A genetic disorder renders fructose 1,6 — bisphosphates in liver less sensitive to regulation by fructose 2,6 — bi-phosphate. All of the following metabolic changes are observed in this disorder except:
**Core Concept**
Fructose 1,6-bisphosphatase is a key enzyme in gluconeogenesis, and its activity is tightly regulated by fructose 2,6-bisphosphate. In the liver, fructose 2,6-bisphosphate acts as a potent allosteric inhibitor of fructose 1,6-bisphosphatase, thereby promoting glycolysis and inhibiting gluconeogenesis. A genetic disorder rendering fructose 1,6-bisphosphatase less sensitive to regulation by fructose 2,6-bisphosphate would disrupt this regulatory mechanism.
**Why the Correct Answer is Right**
In the absence of effective regulation by fructose 2,6-bisphosphate, fructose 1,6-bisphosphatase would continue to catalyze the conversion of fructose 1,6-bisphosphate to fructose 6-phosphate, even in the presence of high levels of fructose 2,6-bisphosphate. As a result, the level of fructose 1,6-bisphosphate would be expected to decrease, as it is being converted to fructose 6-phosphate. This decrease in fructose 1,6-bisphosphate levels would, in turn, lead to a decrease in the formation of pyruvate and ATP. Therefore, option A, which states that the level of fructose 1,6-bisphosphate is higher than normal, is incorrect.
**Why Each Wrong Option is Incorrect**
**Option B:** This option states that the level of fructose 1,6-bisphosphate is lower than normal, which is consistent with the expected outcome of a genetic disorder rendering fructose 1,6-bisphosphatase less sensitive to regulation by fructose 2,6-bisphosphate.
**Option C:** This option states that less pyruvate is formed, which is a correct consequence of the decreased activity of fructose 1,6-bisphosphatase.
**Option D:** This option states that less ATP is formed, which is also a correct consequence of the decreased activity of fructose 1,6-bisphosphatase.
**Clinical Pearl / High-Yield Fact**
In the liver, the regulation of fructose 1,6-bisphosphatase by fructose 2,6-bisphosphate is a critical mechanism for controlling the balance between glycolysis and gluconeogenesis. Understanding this regulatory mechanism is essential for understanding the pathophysiology of metabolic disorders, such as diabetes and liver disease.
**✓ Correct Answer: A. Level of fructose 1,6--biphosphate is higher than normal**