Question

Why are lipids, but not fatty acids can be used for gluconeogenesis? Use specific names of pathways, enzymes, and molecules to support your explanations.

Answer 1

Gluconeogenesis is the process by which glucose is produced for catabolic reactions from non carbohydrate sources. In humans lipids especially breakdown of triglycerides-glycerol is an important precursor for gluconeogenesis along with amino acids such as alanine and glutamine. The beta-oxidation of the glycerol and branched and odd chain fatty acids produces propionate which is oxidized to pyruvate and in-turn oxaloacetate is formed, from which phosphoenolpyruvate is formed and again from which glucose is generated. But fatty acids cannot be a source for gluconeogenesis because the beta oxidation of fatty acids produces acetyl CoA which on entering Krebs cycle or the citric acid cycle is completely oxidised and results in generation of carbon dioxide instead of forming oxaloacetate. Hence lipids, but not fatty acids can be used for gluconeogenesis.