Question

What is the significance of the isomerization of glucose 6-phosphate to fructose 6-phosphate for the progression of glycolysis?

• A. As functional groups, ketones are more reactive than aldehydes
• B. Cleavage of glucose 1,6-bisphosphate will not yield dihydroxyacetone phosphate and glyceraldehyde 3-phosphate
• C. The carbonyl group at carbon-2 (C-2) in fructose facilitates the cleavage of the bond between C-3 and C-4
• D. Phosphorylation of glucose 6-phosphate to glucose 1,6-bisphosphate is irreversible

Hint:

In glycolysis, the shift from aldose (glucose) to ketose (fructose) allows symmetric cleavage into two 3-carbon intermediates.

Answer 1

The Correct Option is C

Step 1: Recall the step in glycolysis.
In glycolysis, glucose-6-phosphate (an aldose) is isomerized to fructose-6-phosphate (a ketose) by the enzyme phosphoglucose isomerase.
Step 2: Role of isomerization.
This conversion moves the carbonyl group from C-1 to C-2, forming a ketose. This change enables the molecule to later form a symmetrical 6-carbon intermediate that can be split evenly into two 3-carbon compounds.
Step 3: Importance for cleavage.
During the aldolase step, fructose 1,6-bisphosphate splits into dihydroxyacetone phosphate and glyceraldehyde 3-phosphate — a reaction that is possible only because the carbonyl group is positioned at C-2.
Step 4: Conclusion.
Therefore, the isomerization to fructose 6-phosphate ensures proper bond cleavage between C-3 and C-4.