14-CO2 was bubbled through a suspension of liver cells that was undergoing gluconeogenesis from lactate to glucose. Which carbons in the glucose molecule synthesized would become radioactive?

A metabolic process known as gluconeogenesis refers to an enzyme-catalyzed reaction, which takes place in kidneys or liver. The process results in the generation of glucose from the non-carbohydrate precursors like glycerol or lactate.

In the process of gluconeogenesis, carbon dioxide gets discharged during the formation of phosphoenolpyruvate from oxaloacetate. As there is a discharging of carbon dioxide taking place in the reaction, and no external carbon dioxide is needed for the formation of glucose from lactate, therefore, none of the molecules of glucose will be radioactive.