You are told that the structure of a channel that allows protons to cross the bacterial membrane has 12 amphipathic α -helices.

3 a. Describe the orientation of these helices with respect to the plane of the membrane. (1 sentence)

The 12 Helices will be oriented

3 b. Describe how both the polar sidechains and the nonpolar sidechains within the helices are arranged within the protein structure. (2 sentences or less)

3 c. The function of this protein is to move protons through a water-filled cavity between the 12 helices. Which two of the following amino acid side chains would be most likely to line this water-filled channel? (Circle the correct ones).

Ser                              Gln                               Met                              Trp

3 d. If the pH of the cell cytoplasm is 8.0 and the pH of the extracellular medium is 6.5, what do you expect the thermodynamically favorable direction of proton transfer to be?