Q55.Allosterically regulated enzymes are:
(1) Oligomeric proteins
(2) Possess regulatory and catalytic domains
(3) Shows sigmoidal behavior
(4) Both 2 and 3
Allosterically regulated enzymes are defined by their unique structural and kinetic properties that enable feedback control in metabolic pathways. The correct answer is option (4): Both 2 and 3.
Correct Answer
Option (4) Both 2 and 3 – Allosterically regulated enzymes possess regulatory and catalytic domains, and they show sigmoidal behavior.
Option Analysis
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(1) Oligomeric proteins: True but incomplete. Most allosteric enzymes are oligomeric (multi-subunit), allowing cooperativity where binding at one site affects others, but this alone doesn’t define them—all oligomeric proteins aren’t allosteric.
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(2) Possess regulatory and catalytic domains: Correct. They have distinct catalytic sites for substrates and allosteric (regulatory) sites for effectors like activators or inhibitors, enabling conformational changes.
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(3) Shows sigmoidal behavior: Correct. Unlike Michaelis-Menten hyperbolic kinetics, they display sigmoidal substrate-velocity curves due to cooperative binding, allowing sensitive regulation.
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(4) Both 2 and 3: Best answer, as it captures the core defining features without overgeneralizing oligomeric structure.
Introduction to Allosteric Regulation
Master allosterically regulated enzymes characteristics for NEET and life sciences exams. These enzymes control metabolism via effectors binding at non-active sites, shifting from tense (T, low activity) to relaxed (R, high activity) states for precise cellular feedback.
Key Structural Features
Allosteric enzymes are typically oligomeric proteins with multiple subunits.
Each subunit has catalytic domains for substrate binding and separate regulatory domains for allosteric effectors.
This setup enables positive (activators) or negative (inhibitors) regulation, like in phosphofructokinase-1.
Kinetic Behavior
They exhibit sigmoidal kinetics due to cooperativity, not hyperbolic Michaelis-Menten curves.
Low substrate favors T-state; high substrate shifts to R-state, amplifying response.
Examples: Hemoglobin (O2 binding), aspartate transcarbamoylase.
Exam Relevance
Options 2 and 3 highlight regulatory domains and sigmoidal behavior as hallmarks. Focus on models like MWC (concerted) for T-R shifts in competitive prep.
