4. on a typical, day-to-day basis, the liver performs gluconeogenesis at a low r

Question

4. on a typical, day-to-day basis, the liver performs gluconeogenesis at a low rate. But the liver can perform gluconeogenesis at a high rate, when necessary. (a) Describe gluconeogenesis in general (no detailed metabolic pathways necessary). What are three possible substrates? (1pt) (b) How does gluconeogenesis contribute to homeostasis? (1pt) (c) Under what conditions is the body likely to engage in large-scale gluconeogenesis? Provide two examples with explanations. (2pts) *Reminder: in order to receive full credit, sources must be cited for each question.

Explanation / Answer

a. Gluconeogenesis is a metabolic pathway that results in the generation of glucose from certain non-carbohydrate carbon substrates. These include 1. Glucogenic amino acids like Alanine, Aspertate, Tyrosine, Isoleucine & Argenine); 2. Lipid breakdown products such as glycerol; 3. Metabolic intermediates that include pyruvate and lactate.

b. Homeostasis is the property of a living system within the body of a living organism in which a variable, such as the concentration of a substance in solution, is actively regulated to remain very nearly constant. During sleep or in between meals, when blood glucose levels are low, glucagon is released from -cells to promote hepatic glycogenolysis. In addition, glucagon drives hepatic and renal gluconeogenesis to increase endogenous blood glucose levels during prolonged fasting. In contrast, insulin secretion from -cells is stimulated by elevated exogenous glucose levels, such as those occurring after a meal. After docking to its receptor on muscle and adipose tissue, insulin enables the insulin-dependent uptake of glucose into these tissues and hence lowers blood glucose levels by removing the exogenous glucose from the blood stream by promoting Glycogenesis, Lipogenesis etc.

c. During sleep or in between meals, when blood glucose levels are low, glucagon is released from -cells to promote hepatic glycogenolysis. In addition, glucagon drives hepatic and renal gluconeogenesis to increase endogenous blood glucose levels during prolonged fasting.

References: 1. Silva, Pedro. "The Chemical Logic Behind Gluconeogenesis". Retrieved September 8, 2009.

2. Gerich JE, Meyer C, Woerle HJ, Stumvoll M (2001). "Renal gluconeogenesis: Its importance in human glucose homeostasis". Diabetes Care. 24 (2): 382–391.

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