Glycolysis control — Which statements describe how ATP and ADP regulate the glycolytic pathway?
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AAllosteric stimulation by ADP
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BAllosteric inhibition by ATP
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CFeedback (product) inhibition by ATP at key control steps
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DAll of the above
Answer
Correct Answer: All of the above
Explanation
Introduction / Context:Glycolytic flux is tightly regulated to balance cellular energy status. Adenine nucleotides act as key signals: ATP indicates high energy charge and suppresses glycolysis, whereas ADP/AMP indicate low energy and stimulate it.
Given Data / Assumptions:
- Phosphofructokinase-1 (PFK-1) is a major control point.
- ATP and citrate inhibit, while ADP/AMP and fructose-2,6-bisphosphate activate.
- We evaluate multiple statements about regulation.
Concept / Approach:ATP binds allosteric sites on PFK-1 to decrease affinity for fructose-6-phosphate, reducing flux when energy is sufficient. ADP/AMP relieve this inhibition, enhancing glycolysis when energy is low. ATP also acts as a product and end-goal of the pathway, constituting feedback inhibition at several nodes, including pyruvate kinase regulation in some tissues.
Step-by-Step Solution:
Confirm ADP effect: ADP/AMP are classic allosteric activators of PFK-1.Confirm ATP effect: ATP is an allosteric inhibitor of PFK-1 and can inhibit pyruvate kinase in some contexts.Recognize feedback logic: accumulation of ATP signals to slow further ATP production.Therefore, all statements are correct.Verification / Alternative check:In vitro PFK-1 kinetics demonstrate sigmoidal curves shifted by ATP and ADP/AMP, validating the regulatory scheme.
Why Other Options Are Wrong:
- Selecting only one statement ignores the integrated control by both ATP and ADP.
Common Pitfalls:Confusing ATP’s dual roles: substrate for kinases and allosteric inhibitor at high concentrations. The allosteric site is distinct from the catalytic site.
Final Answer:All of the above