In addition to amino acids, what other substrate can be used to make glucose from protein?

The correct answer, glycerol, is significant because it serves as an important precursor for gluconeogenesis, the metabolic pathway through which glucose is synthesized from non-carbohydrate sources. When proteins are broken down, the amino acids released can enter various metabolic pathways, and in some instances, they can be converted into glucose. Specifically, glycerol, which is derived from the breakdown of triglycerides (fats), can be converted into glucose in the liver.

This process is particularly crucial during periods of fasting or low carbohydrate intake when the body needs to maintain blood glucose levels. Since glycerol is a three-carbon molecule, it can be converted into glucose through gluconeogenesis, making it a direct contributor to the formation of glucose from non-carbohydrate sources.

The other options, while involved in energy metabolism, do not directly participate in gluconeogenesis in the same way. Fatty acids cannot be converted to glucose because they enter metabolic pathways that produce acetyl-CoA, which cannot be converted back into glucose. Cholesterol is a type of lipid that plays a role in membrane synthesis and hormone production but does not contribute to glucose synthesis. Lactate can be involved in gluconeogenesis, but it originates from glycogen or glucose metabolism rather than being a