Question

Explain the chemical logic of converting glucose to fructose before aldolase splits the sugar in two.

Short answer

$\begin{array}{l}\mathrm{Glucose}-1,6-\mathrm{phosphate}\stackrel{\mathrm{isomerase}}{\to }\mathrm{Fructos}-1,6-\mathrm{bisphosphate}\\ \mathrm{Fructose}-1,6-\mathrm{bisphosphate}\stackrel{\mathrm{Aldolase}}{\to }\mathrm{Dihydroxyacetonephosphate}+\mathrm{Glyceraldehyde}-3-\mathrm{phosphate}\end{array}$

Step-by-step solution

Introduction

Cellular respiration is the mechanism by which metabolic processes receive energy in the form of ATP from nutrients.

Converting the glucose to fructose

The glucose-6-phosphate generated can be shuttled to other metabolic routes, such as the pentose phosphate pathway, therefore the first step of glycolysis is not the committed phase. Phosphofructokinase-1 converts fructose-6-phosphate to fructose-1,6-bisphosphate, which is the only committed step in glycolysis. Glucose-6-phosphate must first be converted to fructose-6-phosphate in this stage.

Two phosphate groups are linked to fructose-1,6-bisphosphate: one at C-1 and the other at C-6. C-1 is an aldehyde group that cannot be phosphorylated in the structure of glucose; it is first transformed to an alcoholic group by molecular interconversion with C-2, which is then converted to a ketone. Because the ∆G° value for this reaction is so tiny, it happens quickly in the opposite direction. Fructose-1,6 bisphosphate is generated because both C1 and C6 have hydroxyl groups that can be phosphorylated.

The aforementioned glucose to fructose-1,6-biphosphate conversion occurs so that the enzyme aldolase may break the carbon-carbon bond and produce two sugars. Fructose receptors are unique to the aldolase enzyme.