Glucose transporters

Carbohydrates exist as polysaccharides (such as starch), disaccharides (such as sucrose, maltose and lactose) and monosaccharides (such as galactose, glucose and fructose). Glucose absorbed from the gut is mainly derived from starch that, in Western societies, constitutes about 60% of the daily carbohydrate intake. The rest is in the form of sucrose (30%) and lactose (10%). In starch, straight chains of glucose molecules are held in amylose (approximately 20% of the total starch) whilst branched chains of glucose molecules are held in amylopectin (80% of the total starch). In the gut, these large molecules are broken down by digestion but the polarity of the hexoses sugars requires specialized transport proteins that will facilitate absorption across the hydrophobic cell membrane of the gut. There are five of these glucose transporters (GLUTs) for the absorption and uptake of glucose into cells. These have distinct tissue distributions and features.