Question

Assertion: Allosteric enzymes show feedback inhibition.
Reason: The inhibitor is competitive.
(a) Both Assertion and Reason are correct and Reason is the correct explanation of Assertion.
(b) Both Assertion and Reason are correct, but Reason is not the correct explanation of Assertion.
(c) Assertion is correct but Reason is incorrect.
(d) Both the Assertion and Reason are incorrect.

Answer 1

Hint: Via reversible, noncovalent binding of a regulatory metabolite called a modulator, allosteric enzymes act. Allosteric regulation is just any form of regulation where the regulatory molecule (an activator or inhibitor) binds to an enzyme other than the active site somewhere.

Complete answer:
-The position where the regulator binds is called the allosteric site.
-The regulatory enzyme is directly inhibited by the end product of the pathway in certain multienzyme systems if the end product rises in excess of the cell's needs.
-All subsequent enzymes work at reduced rates when the regulatory enzyme reaction is slowed since their substrates are exhausted by mass action.
-The rate of development of the end product of the pathway is thus brought into line with the needs of the cell.
-This form of control is called the inhibition of feedback. It is not competitive with inhibitors.
-Usually, inhibition of feedback acts at the first committed stage of the pathway, which means the first step that is essentially irreversible.
-For example, The ATP molecule of the energy carrier is an allosteric inhibitor of some of the enzymes involved in cellular respiration, a mechanism that makes cellular reactions power ATP. This feedback inhibition prevents more ATP from being produced when there is a lot of ATP. This is useful since ATP is a molecule that is unstable. Much of it could go to waste if too much ATP were generated, spontaneously breaking back into its components (ADP and Pi).
So, the correct answer is ‘Assertion is correct but Reason is incorrect’.

Note: Typically, allosteric enzymes have several active sites located on different subunits of proteins. When an allosteric inhibitor binds to an enzyme, it slightly changes all the active sites on the protein subunits so that they work less well.