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12 Cards in this Set
- Front
- Back
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How does glucose enter cells?
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By facilitated diffusion. In the intestines and kidneys, by 2ary active transport with Na+.
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How does glucose enter muscle, fat and some other tissues?
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Insulin facilitates glucose entry into cells by increasing the number of glucose transporters in the cell membranes.
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How would one describe the glucose transporters that are responsible for facilitated diffusion of glucoe across cell membranes?
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They are a family of closely related proteins that cross the cell membrane 12 times and have their amino and carboxyl terminals inside the cell.
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How do the above transporters differ from the Na+ dependent glucose transporters?
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They differ from and have no homology with the sodium dependent glucose transporters, SGLT1 and SGLT2 responsible for the 2ary active transport of glucose out of the intestine and renal tubules, although the SGLTs also have 12 transmembrane domains.
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How many glucose transporters have been recognized?
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Seven different glucose transporters, referred to in order of discovery, GLUT-1-7 have been characterized? They contain 492-524 amino acid residues, and their affinity for glucose varies.
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GLUT-4 is the transporter in muscle and adipose tissue that is stimulated by insulin. TRUE/FALSE
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TRUE. A pool of GLUT-4 molecules is maintained in vesicles in the cytoplasm of insulin sensitive cells.
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What happens when the above receptors are activated?
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The vesicles move rapidly to the cell membrane and fuse with it, inserting the transporters into the cell membranes.
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What happens in the above cases, when insulin action ceases?
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The transporter containing patches of membrane are endocytosed, and the vesicles are ready for the next exposure to insulin.
Activation of the insulin receptor brings about the movement of the vesicles to the cell membrane by activating phosphoinositol-3-kinase. |
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In the tissues in which insulin increases the number of glucose transporters in the cell membrane, the rate of phosphorylation of the glucose, once it has entered the cells, is regulated by other hormones. TRUE/FALSE
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TRUE. GH and cortisol both inhibit phosphorylation in certain tissues
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What can be said about how insulin increases the entry of glucose into liver cells?
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This statement is true, but it does not exert this effect by increasing the number of GLUT-4 transporters in the cell membranes.
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In reference to the correct answer above, how then does the process continue?
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It induces glycokinase and this increases the phosphorylation of glucose, so that the intracellular free glucose concentration stays low, facilitating the entry of glucose in the cell.
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Insulin sensitive tissues also have a population of GLUT 4 vesicles that move into the cell membrane in response to exercise and are independent of the action of insulin. TRUE/FALSE
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TRUE. Itb is believed that this is the reason why exercise lowers blood sugar.
A 5' AMP activated kinase may be responsible for the insertion of these vesicles in the cell membrane. |
