Ion which promotes glucose absorption in the gut region: September 2007

Ans. C: Na+Glucose enters cells by facilitated diffusion or, in the intestine and kidneys, by secondary active transpo with Na+. In muscle, fat, and some other tissues, insulin facilitates glucose entry into cells by increasing the number of glucose transpoers in the cell membranes.The glucose transpoers that are responsible for facilitated diffusion of glucose across cell membranes are a family of closely related proteins that cross the cell membrane 12 times and have their amino and carboxyl terminals inside the cell. They differ from and have no homology with the sodium-dependent glucose transpoers, SGLT 1 and SGLT 2, responsible for the secondary active transpo of glucose out of the intestine, although the SGLTs also have 12 transmembrane domains. Paicularly in transmembrane helical segments 3, 5, 7, and 11, the amino acids of the facilitative transpoers appear to surround channels that glucose can enter. Presumably, conformation then changes and glucose is released inside the cell.