True about gluconeogenesis ?

Ans. is 'c' i.e., Alanine & lactate both can serve as substrateSynthesis of glucose from noncarbohydrate precursors is called gluconeogenesis i.e., synthesis of new glucose. The major noncarbohydrate precursors (substrate) for gluconeogenesis are lactate, pyruvate, glycerol, glucogenic amino acids, propionate and intermediates of the citric acid cycle.All aminoacids, except for leucine and lysine, are substrate for gluconeogenesis.Alanine is the most impoant gluconeogenic amino acid.Gluconeogenesis occurs mainly in the liver and to a lesser extent in renal coex.Some gluconeogenesis can also occur in small intestine, but it is not significant.Some of the reactions of gluconeogenesis occurs in the mitochondria but most occur in cytosol. Gluconeogenesis involves glycolysis, the citric acid cycle plus some special reactions.Glycolysis and gluconeogenesis share the same pathway but in opposite direction.Seven reactions of glycolysis are reversible and therefore are used with same enzyme in the synthesis of glucose by gluconeogenesis.However, three of the reactions of glycolysis are irreversible and must be circumvented by four special reactions which are unique to gluconeogenesis and catalyzed by : (1) Pyruvate carboxylase, (ii) Phosphoenolpyruvate carboxykinase, (iii) Fructose-1,6-bisphosphatase, (iv) Glucose-6-phosphatase.These four enzymes are the key enzymes of gluconeogenesis (or gluconeogenesis enzymes).Among these four, pyruvate carboxylase is a mitocondrial enzyme and other three are cytoplasmic enzymes.