Glucose/Sugar Transport in Mammals

Glucose is the primary energy source for mammalian cells and its oxidation provides adenosine triphosphate under both anaerobic and aerobic conditions. Moreover, its storage as glycogen in the liver provides a ready source of glucose during states of fasting through the catabolism of glycogen and the release of glucose back into the circulation. Glycogen storage also represents the primary source of energy for muscle. In adipocytes, glucose can be converted to triglycerides, a more energetically compact fuel store that can be better metabolized to fatty acids and glycerol. Apart from being a major source of metabolic energy, glucose is also a source of structural moieties for other macromolecules including glycoproteins, proteoglycans, glycolipids, and nucleic acids. However, glucose is a highly polar molecule that is impermeable across cell membrane and therefore two specific families of mammalian glucose transporters, the sodium-dependent glucose transporters and the facilitative glucose transporters have evolved.