Vitamins, Harmones and Hemoglobin
Insulin promotes lipogenesis by the following EXCEPT:(AIIMS May 2008)
|B||Increase glucose uptake in cell|
|C||Inhibiting pyruvate dehydrogenase|
|D||Increase acetyl CoA|
(Ref. Harper’s Illustrated Biochemistry twenty-sixth edition Table 19-1)
a. In adipose tissue, where glucose provides acetyl CoA for lipogenesis, the enzyme is activated in response to insulin.
b. Glucagon is active in heart muscle but not in skeletal muscle.
c. Cyclic AMP (cAMP) is formed from ATP by adenylyl cyclase at the inner surface of cell membranes and acts as an intracellular second messenger in response to hormones such as epinephrine, norepinephrine, and glucagon.
d. cAMP is hydrolyzed by phosphodiesterase, so terminating hormone action. In liver, insulin increases the activity of phosphodiesterase.
e. Insulin also promotes glycogenesis in muscle at the same time as inhibiting glycogenolysis by raising glucose 6-phosphate concentrations, which stimulates the dephosphorylation and activation of glycogen synthase.
f. Cyclic AMP integrates the regulation of glycogenolysis and glycogenesis by promoting the simultaneous activation of phosphorylase and inhibition of glycogen synthase. Insulin acts reciprocally by inhibiting glycogenolysis and stimulating glycogenesis.