Question

4.           Explạin why the following observạtions ạre mạde under prolonged stạrvạtion conditions:

ạ.           The expression levels of enzymes found in the ureạ cycle ạre increạsed

b.           The liver’s ạbility to metạbolize ạcetyl-CoẠ viạ the CẠC is diminished.

Answer 1

Ans 4:

a. During prolonged starvation, body proteins are being actively depleted for the source of energy. this breakdown leads to the increase in the concentration of ammonia into the body. As the toxicity of ammonia is very high so cannot be stored as it is in the body. So it becomes a necessity to convert this highly toxic ammonia into less toxic urea. Urea on concentration would be converted to urine and is excreted out of the body.

Also, the studies suggested that during starvation the urea excretion increases by 200%. Hence the activity of the enzyme associated with this urea excretion is also increased.

b. During the starvation period, the blood sugar level drops down which further leads to a decrease in insulin secretion and an increase in glucagon secretion. The increased glucagon production is in response to low glucose levels.

The main target of the glucagon is the Liver. This glucagon triggers the CAC (cyclic AMP cascade) which results in the activation of phosphorylase and inhibition of glycogen synthase.

Thus the liver's ability to metabolize acetyl CoA via CAC is diminished as the glucagon inhibits the synthesis of fatty acid by keeping them in the unphosphorylated state which further lowers the activity of acetyl CoA.