Week 6 Review Sheet answers

Week 6 Review Sheet answers - Final Review Sheet Week 6...

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Final Review Sheet – Week 6 Lecture 14 Active Transport Main Points Active transport. The classic example is the sodium potassium ATPase, which pumps sodium ions out of a cell and potassium in, both against their concentration gradients. It uses the energy of one ATP per three sodiums, two potassiums. The model for the mechanism of NKA suggests that the change between a conformation open to the inside of the cell to one open to the outside is the result of phosphorylation of the protein (with the phosphate coming from ATP hydrolysis). Because of this, NKA is classified as a P-type ATPase. NKA can be inhibited by digitalis, ouabain, or by inhibitors of ATP production. In addition to the Na, K ATPase, the general class of P type ATPases includes the H + /K + ATPase in the stomach wall, which pumps protons into the stomach cavity. Some medications for heartburn work by blocking this enzyme. Two other major classes of transporters are V- type and ABC transporters. The V-type use ATP, but the transporter is not phosphorylated as an intermediate step. Secondary active transport involves movement of solutes without the direct use of ATP because the concentration gradients of one substance are used as an energy source. Recall that if a molecule moves with it concentration gradient, that movement represents a release of free energy. In secondary transport, movement of one substance with its concentration gradient provides the energy to move another against its gradient. In this type of movement the two materials may move in the same direction (symport) or in opposite directions (antiport). An example of symport is the glucose/Na + transporter in the intestinal epithelial cell. These molecules allow the cell to pick up glucose from the intestinal lumen and move it into the cell. Facilitated transporters on the other side allow the glucose to exit when the concentration of glucose is lower in the cell than in the blood. This type of cell does not automatically convert glucose to glucose-6- phosphate. An example of antiport is the Ca ++ /Na + system in cardiac cell membranes that pumps Ca++ out of cells after a contraction. This is another case in which the energy released by sodium ions traveling with their concentration gradient provides the energy to pump another ion against its concentration gradient. Here, Ca ++ concentration is higher outside the cell than in, but the sodium movement is sufficient to move the Ca ++ inns. The sodium and calcium move in opposite directions A number of diseases are associated with defects in ion channels or pumps. One of these is cystic fibrosis, which is based on a defect in a member of the ABS transporter superfamily. There are a number of different mutations seen in the human population in different CF patients. All have defects in this protein, but they may have varying symptoms based to some degree on the mutation they carry. The Human Perspective section of the chapter discusses this disease and potential
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Week 6 Review Sheet answers - Final Review Sheet Week 6...

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