biology : class11 Phosphofructokinase Regulation : Location, Steps, Products, ATP Yield : Glycolysis MCQ Questions and Answers
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Phosphofructokinase Regulation
MCQ questions and answers.
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MCQ Questions
1. Which combination most strongly activates phosphofructokinase-1 (PFK-1) in a liver cell under low-energy conditions?
A.
High ATP and high citrate
B.
High AMP and high fructose-2,6-bisphosphate
C.
High citrate and low AMP
D.
High ATP and low fructose-2,6-bisphosphate
Correct Answer:
High AMP and high fructose-2,6-bisphosphate
Explanation:
AMP signals a low-energy state and fructose-2,6-bisphosphate is a powerful activator of PFK-1. Together they increase PFK-1 activity and promote glycolytic flux.
2. A rise in cellular ATP inhibits PFK-1 even when fructose-6-phosphate is abundant. What is the most direct consequence of this inhibition?
A.
Increased conversion of fructose-6-phosphate to fructose-1,6-bisphosphate
B.
Reduced glycolytic commitment at the PFK-1-catalyzed step
C.
Activation of phosphofructokinase-2 and immediate glycolytic acceleration
D.
Increased formation of fructose-2,6-bisphosphate by PFK-1
Correct Answer:
Reduced glycolytic commitment at the PFK-1-catalyzed step
Explanation:
PFK-1 catalyzes the major regulated commitment step of glycolysis. High ATP lowers its activity, reducing formation of fructose-1,6-bisphosphate and slowing glycolytic flux.
3. Why can citrate inhibit PFK-1 even though citrate is not a substrate of the PFK-1 reaction?
A.
Citrate acts as an allosteric signal that indicates abundant biosynthetic and energy resources
B.
Citrate covalently phosphorylates PFK-1 and permanently inactivates it
C.
Citrate is converted directly into fructose-2,6-bisphosphate
D.
Citrate removes AMP from the cytosol by irreversible binding
Correct Answer:
Citrate acts as an allosteric signal that indicates abundant biosynthetic and energy resources
Explanation:
Citrate is an allosteric inhibitor of PFK-1. Its accumulation indicates that mitochondrial metabolism and precursor availability are high, so further glycolytic carbon entry is restrained.
4. In a liver cell, glucagon signaling lowers fructose-2,6-bisphosphate concentration. Which regulatory effect should result?
A.
PFK-1 activity decreases, reducing glycolytic flux
B.
PFK-1 activity increases because fructose-2,6-bisphosphate is inhibitory
C.
PFK-1 becomes independent of ATP inhibition
D.
PFK-1 directly produces more fructose-2,6-bisphosphate
Explanation:
Fructose-2,6-bisphosphate activates PFK-1. Therefore, its glucagon-associated decrease removes an important stimulatory signal and suppresses glycolysis in liver cells.
5. Which change would best counteract the inhibitory effect of ATP on PFK-1?
A.
A decrease in AMP concentration
B.
An increase in citrate concentration
C.
An increase in fructose-2,6-bisphosphate concentration
D.
A decrease in fructose-6-phosphate concentration
Correct Answer:
An increase in fructose-2,6-bisphosphate concentration
Explanation:
Fructose-2,6-bisphosphate strongly activates PFK-1 and can oppose inhibitory influences such as high ATP, thereby favoring the glycolytic reaction catalyzed by PFK-1.
6. A mutation prevents AMP from binding to its regulatory site on PFK-1 but does not affect the catalytic site. Under ATP-depleted conditions, what is most likely to occur?
A.
PFK-1 will be unable to bind fructose-6-phosphate
B.
PFK-1 will fail to receive AMP-mediated activation and glycolysis will be less responsive to low energy
C.
PFK-1 will be permanently activated by ATP
D.
PFK-1 will convert fructose-1,6-bisphosphate back to fructose-6-phosphate
Correct Answer:
PFK-1 will fail to receive AMP-mediated activation and glycolysis will be less responsive to low energy
Explanation:
AMP is an allosteric activator of PFK-1 during energy deficiency. Loss of AMP binding would impair this regulatory response while leaving the catalytic substrate-binding function conceptually distinct.
7. Which pattern of metabolite concentrations would predict the lowest PFK-1 activity in a typical cell?
A.
Low ATP, high AMP, and high fructose-2,6-bisphosphate
B.
High ATP, high citrate, and low AMP
C.
Low citrate, high AMP, and high fructose-2,6-bisphosphate
D.
High fructose-2,6-bisphosphate, low ATP, and high AMP
Correct Answer:
High ATP, high citrate, and low AMP
Explanation:
ATP and citrate inhibit PFK-1, whereas AMP activates it. Thus, high concentrations of both inhibitors together with low AMP produce the strongest inhibitory regulatory environment.
8. A cell has a high ATP-to-ADP ratio but also a high AMP concentration. Which statement best describes PFK-1 regulation?
A.
ATP inhibition is possible, but AMP can oppose it through allosteric activation
B.
AMP is converted into ATP by PFK-1 to remove inhibition
C.
High AMP always inhibits PFK-1 regardless of ATP concentration
D.
PFK-1 is regulated only by fructose-6-phosphate and cannot respond to adenine nucleotides
Correct Answer:
ATP inhibition is possible, but AMP can oppose it through allosteric activation
Explanation:
ATP and AMP exert opposing allosteric effects on PFK-1. The final activity depends on their relative regulatory influences rather than on either metabolite acting alone.
9. If fructose-2,6-bisphosphate synthesis is reduced while ATP and citrate remain low, what is the most likely effect on PFK-1?
A.
PFK-1 activity will be lower than it would be with normal fructose-2,6-bisphosphate levels
B.
PFK-1 activity will increase because fructose-2,6-bisphosphate inhibits the enzyme
C.
PFK-1 will lose its ability to bind fructose-6-phosphate completely
D.
PFK-1 will be activated directly by citrate
Correct Answer:
PFK-1 activity will be lower than it would be with normal fructose-2,6-bisphosphate levels
Explanation:
Even when ATP and citrate do not strongly inhibit PFK-1, reduced fructose-2,6-bisphosphate removes a major positive regulator, decreasing PFK-1 activation and glycolytic flux.
10. Why is PFK-1 regulation considered an effective way to control glycolytic flux rather than merely one isolated reaction?
A.
PFK-1 catalyzes a highly regulated step that commits fructose-6-phosphate toward glycolytic breakdown
B.
PFK-1 is the only enzyme in glycolysis that binds ATP
C.
PFK-1 functions exclusively in the mitochondrion and controls the citric acid cycle directly
D.
PFK-1 produces citrate, which then activates every glycolytic enzyme
Correct Answer:
PFK-1 catalyzes a highly regulated step that commits fructose-6-phosphate toward glycolytic breakdown
Explanation:
PFK-1 controls conversion of fructose-6-phosphate to fructose-1,6-bisphosphate, a key committed step. Its sensitivity to ATP, AMP, citrate, and fructose-2,6-bisphosphate allows cellular energy status to regulate overall glycolytic flux.
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