Glycogen contains many glucose monomers.

• A. Fructose
• B. Galactose
• C. Glucose
• D. Ribose

Answer: (C)

Glycogen is a storage polysaccharide in animals built from repeating glucose units. The glucose molecules are linked together to form a highly branched polymer, with most linkages being α-1,4 and branches created by α-1,6 bonds. Because glycogen is specifically composed of glucose units, the monomer that makes up glycogen is glucose.

Fructose, galactose, and ribose are different sugars with distinct structures and roles. Ribose is the sugar in RNA (and DNA’s backbone uses a related deoxyribose), while fructose and galactose are alternative hexoses that do not form the glycogen polymer themselves, even though they can be metabolically interconverted. The unique composition of glycogen as a glucose polymer is what ties its function to rapid energy storage and mobilization in animals.