Odd chain fatty acids can form glucose by which pathway?
Correct Answer: By forming Propionyl CoA
Description: 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.
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