biology : class11 Fructose-1,6-Bisphosphate : Location, Steps, Products, ATP Yield : Glycolysis MCQ Questions and Answers
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Fructose-1,6-Bisphosphate
MCQ questions and answers.
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MCQ Questions
1. In glycolysis, fructose-1,6-bisphosphate is cleaved by aldolase into which pair of three-carbon products?
A.
Glyceraldehyde-3-phosphate and dihydroxyacetone phosphate
B.
Glyceraldehyde-3-phosphate and 3-phosphoglycerate
C.
Dihydroxyacetone phosphate and phosphoenolpyruvate
D.
3-Phosphoglycerate and phosphoenolpyruvate
Correct Answer:
Glyceraldehyde-3-phosphate and dihydroxyacetone phosphate
Explanation:
Aldolase splits the six-carbon fructose-1,6-bisphosphate molecule between its third and fourth carbon atoms, producing the two three-carbon triose phosphates glyceraldehyde-3-phosphate and dihydroxyacetone phosphate.
2. Which structural feature of fructose-1,6-bisphosphate allows aldolase to generate two three-carbon phosphorylated molecules?
A.
Phosphate groups are attached at carbons 1 and 6, permitting cleavage between carbons 3 and 4
B.
Phosphate groups are attached at carbons 2 and 5, permitting cleavage between carbons 1 and 6
C.
Both phosphate groups are attached to the same carbon, permitting cleavage of the carbon chain
D.
A phosphate group is attached to carbon 3, permitting cleavage between carbons 1 and 2
Correct Answer:
Phosphate groups are attached at carbons 1 and 6, permitting cleavage between carbons 3 and 4
Explanation:
Fructose-1,6-bisphosphate contains phosphate groups at carbon 1 and carbon 6. Aldolase cleaves the central carbon-carbon bond between carbons 3 and 4, yielding two phosphorylated three-carbon products.
3. Why is fructose-1,6-bisphosphate considered a key branch-point intermediate in the sequence of glycolysis reactions?
A.
Its cleavage produces two triose phosphates, allowing the later reactions to proceed twice per original glucose molecule
B.
Its formation directly produces two ATP molecules from one glucose molecule
C.
Its cleavage releases carbon dioxide and completes glucose oxidation
D.
Its conversion directly regenerates NAD+ before any three-carbon reactions occur
Correct Answer:
Its cleavage produces two triose phosphates, allowing the later reactions to proceed twice per original glucose molecule
Explanation:
The six-carbon fructose-1,6-bisphosphate molecule is divided into two three-carbon phosphate-containing molecules. Consequently, each subsequent glycolytic step involving these trioses occurs twice for every original glucose molecule.
4. A glycolytic reaction produces fructose-1,6-bisphosphate from fructose-6-phosphate. Which description correctly identifies the transformation?
A.
Addition of a phosphate group at carbon 1 using ATP
B.
Removal of a phosphate group from carbon 6 using ADP
C.
Oxidation of carbon 1 with simultaneous reduction of NAD+
D.
Cleavage of the six-carbon sugar into two phosphorylated trioses
Correct Answer:
Addition of a phosphate group at carbon 1 using ATP
Explanation:
Phosphofructokinase-1 transfers a phosphate group from ATP to carbon 1 of fructose-6-phosphate, forming fructose-1,6-bisphosphate. The pre-existing phosphate remains at carbon 6.
5. If aldolase acts on one molecule of fructose-1,6-bisphosphate, how many phosphate groups are present in the two products taken together?
A.
Two, with one phosphate group on each product
B.
One, because one phosphate group is removed during cleavage
C.
Three, because an additional phosphate is transferred from ATP
D.
Four, because each product receives both original phosphate groups
Correct Answer:
Two, with one phosphate group on each product
Explanation:
Fructose-1,6-bisphosphate contains two phosphate groups. Aldolase rearranges neither phosphate nor adds or removes one; cleavage distributes one phosphate-containing portion to each three-carbon product.
6. Which pairing correctly matches each product of fructose-1,6-bisphosphate cleavage with its immediate glycolytic fate?
A.
Dihydroxyacetone phosphate is converted into glyceraldehyde-3-phosphate, while glyceraldehyde-3-phosphate continues directly
B.
Glyceraldehyde-3-phosphate is converted into dihydroxyacetone phosphate, while dihydroxyacetone phosphate exits glycolysis
C.
Both products are converted directly into pyruvate without any intermediate reaction
D.
Both products are converted into fructose-6-phosphate before glycolysis continues
Correct Answer:
Dihydroxyacetone phosphate is converted into glyceraldehyde-3-phosphate, while glyceraldehyde-3-phosphate continues directly
Explanation:
Aldolase produces one glyceraldehyde-3-phosphate and one dihydroxyacetone phosphate. Dihydroxyacetone phosphate is isomerized to glyceraldehyde-3-phosphate, so two molecules of glyceraldehyde-3-phosphate proceed through the later glycolytic reactions.
7. What is the net carbon accounting when one molecule of fructose-1,6-bisphosphate is cleaved by aldolase?
A.
One six-carbon molecule becomes two three-carbon molecules, with no carbon atoms lost
B.
One six-carbon molecule becomes one four-carbon and one two-carbon molecule
C.
One six-carbon molecule becomes three two-carbon molecules, with one carbon oxidized
D.
One six-carbon molecule becomes two three-carbon molecules and one carbon dioxide molecule
Correct Answer:
One six-carbon molecule becomes two three-carbon molecules, with no carbon atoms lost
Explanation:
The aldolase reaction is a carbon-chain cleavage that divides the six-carbon fructose-1,6-bisphosphate into two three-carbon triose phosphates. It does not release carbon dioxide.
8. Which statement best explains why fructose-1,6-bisphosphate cleavage leads to duplication of downstream glycolytic reactions?
A.
Each cleavage product contains three carbons and can be processed as a separate triose phosphate
B.
Each cleavage product contains six carbons and is phosphorylated again
C.
Cleavage creates ATP, which activates two independent glucose molecules
D.
The products recombine before being converted into pyruvate
Correct Answer:
Each cleavage product contains three carbons and can be processed as a separate triose phosphate
Explanation:
The aldolase reaction converts one six-carbon intermediate into two three-carbon intermediates. After dihydroxyacetone phosphate is isomerized, both three-carbon molecules follow the same downstream pathway, doubling the number of substrate molecules for those reactions.
9. A mutation prevents formation of the fructose-1,6-bisphosphate intermediate but does not affect the aldolase enzyme itself. Which immediate consequence is most likely?
A.
Aldolase lacks its six-carbon substrate, so production of the two triose phosphates decreases
B.
Aldolase produces excess triose phosphates directly from glucose without fructose-1,6-bisphosphate
C.
Fructose-1,6-bisphosphate accumulates because its formation is blocked downstream
D.
The two triose phosphates are converted back into fructose-1,6-bisphosphate by aldolase
Correct Answer:
Aldolase lacks its six-carbon substrate, so production of the two triose phosphates decreases
Explanation:
Fructose-1,6-bisphosphate is the substrate for aldolase. If its formation is prevented, aldolase cannot efficiently generate glyceraldehyde-3-phosphate and dihydroxyacetone phosphate.
10. For each molecule of glucose entering glycolysis, how many molecules of fructose-1,6-bisphosphate are formed and how many molecules of glyceraldehyde-3-phosphate ultimately continue beyond the cleavage stage?
A.
One fructose-1,6-bisphosphate and two glyceraldehyde-3-phosphate molecules
B.
Two fructose-1,6-bisphosphate and one glyceraldehyde-3-phosphate molecule
C.
One fructose-1,6-bisphosphate and one glyceraldehyde-3-phosphate molecule
D.
Two fructose-1,6-bisphosphate and four glyceraldehyde-3-phosphate molecules
Correct Answer:
One fructose-1,6-bisphosphate and two glyceraldehyde-3-phosphate molecules
Explanation:
One glucose molecule gives rise to one fructose-1,6-bisphosphate molecule. Aldolase produces one glyceraldehyde-3-phosphate and one dihydroxyacetone phosphate; the latter is isomerized into a second glyceraldehyde-3-phosphate.
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