inhibitors mimic substrates, binding the active site and increasing apparent Km while Vmax remains unchanged. Lineweaver-Burk plots (double reciprocal: 1/v vs 1/[S]) are key for identification in exams like CSIR NET Q42.
Key Characteristics of Competitive Inhibition
In competitive enzyme inhibition plots, high substrate overcomes inhibition by outcompeting the inhibitor.
- Michaelis-Menten: Hyperbola shifts right, same Vmax
- Lineweaver-Burk: Lines intersect at y-axis (1/Vmax same), x-intercept shifts right (-1/Km more positive), steeper slopes
Equation: v = Vmax[S] / (Km(1 + [I]/Ki) + [S])
Comparison of Inhibition Types
| Inhibition Type | Km Effect | Vmax Effect | Lineweaver-Burk Pattern | CSIR NET Relevance |
|---|---|---|---|---|
| Competitive | ↑ | Unchanged | Y-axis intersection | Q42 plot identification |
| Non-competitive | Unchanged | ↓ | X-axis intersection | Vmax reduction questions |
| Uncompetitive | ↓ | ↓ | Parallel lines | Rare, parallel slope |
| Mixed | ↑ or ↓ | ↓ | Different intercepts | Advanced kinetics |
Solving CSIR NET Q42: Step-by-Step
For enzyme inhibition kinetics plots competitive inhibition questions:
- Confirm plot type (likely Lineweaver-Burk for CSIR NET).
- Check y-intercepts: Same = competitive (unchanged Vmax).
- Verify x-intercepts: Varying/more positive = increased Km.
- Eliminate others: X-intercept same (non-competitive), parallel (uncompetitive).
Answer: Option showing y-axis intersection (typically (i) or specified).
CSIR NET Preparation Tips
- Practice CSIR NET enzyme inhibition plots from past papers focusing on graph interpretation.
- Calculate Km app = Km(1 + [I]/Ki) for competitive cases.
- Use mock tests to spot patterns quickly under time pressure.
