Final answer:
Glucose can be synthesized from lactate, pyruvate, glycerol, and galactose through gluconeogenesis, but not from fructose, which is directly absorbed during digestion.
Step-by-step explanation:
The substances from which glucose can be synthesized are lactate, pyruvate, glycerol, and galactose, but not fructose. Fructose is a monosaccharide like glucose and they both are isomers, meaning they share the same chemical formula (C6H12O6), but their structures and chemical properties differ due to varied arrangements of atoms.
Under conditions like fasting or low-carbohydrate diets, the body can create glucose through a process known as gluconeogenesis, but it doesn't utilize fructose as a substrate.
Instead, fructose is absorbed directly into the bloodstream during digestion and shares the same caloric value as glucose, without being a direct precursor in gluconeogenesis.
Glucose can be made from lactate, glycerol, pyruvate, and fructose. However, it cannot be made from galactose. Glucose and galactose combine to form lactose, which is a disaccharide composed of both glucose and galactose molecules.