Chapter 10: Q7CP (page 309)
Explain how and why ion channels are gated.
Short Answer
Ion channels are gated to open and close transiently to allow a certain number of ions to pass through them in response to a stimulus.
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Chapter 10: Q7CP (page 309)
Explain how and why ion channels are gated.
Ion channels are gated to open and close transiently to allow a certain number of ions to pass through them in response to a stimulus.
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What are the similarities and differences among ionophores, porins, ion channels, and passive-mediated transport proteins? What determines the direction of solute movement?
Give an example of a substance that can diffuse across a membrane. Give an example of a substance that must cross a membrane by mediated transport.
The bacterial Na+- H+ antiporter is a secondary active transport protein that excretes excess Na+ from the cell. Is the extracellular pH higher or lower than the intracellular pH?
Cells in the wall of the mammalian stomach secrete HCI at a concentration of 0.15 M. The secreted protons, which are derived from the intracellular hydration of by carbonic anhydrase, are pumped out by an antiport. A co-transporter is also required to complete the overall transport process.
a) Calculate the pH of the secreted HCl. How does this compare to the cytosolic pH (7.4)?
b) Write the reaction catalyzed by carbonic anhydrase.
c) Draw a diagram to show how the action of both transport proteins results in the secretion of HCI.
E. coli cells transport xylose across the cell membrane via a symport system that uses the free energy of a proton gradient. The intracellular pH is higher than the extracellular pH. (a) Is xylose moving up or down its concentration gradient? Into or out of the cell? (b) Draw a diagram of the xylose transport system.
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