Question

Under prolonged starvation conditions, certain pathways are upregulated. For each of the following, indicate 1) the purpose or outcome of the pathway, 2) why it would need to be upregulated under starvation and 3) what organ(s) or tissue(s) are involved and their role(s).

a. Gluconeogenesis

b. Glucose-Alanine Cycle

c. Ketogenesis

d. Urea Cycle

Answer 1

a. Gluconeogenesis forms glucose from sources other than carbohydrates. It will increase glucose levels by burning mostly fatty acids or fats and amino acids. It occurs in liver. Under starvation this process increases glucose levels of blood.

b. Glucose-Alanine cycle is a gluconeogenetic path way. In the muscles  the alanine is converted in to pyruvate . It is transports (alanine) nitrogen in non-toxic form to liver from muscles.In the liver it is converted back to pyruvtae which is used in forming glucose. This increases glucose levels in blood during starvation. Amino group enters in to urea cycle.

It occurs in skeletal muscles and liver.

c.Ketogenesis is production of ketone bodies by break down of fatty acids, keto amino acids. The process occurs during fasting. This  inceases the blood glucose levels during starvation.

They are produced in mitochondria of liver cells.

d. Urea cycle--This cycle occurs in liver. Amino acids deamination occurs when glucose has to be formed by gluconeogenesis.. During this process ammonia is liberated which is carried in to urea cycle to form urea. Urea cycle reduces the ammonium ions in blood to maintain blood pH.Starvation results in gluconeogenesis which increases blood ammonia level. The urea cycle decreases blood ammonia levels.

It occurs in liver.