Q. 29 Which one of the following profiles represent the phenomenon of cooperativity?
Which Profile Represents the Phenomenon of Cooperativity?
Question Overview
The following velocity (v) versus substrate concentration ([S]) profiles are given.
Question:
Which of the following profiles represents the phenomenon of cooperativity?
Options:
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(A)
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(B)
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(C)
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(D)
What Is Cooperativity in Enzyme Kinetics?
Cooperativity is observed in multisubunit enzymes where the binding of a substrate molecule to one active site affects the binding affinity of substrate molecules at other active sites.
Key Characteristics of Cooperative Enzymes
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Do not follow Michaelis–Menten kinetics
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Show a sigmoidal (S-shaped) v vs [S] curve
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Common example: Hemoglobin (positive cooperativity)
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Described by the Hill equation, not Michaelis–Menten equation
Identifying Cooperativity from a Graph
| Curve Type | Interpretation |
|---|---|
| Hyperbolic | Michaelis–Menten (non-cooperative) |
| Sigmoidal (S-shaped) | Cooperative binding |
| Bell-shaped | Substrate inhibition |
| Irregular / multi-step | Complex or mixed kinetics |
Analysis of the Given Options
Option (A) — Incorrect ❌
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Curve is hyperbolic
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Typical of Michaelis–Menten enzymes
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Indicates non-cooperative binding
👉 Not cooperativity
Option (B) — Incorrect ❌
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Shows an initial rise followed by a decline
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Represents substrate inhibition
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High substrate concentration reduces velocity
👉 Not cooperativity
Option (C) — Correct ✅
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Shows a sigmoidal (S-shaped) curve
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Velocity increases slowly at low [S], then rapidly, then plateaus
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Classic signature of positive cooperativity
👉 This profile represents cooperativity
Option (D) — Incorrect ❌
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Shows irregular or biphasic behavior
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May indicate multiple enzyme systems or regulatory effects
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Not a smooth sigmoidal curve
👉 Not a standard cooperative profile
Correct Answer
✅ (C)
The sigmoidal velocity–substrate curve in option (C) clearly represents the phenomenon of cooperativity.
Why Option (C) Is Correct
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Cooperative enzymes require initial substrate binding to enhance further binding
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This produces a slow start, followed by a steep increase, then saturation
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Only sigmoidal curves indicate cooperative interactions
Final Conclusion
Among the given velocity versus substrate concentration profiles, option (C) shows a sigmoidal curve, which is the hallmark of cooperativity in enzyme kinetics.
