Date: 06. December 2016
In this video lecture, educator introduces the process of glucogeonesis, which is conversion of non-carbohydrates precursors to glucose or glycogen. Reactions of Gluconeogenesis consists of three bypass. 1. First bypass (Formation of Phosphoenolpyruvate from pyruvate) 2. Second bypass (Formation of Fructose 6-Phosphate from Fructose 1,6-Bisphosphate) 3. Third bypass (Formation of Glucose by Hydrolysis of Glucose 6-Phosphate).
In first bypass, mitochondrial pyruvate carboxylase catalyzes the carboxylation of pyruvate to oxaloacetate. Oxaloacetate is reduced to malate inside the mitochondrion for transport to the cytosol. Phosphoenolpyruvate carboxy kinase, catalyzes the decarboxylation and phosphorylation of oxaloacetate to phosphoenolpyruvate.
Gluconeogenesis is biologically very significant. In second bypass phosphoenolpyruvate is metabolized by the enzymes of glycolysis but in the reverse direction. Fructose 1,6-bisphosphatase catalyzes this exergonic hydrolysis.
In third bypass the fructose 6-phosphate generated by fructose 1,6-bisphosphatase is readily converted into glucose 6-phosphate. Final step in the generation of glucose does not take place in the cytosol.
Substrates of gluconeogenesis are 1. Glycogenic amino acids 2. Lactate 3. Propionate. Entry of glycogenic amino acids occurs by pyruvate, oxalo acetate, α-Ketoglutarate, Succinyl CoA and Fumarate.
Contracting skeletal muscle supplies lactate to the liver, which uses it to synthesize glucose. These reactions constitute the Cori cycle. In non-ruminants, including humans, propionate arises from the Beta -oxidation of odd-chain fatty acids. Entry of glycerol in to the pathway of gluconeogenesis takes place from many places.
Gluconeogenesis and glycolysis are coordinated so that within a cell one pathway is relatively inactive while the other is highly active. Educator also explains induction and repression of key enzymes. Covalent modification by reversible phosphorylation is a rapid process. While allosteric modification is an instantaneous process. Reciprocal Regulation of Gluconeogenesis and Glycolysis occurs in liver.
Gluconeogenesis is clinically very significant. Hypoglycemia in premature and low birth weight infants and babies of diabetic mothers. Gluconeogenesis plays vital role in human kidney.