1. Distinguish between channels and transporters.
2. What is a "ligand-gated channel"?  A "voltage-gated channel"?
3. Indicate the types of features that might determine the specificity of a channel for anions.
4. Explain the features of the bacterial K⁺ channel responsible for:
   1. Selectivity for cations rather than anions;
   2. Discrimination between K⁺ and Na⁺;   and
   3. Gating.
5. Explain the components of the "electrochemical gradient" as they affect:
   1. Net transport of an uncharged polar molecule into a cell whose membrane potential is "inside negative" (the usual situation);
   2. Net transport of a cationic molecule into a normal cell when the concentration of the molecule inside the cell is the same as its external concentration; and
   3. Net transport of an anionic molecule into a cell when the concentration of the molecule outside the cell is twice its concentration inside.
6. Distinguish among "active transport", "facilitated diffusion" ( = "mediated transport" = "passive transport") and "simple diffusion".
7. What is a "sodium pump"?
8. What is an "ABC transporter"?   Give a medically important example.
9. Relate the discrete steps in the action of the Na⁺+K⁺-ATPase to the coupling between movement of ions up their electrochemical potentials and energy release via ATP hydrolysis.
10. Why is it important that the enzyme reaction supplying energy for primary active transport is catalyzed by the same protein that performs the actual transport?
11. Compare "symports", "antiports", and "uniports".   Which can provide a mechanism for accumulation of a solute against its electrochemical potential, and which cannot?   Why?
12. What are the major ions involved as "fuel" for most secondary active transport systems? What feature makes them suited to this role?   Explain.
13. Explain the energetic principle that allows symports to cause the accumulation of an organic solute (such as glucose) against its concentration gradient.   Does this principle apply to antiports as well?   Explain.
14. What do we mean when we say a transport process is "electroneutral"?  Explain why an antiport driven by K⁺ efflux is most likely electroneutral.
15. Describe the transport systems responsible for the effective transfer of glucose from the mammalian intestinal lumen into the body fluids and indicate the factors that prevent loss of blood glucose to the gut lumen during periods of fasting.
16. Explain how inhibiting the Na⁺ + K⁺ - ATPase in the basolateral membranes of enterocytes would affect their ability to handle glucose effectively?   Be complete.
17. In laboratory experiments using RBCs, one can create conditions (altering the internal contents of ions, ADP, ATP, and phosphate) that will cause the Na⁺-K⁺-ATPase to run backwards as an ATP synthase.
    1. In what direction would the various ions involved move under these circumstances?
    2. What is the source of energy for ATP synthesis?
    3. What types of experimental alternations in ion levels would favor this situation?

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