GLUT4 glucose transporter

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Glucose and fructose are the major energy and carbon sources for organisms like human beings and yeast. These organisms can derive the other monosaccharides required for glycan(which refers to the assembly of sugars either in free or in attached form) bio-synthesis from these sources.


The generalised form of this reaction is written as follows
There are three types of sugar transporters that carry sugars across the plasma membrane in to the cells. First are the energy independent facilitated diffusion transporters such as the glucose transporters family(GLUT) of hexose transporters seen in yeast and in mammalian cells. These proteins are encoded by SLC2A genes(solute carriers 2A). Second are the energy dependent transporters for example sodium dependent glucose transporters(SGLT) encoded by SLC5A genes in the intestine and in kidney epithelial cells. The third type of transporters couple ATP dependent phosphorylation with sugar import and are seen in bacteria.
This family of glucose transporters were first discovered in yeast where 18 genes have been identified. Humans have 14 GLUT homologs. All of the yeast glucose transporters are of the same size(40-55 Kilodaltons) and have similar structures containing 12 membrane spanning domains. These domains form a barrel with a small pore for the sugar to pass through. The only "sugar transport signatures" are a few widely scattered glycine and tryptophan residues and one PET tri-peptide sequence
The elevated levels of blood sugar and amino acids that occur following a meal signal pancreatic beta cells to release insulin into the bloodstream. ...
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