6 During fasting the liver pyruvate kinase enzyme is A inhi

6. During fasting the liver pyruvate kinase enzyme is :

                        A. inhibited by phosphorylation by PKA

                        B. activated by phosphorylation by PKA

                        C. located in the mitochondria

D. activated by ATP

_______7. Phosphorylation of glycogen phosphorylase kinase by PKA in the liver:

A. activates of glycogen synthase

B. inactivates of glycogen synthase

C. inactivates of glycogen phosphorylase kinase

D. activates of glycogen phosphorylase kinase

_____8. In the skeletal muscle when a football player runs sprints during practice, the NADH produced in glycolysis at the glyceraldehydes 3-phosphate step is re-oxidized primarily by:

                        A. Malate dehydrogenase

                        B. Lactate dehydrogenase

                        C. Pyruvate dehydrogenase

                        D. Isocitrate dehydrogenase

_____9. Which of the following compounds is an allosteric activator of pyruvate carboxylase?

                        A. Biotin

                        B. Acetyl CoA

                        C. NADH

                        D. insulin

______10. Fatty acids with an odd number of carbon atoms and certain branched-chain fatty acids can support the net synthesis of glucose because they:

                        A. are converted to acetoacetate and -hydroxybutyrate

                        B. are converted to malonyl-CoA

                        C. can produce propionyl-CoA which is converted to succinyl-CoA

                        D. Increase the NAD/NADH ratio

Solution

Answer 6. = A. During fasting blood glucose is exhausted or is at low levels. In this state bosy can not afford to metabolize glucose into pyruvate anymore (glycolysis). To bring back blood glucose level for survival of brain, the enzyme pyruvate kinase (of glycolysis) is deactivated through phosphorylation.This prevents conversion of phosphoenol pyruvate to pyruvate. This phosphoenol pyruvate is used up in recreating glucose through gluconeogenesis process.

Answer 7. = D. Phosphorylation of glycogen phosphorylase kinase by PKA in the liver activates glycogen phosphorylase kinase enzyme. This is responsible for catalysis of glycogen in to glucose-1-phosphate.

Answer 8. = B. Lectate dehydrogenase is responsible for re-oxidation of NADH generated in glycolysis. This is called fermentation. This is the cause of muscular fatigue.

Answer 9. = B. Acetyl Co-A is an allosteric activator of pyruvate carboxylase enzyme. This mechanism is utilized in conversion of pyruvate into oxaloacetate.

Answer 10. = C. Fatty acids with an odd number of carbon atoms and certain branched-chain fatty acids can support the net synthesis of glucose because they can produce propionyl-CoA which is converted to succinyl-CoA. Even numbered fatty acids are not known to be utilized in the reaction.