Odd chain fatty acids can form glucose by which pathway?
Ans: (a) By forming Propionyl CoARef: Harper, Illustrated Biochemistry, 30th edition, Page 225, 558; Styer Biochemistry, 7th edition, Page 650Fatty acids with an odd number of carbon atoms are oxidized by the pathway of (3-oxidation, producing acetyl CoA (2C) until a three-carbon (propionyl-CoA) residue remains.End product of even chain FA oxidation-acetyl CoA(2C).End product of odd chain FA oxidation-acetyl CoA units + 1 propionyl CoA(3C).Propionyl CoA is converted to succinyl-CoA (steps mentioned below), a constituent of the citric acid cycle, which after few steps, enters in to gluconeogenesis.Only 2 enzymes in our body requires vit B as cofactor:Methyl malonyl CoA mutase (AKA methylmalonyl-CoA isomerase).Methionine synthase (Synthesis of Methionine by methylation of homocysteine).Hence, the propionyl residue from an odd-chain fatty acid is the only part of a fatty acid that is glucogenic.Even chain fatty acids cannot synthesize glucose, because PDH reaction is irreversible.Gluconeogenesis is glucose synthesized from non-carbohydrate sources like lactate, propionyl CoA and Glucogenic amino acids. So glucose derived from glycogen break down (carbohydrate source) is NOT gluconeogenesis.
By forming Propionyl CoA
By forming Glycerol
Acetyl CoA entering TCA cycle
By Lactic acid formation
Enzymes