Question

draw the mechanism for aldolase with glucose-6-phosphate that indicates why glucose-6-phosphate is not an appropriate substrate in terms of efficienty having a convergent pathway

Answer 1

The Formation of Fructose 1,6-bisphosphate from Glucose 6-phosphate

One of the initial steps in glycolysis is the isomerization of glucose 6-phosphate to fructose 6-phosphate. The isomerization of glucose 6-phosphate to fructose 6-phosphate is a conversion of an aldose into a ketose.

A second phosphorylation reaction follows the isomerization step. Fructose 6-phosphate is phosphorylated by ATP to fructose 1,6-bisphosphate (F-1,6-BP). The prefix bis- in bisphosphate means that two separate monophosphate groups are present, whereas the prefix di- in diphosphate (as in adenosine diphosphate) means that two phosphate groups are present and are connected by an anhydride bond.

The Six-Carbon Sugar Is Cleaved into Two Three-Carbon Fragments by Aldolase

The second stage of glycolysis begins with the splitting of fructose 1,6-bisphosphate into glyceraldehyde 3-phosphate(GAP) and dihydroxyacetone phosphate (DHAP). The products of the remaining steps in glycolysis consist of three-carbon units rather than six-carbon units.

This reaction is catalyzed by aldolase. This enzyme derives its name from the nature of the reverse reaction, an aldol condensation. The reaction catalyzed by aldolase is readily reversible under intracellular conditions.

Glucose 6-phosphate cannot diffuse through the membrane, because of its negative charges. As well, glucose-6-phosphate is not an appropriate direct substrate in terms of efficiently having a convergent pathway. Its known that hexokinase (HK) phosphorylates glucose to glucose-6-phosphate (G6P) but are not many conditions that this reaction may be reversed that do not involve glucose-6-phosphatase. The reverse reaction is too energetically unfavorable.