Glükeogeneesiin

Glükeogeneesiin is the metabolic process by which glucose is synthesized from non-carbohydrate precursors. This biochemical pathway is crucial for maintaining blood glucose homeostasis, particularly during fasting, starvation, or prolonged exercise when dietary glucose intake is insufficient. The primary sites for gluconeogenesis in mammals are the liver and the kidneys.

The process begins with the conversion of precursors such as lactate, pyruvate, glycerol, and certain amino acids into glucose. While the overall pathway resembles glycolysis in reverse, there are key enzymatic steps that are different to bypass the irreversible reactions of glycolysis. For instance, pyruvate carboxylase and phosphoenolpyruvate carboxykinase are essential enzymes that catalyze the conversion of pyruvate to phosphoenolpyruvate, a step not present in glycolysis. Other bypass enzymes include fructose-1,6-bisphosphatase and glucose-6-phosphatase.

Lactate, a byproduct of anaerobic respiration, can be transported to the liver and converted back to pyruvate, which then enters the gluconeogenic pathway. Glycerol, derived from the breakdown of triglycerides in adipose tissue, can be phosphorylated and enter the pathway at the dihydroxyacetone phosphate stage. Amino acids, when catabolized, can yield intermediates like pyruvate or oxaloacetate that are also substrates for gluconeogenesis.

Gluconeogenesis is an energy-requiring process, consuming ATP and GTP. It is tightly regulated by hormones such as glucagon and cortisol, which stimulate the pathway, and insulin, which inhibits it. This regulation ensures that glucose is produced when needed and conserved when blood glucose levels are adequate. The ability to synthesize glucose de novo is vital for tissues that rely heavily on glucose as their primary energy source, such as the brain and red blood cells.