Levels of a signaling molecule, F-2, 6-BP, regulate glycolysis and gluconeogenes

Question

Levels of a signaling molecule, F-2, 6-BP, regulate glycolysis and gluconeogenesis. The target enzymes are phosphofructokinase 1 in glycolysis and fructose-1, 6-bisphosphatase in gluconeogenesis. Use this information to answer the question. The graph shows the activity of fructose-1, 6-bisphosphatase in the presence and absence of F-2, 6-BP. Which statement below is NOT supported by the information provided in the graph? Fructose-1, 6-bisphosphatase activity is the highest when F-2, 6-BP levels are low. Decreasing levels of F-2.6-BP decrease the K_m of fructose-1, 6-bisphosphatase. The absence of F-2, 6-BP increases the affinity of fructose-1, 6-bisphosphatase for its substrate. In the presence of F-2, 6-BP, fructose-1, 6-bispbosphatase activity is completely inhibited.

Explanation / Answer

Answer:     In the presence of F-2,6-BP, fructose-1,6-bisphosphatase activity is completely inhibited.

Fructose 2,6-bisphosphate strongly stimulates phosphofructokinase and inhibits fructose 1,6-bisphosphatase. Glycolysis in the liver responds to changes in blood glucose through the signaling molecule; fructose 2,6-bisphosphate.F-2,6-BP is a potent activator of phosphofructokinase. In the liver the concentration of fructose 6-phosphate rises when blood glucose is high, the abundance of fructose 6-phosphate accelerates the synthesis of F-2,6-BP. F-2,6-BP increases the affinity of phosphofructokinase and diminishes the inhibitory effect of ATP. Thus glycolysis is accelerated when glucose is abundant, a process known as feed-forward stimulation.

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