Advanced Dental Admission Test (ADAT)

What is the rate-limiting enzyme for gluconeogenesis?

1. Isocitrate dehydrogenase

2. Fructose bisphosphatase 2

3. Phosphofructokinase

4. Hexokinase

The correct answer is: Fructose bisphosphatase 2

The rate-limiting enzyme for gluconeogenesis is fructose bisphosphatase 2. This enzyme plays a crucial role in the conversion of fructose 1,6-bisphosphate to fructose 6-phosphate, a key step in the gluconeogenesis pathway. As gluconeogenesis is the metabolic process of synthesizing glucose from non-carbohydrate precursors, the regulation of this pathway is vital, especially during fasting or low-carbohydrate intake when the body needs to produce glucose to maintain blood sugar levels. Fructose bisphosphatase 2 is primarily controlled by hormonal regulation, particularly by insulin and glucagon, affecting its activity in response to the body's metabolic state. High levels of fructose 2,6-bisphosphate inhibit this enzyme, while low levels promote gluconeogenesis, highlighting its importance in metabolic control. Understanding this mechanism is essential for grasping how the body maintains glucose homeostasis and how various metabolic pathways are interlinked. The other enzymes listed operate primarily in glycolysis or other metabolic pathways but do not serve as the critical regulatory point for gluconeogenesis.