Fatty acids from stored triacylglycerols (fat) are not available for gluconeogenesis. Speculate why we do not have the enzymes to directly convert fatty acids into glucose. Plants (especially seeds) do have enzymes to convert fatty acids into carbohydrates. Why are they so lucky?

Gluconeogenesis is the metabolic pathway that generates glucose from non-carbohydrate substrates, primarily occurring in the liver and kidneys. This process is crucial for maintaining blood glucose levels during fasting or intense exercise. It primarily utilizes precursors like lactate, glycerol, and certain amino acids, but not fatty acids, which lack the necessary carbon skeleton for glucose synthesis.

Fatty acid metabolism involves the breakdown of fatty acids for energy through processes like beta-oxidation, which converts fatty acids into acetyl-CoA. This acetyl-CoA can enter the citric acid cycle for energy production but cannot be converted back into glucose in animals. This limitation is due to the irreversible nature of certain steps in the citric acid cycle, which prevents the conversion of acetyl-CoA into glucose.

Plants, particularly seeds, possess the glyoxylate cycle, a metabolic pathway that allows them to convert fatty acids into carbohydrates. This cycle bypasses the decarboxylation steps of the citric acid cycle, enabling the conversion of acetyl-CoA into four-carbon compounds that can be further processed into glucose. This adaptation is essential for seed germination, providing energy and carbon sources when photosynthesis is not yet possible.