3. Determine under what circumstances does the bifunctional protein phosphofruct

Question

3. Determine under what circumstances does the bifunctional protein phosphofructokinase- 2/fructose 2,6-bisphosphatase (PFK-2/FBPase-2) become phosphorylated, and what are the consequences of its phosphorylation to the glycolytic and gluconeogenic pathways. Circle the correct options below and arrange them in order: Hint: Eliminate the options that are incorrect, rearrange the remaining three answers. See Figs. 15-16 through 15-19 Insulin, signaling low blood sugar, stimulates cAMP synthesis, which activates protein kinase A (PKA) to phosphorylate PFK-2/FBPase-2. Insulin, signaling high blood sugar, stimulates cAMP synthesis, which activates protein kinase A (PKA) to phosphorylate PFK-2/FBPase-2. Glucagon, signaling low blood sugar, stimulates cAMP synthesis, which activates protein kinase A (PKA) to phosphorylate PFK-2/FBPase-2. Glucagon, signaling high blood sugar, stimulates cAMP synthesis, which activates protein kinase A (PKA) to phosphorylate PFK-2/FBPase-2. In the absence of F26BP as an allosteric effector, the activity of PFK-1 is reduced (inhibiting glycolysis) and the activity of FBPase-1 is enhanced (stimulating gluconeogenesis), thus enabling the liver to replenish blood glucose This phosphorylation enhances FBPase-2 activity and inhibits PFK-2 activity of the enzyme, resulting in lower levels of fructose 2,6-bisphosphate (F26BP). a. b. c. d. c. f. Specify the order of events and ,

Explanation / Answer

First we will eliminate the incorrect options.

Insulin senses high blood sugar and activates phosphoprotein phosphatase not PKA. So options a and b are incorrect.

Also we know that Glucagon senses low blood sugar and not high sugar level. So option d is also incorrect.

The correct options are c , e and f.

And the correct order of events is c, f and e.

When PKA is activated, it phosphorylates the bifunctional protein PFK-2/FBPase. This phosphorylation enhances its FBPase-2 activity and inhibits its PFK-2 activity. This lowers the level of F26BP. In this way PFK-1 is inhibited and FBPase-1 is enhanced.

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