Question

When gluconeogenesis is activated during fasting in liver, glycolysis slows. How does this happen?

a. pyruvate kinase and pyruvate dehydrogenase are both inhibited by phosphorylation in response to a decreased insulin/glucagon ratio

b. PFK-2 is phosphorylated

c. acetyl CoA allosterically inhibits pyruvate dehydrogenase

d. acetyl CoA allosterically activates pyruvate carboxylase

e. all of the above

Answer 1

Q1.
High glucagon/insulin ratio causes elevated cAMP and increased licveks of active protein kinase A. Increased protein kinase A activity favours the phosphorylated form of the bifunctional PFK-2/FBP-2. Phosphorylation of PFK -2 domain inactivated it, allowing FBP-2 domain to active. It causes hydrolysis of fructose-2,6-bisphosphate. Decreased levels of fructose 2,6 bisphosphate decrease the inhibition of FBP-1, which leads to an increased rate of gluconeogenesis.

Ans is Option E - all of the above.

decresed insulin levels decreases the activity of phosphatase enzyme and causes increase in phosphorylation of various enzyme including pyruvate kinase and PDH complex.
'as cells need glucose, acetyl coA formed will alloesterically inhibit PDH complex and activate pyruvate carboxylate to channel all the pyruvateaway from TCA cycle and increase the formation of oxaloacetate as the first step of gluconeogenesis.