Question

Which of the following accurately accounts for why gluconeogenesis is NOT simply the reverse of glycolysis?

A) Gluconeogenesis is reciprocally and oppositely regulated with glycolysis.
B) Gluconeogenesis is reciprocally and oppositely regulated with glycolysis.
C) Gluconeogenesis makes more ATP than glycolysis, so it is endergonic
D) Three steps of glycolysis are highly exergonic and require different enzymes to reverse.

Answer 1

Gluconeogenesis is not the reverse of glycolysis and involves specific bypass reactions and enzymes. Pyruvate is converted into oxaloacetate, which is then transformed into phosphoenolpyruvate (PEP). These differences in enzyme activity allow the cell to regulate glycolysis and gluconeogenesis independently.

Step-by-step explanation:

Gluconeogenesis is not simply the reverse of glycolysis. There are some important differences. In gluconeogenesis, pyruvate is converted into oxaloacetate, which then serves as a substrate for the enzyme phosphoenolpyruvate carboxykinase (PEPCK). PEPCK transforms oxaloacetate into phosphoenolpyruvate (PEP), and from this step, gluconeogenesis is nearly the reverse of glycolysis.

However, there are three biologically irreversible reactions in glycolysis that are bypassed in gluconeogenesis. These bypass reactions involve specific enzymes that are only found in the gluconeogenesis pathway. For example, the enzyme hexokinase in glycolysis is replaced by glucose-6-phosphatase in gluconeogenesis, and the enzyme phosphofructokinase-1 in glycolysis is replaced by fructose-1,6-bisphosphatase in gluconeogenesis. These differences allow the cell to regulate glycolysis and gluconeogenesis independently of each other.