Gluconeogenesis lec 1
- 2. Gluconeogenesis is the process of converting noncarbohydrate precursors to glucose Gluconeogenesis meets the needs of the body for glucose when sufficient carbohydrate is not available from the diet or glycogen reserves. Some tissues, such as the brain, red blood cells, kidney medulla, lens and cornea of the eye, testes, and exercising muscle, require a continuous supply of glucose as a metabolic fuel. Liver glycogen, an essential postprandial source of glucose, can meet these needs for only 10–18 hours in the absence of dietary intake of carbohydrate.
- 3. Substrates of Gluconeogenesis Non carbohydrate precursors are, • Glycerol • Lactate • α- ketoacid • Glucogenic amino acids Liver and the kidney are major gluconeogenic tissues.
- 5. Fate of lactic acid
- 7. • Occurs mainly in liver and to a limited extent in kidney. • Synthesis of glucose from pyruvate utilizes many of the same enzymes as Glycolysis. • Three Glycolysis reactions are essentially irreversible. • Hexokinase (or Glucokinase) • Phosphofructokinase • Pyruvate Kinase • These steps must be bypassed in Gluconeogenesis. • The first two of the bypass reactions involve simple hydrolysis reactions.
- 8. • within 2 hours after a meal, glycogenolysis is stimulated and begins to supply glucose to the blood. Subsequently, glucose is also produced by gluconeogenesis. • During a 12-hour fast, glycogenolysis is the major source of blood glucose. Thus, it is the major pathway by which glucose is produced in the basal state (after a 12- hour fast). However, by approximately 16 hours of fasting, glycogenolysis and gluconeogenesis contribute equally to the maintenance of blood glucose. • By 30 hours after a meal, liver glycogen stores are substantially depleted. Subsequently, gluconeogenesis is the primary source of blood glucose. • The mechanisms that cause fats to be used as the major fuel and that allow blood glucose levels to be maintained during periods of food deprivation result in the conservation of body protein and, consequently, permit survival during prolonged fasting for periods often exceeding 1 or more months.