Glucose

Glucose is a six-carbon monosaccharide, or simple sugar, with the molecular formula C6H12O6. It is an aldohexose, and the naturally predominant form is D-glucose. Glucose circulates in the bloodstream and can be obtained from the digestion of dietary carbohydrates or produced within the body .^1,2

After entering cells, glucose is commonly phosphorylated to glucose-6-phosphate by hexokinase or, in certain tissues, glucokinase. Glucose-6-phosphate occupies a central position in metabolism and can enter several pathways. It can undergo glycolysis to produce pyruvate and capture energy as ATP and NADH, enter the pentose phosphate pathway, or be directed toward glycogen synthesis for storage .^2,3

Glycogen is a highly branched polymer of glucose and serves as a storage form of carbohydrate, particularly in the liver and skeletal muscle. When needed, glycogen can be broken down and its glucose-derived units returned to metabolic pathways. The body can also synthesize glucose from noncarbohydrate precursors through gluconeogenesis .^2,3

Glucose is chemically distinct from fructose even though both have the molecular formula C6H12O6. Their atoms are arranged differently, with glucose classified as an aldose and fructose as a ketose, and they differ in aspects of their transport and metabolism. Glucose is also distinct from sucrose, which is a disaccharide containing one glucose unit linked to one fructose unit .^1,2