MCAT® ExamBiological and Biochemical Foundations of Living SystemsMedium
A research team is investigating a novel protein that acts as a transcription factor. They discover that its activity is significantly increased when it binds to a specific small molecule. This small molecule does not directly interact with the DNA, but instead induces a conformational change in the protein that enhances its DNA-binding affinity. Which regulatory mechanism best describes the action of this small molecule?
- AFeedback inhibition
- BAllosteric regulation
- CCompetitive inhibition
- DCovalent modification
Show answer & explanationAnswer & explanation
Correct answer: B. Allosteric regulation
Allosteric regulation involves a molecule binding to a site on a protein distinct from the active site (or DNA-binding site in this case), causing a conformational change that alters the protein's activity. This description perfectly matches the scenario.
Why the other options are wrong
- A. Feedback inhibition is a regulatory mechanism where the end product of a pathway inhibits an enzyme earlier in the pathway, which is not the scenario presented.
- C. Competitive inhibition involves a molecule binding to the active site, directly competing with the substrate, which is not described here.
- D. Covalent modification involves the addition or removal of a chemical group (e.g., phosphorylation), which is not stated to be occurring.
Allosteric Regulation
Regulation of an enzyme or other protein by binding an effector molecule at a site other than the protein's active site (or DNA-binding site), causing a conformational change that affects its activity.
- Effector binds to an allosteric site, not the active site.
- Induces a conformational change in the protein.
- Can either activate or inhibit protein function.
- Common in enzyme regulation and transcription factors.
Memory trick: Allosteric Alligator: bites a different spot, changes the whole protein's mood.