Passage
Glycolysis and gluconeogenesis are tightly regulated, opposing metabolic pathways that help control blood glucose levels. Glycolysis converts glucose to two pyruvate molecules, whereas gluconeogenesis consumes 6 ATP equivalents to convert two pyruvate molecules back to glucose. When glycolysis is upregulated, gluconeogenesis is downregulated, and vice versa.As shown in Figure 1, glycolysis and gluconeogenesis in the liver are largely regulated by the allosteric action of the small molecule fructose-2,6-bisphosphate (F2,6BP) on the enzymes phosphofructokinase-1 (PFK-1) and fructose-1,6-bisphosphatase (F1,6BPase) . PFK-1 is a kinase that uses ATP to phosphorylate fructose-6-phosphate (F6P) in an irreversible step of glycolysis, forming fructose-1,6-bisphosphate (F1,6BP) and ADP. During gluconeogenesis, F1,6BPase removes the phosphate group by hydrolysis.
Figure 1 Activities of (A) PFK-1 and (B) F1,6BPase in the presence (solid lines) and absence (dashed lines) of F2,6BPA bifunctional enzyme that contains a phosphofructokinase-2 (PFK-2) domain and a fructose-2,6-bisphosphatase (F2,6BPase) domain controls F2,6BP levels in the liver. The PFK-2 domain converts F6P to F2,6BP, and the F2,6BPase domain converts F2,6BP back to F6P. When blood glucose levels are low, the enzyme becomes phosphorylated. This phosphorylation event simultaneously activates the F2,6BPase domain and inactivates the PFK-2 domain. Under high blood glucose conditions, the enzyme becomes dephosphorylated, activating the PFK-2 domain and inactivating the F2,6BPase domain.
-The information in the passage and the data in Figure 1 support the conclusion that when glycolysis is active, the bifunctional PFK-2/F2,6BPase enzyme is:

Question

Passage
Glycolysis and gluconeogenesis are tightly regulated, opposing metabolic pathways that help control blood glucose levels. Glycolysis converts glucose to two pyruvate molecules, whereas gluconeogenesis consumes 6 ATP equivalents to convert two pyruvate molecules back to glucose. When glycolysis is upregulated, gluconeogenesis is downregulated, and vice versa.As shown in Figure 1, glycolysis and gluconeogenesis in the liver are largely regulated by the allosteric action of the small molecule fructose-2,6-bisphosphate (F2,6BP) on the enzymes phosphofructokinase-1 (PFK-1) and fructose-1,6-bisphosphatase (F1,6BPase) . PFK-1 is a kinase that uses ATP to phosphorylate fructose-6-phosphate (F6P) in an irreversible step of glycolysis, forming fructose-1,6-bisphosphate (F1,6BP) and ADP. During gluconeogenesis, F1,6BPase removes the phosphate group by hydrolysis.

Figure 1 Activities of (A) PFK-1 and (B) F1,6BPase in the presence (solid lines) and absence (dashed lines) of F2,6BPA bifunctional enzyme that contains a phosphofructokinase-2 (PFK-2) domain and a fructose-2,6-bisphosphatase (F2,6BPase) domain controls F2,6BP levels in the liver. The PFK-2 domain converts F6P to F2,6BP, and the F2,6BPase domain converts F2,6BP back to F6P. When blood glucose levels are low, the enzyme becomes phosphorylated. This phosphorylation event simultaneously activates the F2,6BPase domain and inactivates the PFK-2 domain. Under high blood glucose conditions, the enzyme becomes dephosphorylated, activating the PFK-2 domain and inactivating the F2,6BPase domain.
-The information in the passage and the data in Figure 1 support the conclusion that when glycolysis is active, the bifunctional PFK-2/F2,6BPase enzyme is:

Quizplus · Accepted Answer

11ecba2d_0f10_3e02_a3bf_271e7c3ca764_MD0008_00 The rate of glycolysis is largely controlled by PFK-1 activity. When PFK-1 is active, glycolysis proceeds quickly, whereas when PFK-1 activity is downregulated, glycolysis is slow. PFK-1 is tightly regulated by several allosteric effectors, including the inhibitors ATP and citrate and the activators ADP, AMP, and F2,6BP. The data in Figure 1 confirm that PFK-1 is most active when F2,6BP is present, indicating that glycolysis is most active when F2,6BP is abundant. Therefore, conditions that promote glycolysis most likely also promote F2,6BP synthesis. Because the PFK-2 domain produces F2,6BP, it must be active during glycolysis. The passage states that the PFK-2 domain of the bifunctional enzyme is active (and the F2,6BPase domain is inactive) when it is dephosphorylated. Therefore, when glycolysis is active, the PFK-2/F2,6BPase enzyme is most likely dephosphorylated and produces F2,6BP. (Choice A) When the PFK-2/F2,6BPase enzyme is phosphorylated, the F2,6BPase domain is active and consumes F2,6BP. However, this occurs when gluconeogenesis, not glycolysis, is active. (Choice B) If PFK-2/F2,6BPase were phosphorylated, it would consume F2,6BP, converting it to F6P, and stimulate gluconeogenesis rather than glycolysis. (Choice C) When PFK-2/F2,6BPase is dephosphorylated, it produces F2,6BP to stimulate glycolysis, rather than consumes F2,6BP. Educational objective: The rate of glycolysis is controlled by PFK-1, which is stimulated by the allosteric effector F2,6BP. When glycolysis is active, F2,6BP synthesis is also most likely active.

Passage Glycolysis and Gluconeogenesis Are Tightly Regulated, Opposing Metabolic Pathways That