SI session Oct. 11 Ch. 8 and 9 answers

SI session Oct. 11 Ch. 8 and 9 answers - Kaiser Imam...

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Kaiser Imam October 11, 2007 BIOL 215 SI Session Chapters 8 and 9 Chapter 8: Transport Processes 1. List 3 reasons why cells utilize active transport: 1) Aids in the uptake of nutrients from the environment or surrounding fluid 2) Allows wastes and other substances to be removed from the cell or organelle, even when the concentration outside is greater than that inside 3) Enables the cell to maintain constant nonequilibrium intracellular concentrations of certain ions even against their concentration gradient (ex: Na + , K + , Ca +2 , H + , Cl - ) 2. What is the difference between direct and indirect active transport? In direct active transport the movement of a solute molecule or ion is directly coupled to an exergonic chemical reaction such as the hydrolysis of ATP. Indirect active transport depends on the simultaneous transport of two solutes, with the movement of one solute down its gradient driving the movement of the other up its gradient. 3. Describe the following types of ATPases involved in active transport: a) P-Type ATPases: are reversibly phosphorylated by the phosphate molecule from ATP as part of the transport mechanism b) F-Type ATPases: generates H + gradient that drives ATP synthesis. The pumps essentially run in reverse and function as ATP synthases, producing ATP as well as consuming it. c) ABC-type ATPases: stands for “ATP binding cassette.” Found in some bacteria and can be used to pump drug molecules out of the cell. Also found in some tumors where they can be used to pump out chemotherapy drugs. 4. Explain the mechanism of the Na + /K + pump. The Na + /K + pump moves 3 Na + ions out of the cell and 2 K + inside. The protein starts in the E 1 conformation in which it is open to the inside of the cell and its sodium binding sites are available for binding. Three Na + ions bind to the protein, after which a molecule of ATP is hydrolyzed and the phosphate is attached to the pump. This causes a conformational change in the protein that leaves it open to the outside of the cell (E 2 conformation). The Na + ions then diffuse out and 2 K + ions can now bind to the pump. At this point the phosphate still attached to the protein is removed, causing a conformational change that leaves the pump open to the inside of the cell, allowing the K + to diffuse into the cell. The protein then reverts back to its initial E 1 conformation. 1
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5. Explain the mechanism of the Na + /Glucose symporter. The Na + /Glucose symporter initially starts with its binding sites open to the outside of the cell. First two Na + ions bind to the symporter, causing a conformational change that allows a molecule of glucose to bind to its site. This causes another conformational change that leaves the symporter open to the inside of the cell. Sodium and glucose are released into the inside of the cell. The Na + /Glucose symporter is an example of indirect active transport. It is powered by the movement of Na+ down its gradient (remember that the Na + gradient was set up by the Na
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SI session Oct. 11 Ch. 8 and 9 answers - Kaiser Imam...

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