Q.34 In hypothetical enzymatic reaction
A ——(enzyme 1)——> B
——(enzyme 2)——> C
The end product C is allosteric inhibitor of Enzyme 1.
C will also regulate the activity of Enzyme 1 by
- competitive inhibition
- feedback inhibition
- irreversible inhibition
- competitive inhibition and irreversible inhibition both
In the given enzymatic pathway (A → B → C), where end product C acts as an allosteric inhibitor of enzyme 1, this exemplifies a classic regulatory mechanism to prevent overproduction.
Correct Answer
feedback inhibition
C binds to an allosteric site (distinct from the active site) on enzyme 1, inducing a conformational change that reduces its activity, thereby slowing the pathway when C accumulates—this is textbook feedback inhibition.
Option Analysis
Competitive Inhibition
Competitive inhibitors bind the active site, directly competing with substrate A; C as an allosteric inhibitor targets a separate regulatory site, so this doesn’t apply.
Feedback Inhibition
Correct: End-product inhibition of an early enzyme via allostery is the definition of feedback (or end-product) inhibition, common in biosynthetic pathways like amino acid synthesis.
Irreversible Inhibition
Irreversible inhibitors covalently modify the enzyme, permanently disabling it (e.g., aspirin on COX); allosteric feedback is reversible, allowing dynamic regulation.
Competitive and Irreversible Both
Incorrect combination: Neither competitive (site mismatch) nor irreversible (reversible nature) fits; it’s purely allosteric feedback.
Option Mechanism Site Reversibility Matches Scenario? Competitive Inhibition Active site Reversible No Feedback Inhibition Allosteric site Reversible Yes Irreversible Inhibition Covalent/active Permanent No Both Competitive & Irreversible Mixed Mixed No Clinical Relevance
Feedback inhibition ensures metabolic efficiency, key for exams like NEET/CSIR; disruptions (e.g., in metabolic disorders) lead to toxic buildup.
