Q.81 Which of the following reactions is/are catalyzed by aldolase?
(A) Dihydroxyacetone phosphate + Glyceraldehye–3–phosphate → Fructose 1,6–
biphosphate
(B) Dihydroxyacetone phosphate + Erythrose–4–phosphate → Sedoheptulose–1,7–
biphosphate
(C) Dihydroxyacetone phosphate → Glyceraldehyde–3–phosphate
(D) Glyceraldehye–3–phosphate + Erythrose–4–phosphate → Sedoheptulose–1,7–
biphosphate

Aldolase catalyzes two specific aldol condensation reactions among the given options in glycolysis and the Calvin cycle. Options (A) and (B) are correct, while (C) and (D) are not.

Option Analysis

Option (A): Dihydroxyacetone phosphate (DHAP) + Glyceraldehyde-3-phosphate (G3P) → Fructose 1,6-bisphosphate (F1,6BP).
This reverse aldol reaction occurs in gluconeogenesis and the Calvin cycle’s regeneration phase, where aldolase condenses the two triose phosphates to form the six-carbon F1,6BP.​

Option (B): DHAP + Erythrose-4-phosphate → Sedoheptulose-1,7-bisphosphate.
Aldolase catalyzes this in the Calvin cycle, forming the seven-carbon sedoheptulose-1,7-bisphosphate from a triose and tetrose phosphate during RuBP regeneration.​

Option (C): DHAP → G3P.
This isomerization maintains equilibrium between the triose phosphates but is catalyzed by triose-phosphate isomerase, not aldolase.​

Option (D): G3P + Erythrose-4-phosphate → Sedoheptulose-1,7-bisphosphate.
Transaldolase, not aldolase, handles this transfer in the Calvin cycle; aldolase requires DHAP as the ketose partner.​

Aldolase catalyzed reactions play a pivotal role in carbohydrate metabolism, particularly the condensation of dihydroxyacetone phosphate (DHAP) with glyceraldehyde-3-phosphate (G3P) to form fructose 1,6-bisphosphate (F1,6BP) in glycolysis reversal and gluconeogenesis. These reactions are essential for CSIR NET Life Sciences aspirants studying enzyme functions in metabolic pathways like the Calvin cycle. Understanding which substrates aldolase acts on—such as DHAP paired with aldoses—helps differentiate it from enzymes like triose-phosphate isomerase or transaldolase.

Key Aldolase Functions

• Catalyzes reversible aldol condensations forming C-C bonds between ketose (DHAP) and aldose phosphates.​

• In glycolysis: Cleaves F1,6BP to DHAP + G3P; reverse in gluconeogenesis.​

• In Calvin cycle: Two reactions—DHAP + G3P → F1,6BP and DHAP + erythrose-4-phosphate → sedoheptulose-1,7-bisphosphate—for RuBP regeneration.​

Common Exam Confusions

CSIR NET questions often test specificity: Aldolase does not isomerize DHAP to G3P (triose-phosphate isomerase) or use two aldoses like G3P + erythrose-4-phosphate (transaldolase). Class I aldolases (Schiff base mechanism) dominate in animals, while Class II use metals in plants/bacteria.​

Master these aldolase catalyzed reactions for competitive exams by focusing on substrate pairs and pathway context.