Q.55 Given below are two statements:
Statement I: Cooperativity in receptor-ligand interaction causes
large change in receptor activation with small change in ligand concentration.
Statement II: In amplification, the enzyme associated with signal
receptor is activated which in turn activates many downstream enzymes in a so
called enzyme cascade.
In the light of the above statements, choose the correct answer from the options given below:
- Both Statement I and Statement II are true
- Both Statement I and Statement II are false
- Statement I is true but Statement II is false
- Statement I is false but Statement II is true
Both statements are correct descriptions of key signal transduction principles. Cooperativity amplifies sensitivity to ligand changes, while enzyme cascades provide signal amplification in pathways.
Correct Option Explained
Both Statement I and Statement II are true.
Statement I accurately describes cooperativity: In receptors like GPCRs or hemoglobin, binding of one ligand molecule enhances affinity for subsequent ligands (positive cooperativity), yielding a sigmoidal response curve. This allows small ligand concentration changes to trigger large activation shifts, ideal for physiological switches.
Statement II correctly outlines amplification: Receptor-associated enzymes (e.g., receptor tyrosine kinases) activate upon ligand binding, then phosphorylate/activate multiple downstream kinases in cascades (e.g., MAPK/ERK pathway). One activated receptor thus propagates signals exponentially.
Why Other Options Are Incorrect
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Both false: Invalidates verified mechanisms in cell signaling.
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Statement I true, II false: II matches standard cascade amplification (e.g., G-protein cycles).
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Statement I false, II true: I reflects Hill coefficient >1 effects in cooperative binding.
Introduction to Key Concepts
Cooperativity in receptor-ligand interaction enables cells to respond sharply to small ligand concentration changes, while amplification via enzyme cascades boosts weak signals. These mechanisms underpin signaling in molecular biology, vital for GATE Life Sciences questions on cellular processes.
Cooperativity Mechanism
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Positive cooperativity shifts binding curves from hyperbolic to sigmoidal, heightening sensitivity (Hill coefficient n>1).
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Example: Insulin receptor dimerization amplifies activation; one ligand triggers conformational changes for multiple bindings.
Amplification in Cascades
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Receptor enzymes activate downstream kinases (e.g., Ras-Raf-MEK-ERK), where each step activates many substrates.
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In GPCR pathways, one receptor activates hundreds of G-proteins, cascading to amplify signals 10^4-fold.
Mechanism Effect Example Cooperativity Large activation from small [ligand] change Hemoglobin O₂ binding Enzyme Cascade One receptor → many products MAPK pathway in growth signals These integrate in plant hormone signaling (e.g., auxin receptors) or stress responses, aiding biotech applications like PCR-linked studies. Master for genetics and physiology exams.
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