Answer to in-class problems

Answer to in-class - remain low and no leucine will bind the transporter 2 If the transporter protein had a mutation that caused it to have a very

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Answers to Membranes ICP on Secondary Active Transport Most mammalian cells maintain an electrochemical gradient of sodium ions (Na + ) across their plasma membrane by means of an ATP-driven sodium pump. This gradient can be used to drive the uptake of molecules such as sugars or amino acids by specific transport proteins that couple the inward movement of Na + ions to the inward transport of the molecule of interest. 1) The amino acid leucine is brought into the cell via a cotransport mechanism with Na + . If the transporter protein had a mutation that abolished its ability to bind Na + , would that affect the movement of leucine into the cell? Why or why not? Be specific. It would prevent the entry of leucine into the cell. The binding of leucine to the cotransporter is dependent on the binding of Na + . The cotransporter’s affinity for leucine is low until Na + binds and changes the conformation into a high affinity for leucine. If Na + cannot bind, the affinity for leucine will
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Unformatted text preview: remain low and no leucine will bind the transporter. 2) If the transporter protein had a mutation that caused it to have a very high affinity for Na + (essentially permanent binding), would that affect the movement of leucine into the cell? Why or why not? Be specific. This mutation would also abolish the transport of leucine into the cell. Normally, the Na + is released from the cotransporter into the cytoplasm because the [Na + ] is so much lower inside the cell than outside. This release of Na + normally lowers the affinity of the cotransporter for leucine so low that the leucine is dropped off even though the surrounding leucine concentration is high. If the mutation causes the Na + to remain bound even when the cotransporter faces the cytoplasm, the leucine will not be able to release. Thus, the Na + and the leucine remain stuck in the cotransporter and no overall transport of either solute occurs....
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This note was uploaded on 10/16/2008 for the course BIO 315 taught by Professor Howard during the Fall '08 term at Wisc La Crosse.

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