Supplemental Questions forMembrane Transport
1. Most cells have intracellular Na+ concentrations of 12 mM, compared to the extracellular concentration of 140 mM.
a. Calculate the Gibb's free energy change for the flow of Na+ from the inside of the cell to the outside, for a cell with a membrane potential of 50 mV (negative on the inside).
b. Is energy required for this process to occur?
c. If energy is given off, suggest a potential use for this energy. If energy is required, suggest a potential source of energy.
2. It has been postulated that the risk of coronary heart disease may be diminished by consuming a diet that is high in 3 fatty acids (they have a double bond that starts three carbons from the end of the long chain.) Fish from very deep water is an excellent source of these fatty acids. Explain why a deep water fish would have a high concentration of unsaturated fatty acids.
3. Red blood cells have an antiport exchanger for bicarbonate and chloride ions. A diagram of RBCs in the lung and in the tissue is shown below.
a. Fill in the dotted blanks at the end of each arrow to show what goes into and out of the cell in the tissues and in the lungs.
b. Why is this system necessary?
c. Does this transporter require energy? Explain your answer.
4. Red blood cells have a glucose permease that transports glucose into the cells via passive transport. Intestinal cells have a secondary active transport system that allows glucose concentrations to accumulate in these cells.
a. Why is a permease or transport system required to get glucose into a cell?
b. Why would red blood cells have a passive system and intestinal cells require a secondary active system?
