Q.5 In the feedback regulation of an enzyme, the end product binds to the
(A) active site of the enzyme.
(B) allosteric site of the enzyme.
(C) enzyme-substrate complex.
(D) substrate.
The correct answer is (B) allosteric site of the enzyme. In feedback regulation, typically feedback inhibition, the end product of a metabolic pathway binds to an allosteric site on the enzyme catalyzing an early step, inducing a conformational change that inhibits activity and prevents overproduction.
Option Analysis
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(A) Active site: Incorrect, as the active site binds substrates for catalysis; end products in feedback inhibition bind elsewhere to avoid competing directly with substrates.
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(B) Allosteric site: Correct, as this regulatory site, distinct from the active site, allows the end product to alter enzyme shape and reduce activity without blocking substrate binding.
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(C) Enzyme-substrate complex: Incorrect, since binding occurs on the free enzyme, not the complex, to preemptively halt the pathway.
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(D) Substrate: Incorrect, as substrates initiate reactions; end products regulate via non-competitive inhibition at allosteric sites.
Introduction to Feedback Regulation
Feedback regulation of enzyme end product allosteric site controls metabolic pathways by preventing excess product buildup. This mechanism, vital for cellular homeostasis, involves the pathway’s final product inhibiting an early enzyme, ensuring efficient resource use in biochemistry.
Mechanism Explained
In feedback inhibition—a key feedback regulation of enzyme end product allosteric site process—the end product binds non-competitively to the allosteric site. This binding induces a conformational shift, deforming the active site and reducing catalytic efficiency. As product levels drop, inhibition reverses, reactivating the enzyme.
Why Not Other Sites?
Active site binding would mimic competitive inhibition by substrates, not regulation. Enzyme-substrate complexes form post-binding, missing the preventive role. Substrates promote, not inhibit, activity.
Biological Significance
This regulation appears in amino acid synthesis, like threonine deaminase inhibited by isoleucine. It conserves energy, maintains balance, and links to CSIR NET topics in enzyme kinetics and metabolic control.
