Which steps must be bypassed in gluconeogenesis?

In gluconeogenesis, specific steps of glycolysis are bypassed due to the irreversible nature of certain enzymatic reactions. These steps correspond to three critical points in the glycolytic pathway: steps 1, 3, and 10.

The first step in glycolysis, catalyzed by hexokinase or glucokinase, involves the conversion of glucose to glucose-6-phosphate. This reaction is irreversible, so during gluconeogenesis, glucose-6-phosphate is synthesized from various substrates (such as pyruvate) rather than going through this step.

The third step is catalyzed by phosphofructokinase-1, which converts fructose-6-phosphate to fructose-1,6-bisphosphate and is also irreversible. In gluconeogenesis, the reverse reaction is achieved through the action of fructose-1,6-bisphosphatase, which bypasses this step.

Finally, step ten involves the conversion of phosphoenolpyruvate to pyruvate, catalyzed by pyruvate kinase, another irreversible step. This is bypassed by converting pyruvate to phosphoenolpyruvate via a series of reactions that include pyruvate carboxylase