In gluconeogenesis why the step pyruvate to phoosphoenol pyruvate is bot the reverse reaction of glycolysis?

Question

In gluconeogenesis why the step pyruvate to phoosphoenol pyruvate is bot the reverse reaction of glycolysis?

Answer 1

Because PEP is irreversibly converted to Pyruvate by the activity of Pyruvate kinase. that's why in gluconeogenesis we use a carboxylase to converte it into oxaloacetate.

Answer 2

Because they use different mechanisms.In glycolysis, pyruvate is made when a phosphate is transferred using enzyme pyruvate kinase. In gluconeogenesis, pyruvate first has to get into the cytosol by changing to oxaloacteate, which is then converted to phosphoenolpyruvate by enzyme phosphoenolpyruvatecarboxykinase. In short, gluconeogenesis uses oxaloacteate as a kind of intermediate step, glycolsis does not.