Question

Recall the first three reactions in glycolysis:

You’ve already learned that, in addition to proceeding through glycolysis, glucose 6-phosphate (G6P) can be used to synthesize a carbohydrate storage molecule called glycogen. Glucose 6-phosphate is also a precursor for the synthesis of nucleotides that are used to build DNA and RNA. The first step of this pathway is catalyzed by an enzyme called glucose 6-phosphate dehydrogenase. Assume that reactions in this pathway with double arrows are reversible under cellular conditions, while those with single arrows are effectively irreversible.

The reaction catalyzed by G6P dehydrogenase has a large negative ?G.

Given a solution containing abundant fructose 6-phosphate, which of the following enzymes would you need to include to generate 6-phosphogluconolactone? Assume the solution also contains ATP, ADP, NADP+ and NADPH.

1/Phosphoglucomutase

2/G6P Dehydrogenase

3/G6P Isomerase

4/Hexokinase

5/PFK-1

Answer 1

As the glucose-6-phosphate is the substrate for the reaction catalysed by the glucose-6-phosphate dehydrogenase, the fructose-6-phosphate first must be converted into glucose-6-phosphate in order to make 6-phosphogluconolactone by glucose-6-phosphate dehydrogenase. The conversion of fructose-6-phosphate to glucose-6-phosphate is catalysed by the glucose-6-phosphate isomerase, hence G6P isomerase is required to make 6-phosphogluconolactone from fructose-6-phosphate.