The binding efficiency of three different receptorsR1, R2 and R3 were tested against a ligand using
equilibrium dialysis, with a constant concentration of receptor and varying concentrations of ligand. The
Scatchard plot of receptor titration with different concentration of ligand is given below
(ris moles of bound ligand per moles of receptor and c is concentration of free ligand)
Q.51 Which one of the receptors has thehighestaffinity for the ligand?
(A) R1 (B) R2 (C) R3 (D) R4
📘 Key Concept
In a Scatchard plot:
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Slope = −1/Kd
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Steeper slope = lower Kd = higher affinity
✅ Correct Answer
(A) R1
🧠 Explanation
From the plot:
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R1 has the steepest downward slope
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A steeper slope indicates:
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Smaller dissociation constant (Kd)
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Stronger ligand binding
-
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Therefore, R1 has the highest ligand affinity
❌ Option-wise Explanation
| Option | Explanation |
|---|---|
| A) R1 | ✅ Steepest slope → highest affinity |
| B) R2 | Less steep than R1 |
| C) R3 | Moderate slope |
| D) R4 | Least steep → lowest affinity |
🔍 Final Conclusion
The receptor with the highest affinity for the ligand is R1, making Option A correct.
