biology : class11 Fructose-6-Phosphate : Location, Steps, Products, ATP Yield : Glycolysis MCQ Questions and Answers
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Fructose-6-Phosphate
MCQ questions and answers.
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MCQ Questions
1. In glycolysis, fructose-6-phosphate is formed from glucose-6-phosphate by which chemically significant transformation?
A.
Oxidation of the C6 hydroxyl group to a carboxyl group
B.
Isomerization of an aldose phosphate into a ketose phosphate
C.
Phosphorylation of the C1 hydroxyl group using ATP
D.
Cleavage of a six-carbon phosphate into two three-carbon phosphates
Correct Answer:
Isomerization of an aldose phosphate into a ketose phosphate
Explanation:
Glucose-6-phosphate, an aldose phosphate, is reversibly converted into fructose-6-phosphate, a ketose phosphate, by phosphoglucose isomerase. The carbon skeleton and phosphate count remain unchanged.
2. Which enzyme directly catalyzes the conversion of glucose-6-phosphate to fructose-6-phosphate during glycolysis?
A.
Phosphofructokinase-1
B.
Hexokinase
C.
Phosphoglucose isomerase
D.
Aldolase
Correct Answer:
Phosphoglucose isomerase
Explanation:
Phosphoglucose isomerase catalyzes the reversible interconversion of glucose-6-phosphate and fructose-6-phosphate. The other enzymes act at different glycolytic steps.
3. The conversion of fructose-6-phosphate to fructose-1,6-bisphosphate requires which combination of enzyme, phosphate donor, and ATP consequence?
A.
Phosphoglucose isomerase, inorganic phosphate, and ATP production
B.
Phosphofructokinase-1, ATP, and consumption of one ATP equivalent
C.
Hexokinase, ATP, and production of one ATP equivalent
D.
Aldolase, ADP, and consumption of one ATP equivalent
Correct Answer:
Phosphofructokinase-1, ATP, and consumption of one ATP equivalent
Explanation:
Phosphofructokinase-1 transfers a phosphate group from ATP to fructose-6-phosphate, producing fructose-1,6-bisphosphate and consuming one ATP molecule.
4. At which carbon atom of fructose-6-phosphate is the second phosphate group added during glycolysis?
A.
C1
B.
C2
C.
C5
D.
C6
Correct Answer:
C1
Explanation:
Fructose-6-phosphate already contains a phosphate at C6. Phosphofructokinase-1 adds the second phosphate at C1, forming fructose-1,6-bisphosphate.
5. A glycolytic intermediate contains one phosphate at C6 and a ketone functional group at C2. Which intermediate is being described?
A.
Glucose-6-phosphate
B.
Fructose-6-phosphate
C.
Fructose-1,6-bisphosphate
D.
Glyceraldehyde-3-phosphate
Correct Answer:
Fructose-6-phosphate
Explanation:
Fructose-6-phosphate is a six-carbon ketose phosphate with its phosphate group at C6. Fructose-1,6-bisphosphate has additional phosphorylation at C1.
6. What is the net ATP effect of the specific glycolytic step in which fructose-6-phosphate is converted to fructose-1,6-bisphosphate?
A.
One ATP is generated by substrate-level phosphorylation
B.
Two ATP are generated because the substrate has six carbons
C.
One ATP is consumed to drive phosphorylation
D.
No ATP is involved because the reaction is an isomerization
Correct Answer:
One ATP is consumed to drive phosphorylation
Explanation:
Phosphorylation of fructose-6-phosphate by phosphofructokinase-1 uses one ATP. This is an energy-investment step, not an ATP-producing step.
7. Why is fructose-6-phosphate phosphorylated at C1 before cleavage in glycolysis?
A.
The added phosphate converts it into a symmetrical bisphosphate that can be cleaved into two three-carbon phosphates
B.
The added phosphate removes the original phosphate from C6
C.
The added phosphate directly produces two ATP molecules
D.
The added phosphate converts the molecule from a ketose into an aldose
Correct Answer:
The added phosphate converts it into a symmetrical bisphosphate that can be cleaved into two three-carbon phosphates
Explanation:
Phosphorylation of fructose-6-phosphate at C1 produces fructose-1,6-bisphosphate, preparing the six-carbon intermediate for aldolase-mediated cleavage into two three-carbon phosphate-containing molecules.
8. Which statement best distinguishes the glycolytic reactions involving glucose-6-phosphate and fructose-6-phosphate?
A.
Glucose-6-phosphate is phosphorylated at C6, whereas fructose-6-phosphate is phosphorylated at C1
B.
Glucose-6-phosphate is oxidized, whereas fructose-6-phosphate is reduced
C.
Glucose-6-phosphate is cleaved, whereas fructose-6-phosphate is condensed
D.
Glucose-6-phosphate produces ATP directly, whereas fructose-6-phosphate does not react with ATP
Correct Answer:
Glucose-6-phosphate is phosphorylated at C6, whereas fructose-6-phosphate is phosphorylated at C1
Explanation:
Glucose-6-phosphate is the product of the first phosphorylation of glucose, while fructose-6-phosphate undergoes phosphorylation at C1 by phosphofructokinase-1 to form fructose-1,6-bisphosphate.
9. If phosphofructokinase-1 is inhibited, which immediate change involving fructose-6-phosphate is most likely in a glycolyzing cell?
A.
Fructose-6-phosphate accumulates because its conversion to fructose-1,6-bisphosphate decreases
B.
Fructose-6-phosphate disappears because it is rapidly cleaved into pyruvate
C.
Fructose-6-phosphate is converted directly into glyceraldehyde-3-phosphate
D.
Fructose-6-phosphate is oxidized to carbon dioxide in the same step
Correct Answer:
Fructose-6-phosphate accumulates because its conversion to fructose-1,6-bisphosphate decreases
Explanation:
Phosphofructokinase-1 catalyzes the ATP-dependent conversion of fructose-6-phosphate to fructose-1,6-bisphosphate. Inhibition of this enzyme reduces consumption of fructose-6-phosphate, favoring its accumulation.
10. Which sequence correctly places fructose-6-phosphate within the early steps of glycolysis?
A.
Glucose → glucose-6-phosphate → fructose-6-phosphate → fructose-1,6-bisphosphate
B.
Glucose → fructose-1,6-bisphosphate → glucose-6-phosphate → fructose-6-phosphate
C.
Glucose → fructose-6-phosphate → glucose-6-phosphate → fructose-1,6-bisphosphate
D.
Glucose → glucose-6-phosphate → fructose-1,6-bisphosphate → fructose-6-phosphate
Explanation:
In glycolysis, glucose is first phosphorylated to glucose-6-phosphate, which is isomerized to fructose-6-phosphate. The latter is then phosphorylated at C1 to form fructose-1,6-bisphosphate.
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