Allosteric regulation Knowledge-Based Download PDF

Questions

1. 1.

   Which of the following describes how feedback inhibition regulates a multi-step metabolic pathway through allosteric control?

   • A) The final product of the pathway binds to an allosteric site on the first enzyme, inducing a conformational change that decreases its activity.
   • B) The initial substrate binds covalently to the active site of the terminal enzyme, permanently denaturing its tertiary structure.
   • C) An intermediate metabolite competes directly with the starting substrate for the active site of every enzyme in the sequence.
   • D) The final product alters the primary amino acid sequence of the regulatory enzyme to permanently block transcription.
2. 2.

   Which of the following best distinguishes an enzyme's allosteric site from its active site?

   • A) The allosteric site forms covalent bonds with intermediate products during the reaction cycle, whereas the active site relies solely on hydrogen bonding.
   • B) The allosteric site directly provides the activation energy needed for catalysis, whereas the active site only stabilizes the final products.
   • C) The allosteric site binds regulatory effector molecules at a distinct physical location to alter enzyme activity, whereas the active site binds substrates to catalyze the chemical reaction.
   • D) The allosteric site is only present on monomeric enzymes in the cytoplasm, whereas the active site is restricted to multi-subunit membrane-bound complexes.
3. 3.

   Which of the following statements correctly describes how an allosteric activator enhances the catalytic activity of an enzyme?

   • A) It binds to a specific regulatory site distinct from the active site, stabilizing the enzyme in its active conformation with high substrate affinity.
   • B) It binds directly to the active site, competing with inhibitory molecules to maintain substrate access.
   • C) It forms a permanent covalent bond with amino acid residues in the catalytic pocket to lower the activation energy.
   • D) It acts as a cofactor that undergoes irreversible cleavage to convert an inactive zymogen into a functional enzyme.
4. 4.

   Which of the following statements best describes the mechanism of cooperativity in allosteric enzymes?

   • A) A competitive inhibitor binds directly to the active site, thereby preventing substrate attachment at adjacent subunits.
   • B) The binding of a substrate molecule to one active site stabilizes the catalytically active conformation in all other subunits.
   • C) An end-product molecule irreversibly breaks disulfide linkages between regulatory subunits to alter enzyme shape.
   • D) A non-protein cofactor forms a permanent covalent bond with the catalytic site to stimulate enzymatic activity.
5. 5.

   Which statement accurately describes how an allosteric inhibitor affects enzyme function?

   • A) It binds to a regulatory site distinct from the active site, inducing a conformational change that reduces the enzyme's activity.
   • B) It binds directly to the active site in competition with the substrate, blocking substrate access without altering enzyme shape.
   • C) It forms an irreversible covalent bond within the active site, permanently denaturing the enzyme's primary structure.
   • D) It functions as a coenzyme that is chemically consumed during the catalytic cycle to convert the substrate into an inhibitor.