Exam 10: Membrane Structure

The nicotinic acetylcholine receptor is a cation channel in the plasma membrane of some neurons. It is composed of five subunits, each of which is a transmembrane protein. The hydropathy plot for each mature subunit is qualitatively represented in the following diagram. How many membrane-spanning alpha helices do you expect to exist in each subunit?

For each membrane protein in the following schematic drawings, indicate whether the cytoplasmic side of the membrane is more likely to be on the left (L) or on the right (R). Your answer would be a four-letter string composed of letters L and R only, e.g. RRRR.

The lateral diffusion of a plasma membrane protein has been studied using the fluorescence recovery after photobleaching (FRAP) technique in a cell under normal conditions, and the following plot has been obtained. Under a different condition (e.g. when a signaling pathway is turned on), the protein binds to a few other proteins and protein complexes in the plasma membrane. As a result, its lateral diffusion coefficient is reduced and a significant fraction of the molecules of this protein are immobilized in large aggregates. How would you expect the FRAP curve to change under these new conditions? The dotted line in each graph is the original curve shown for comparison.

Why do liposomes not fuse with one another spontaneously when suspended in an aqueous environment?

Which of the following changes would you expect to increase the phase transition temperature of a synthetic bilayer composed of phosphatidylserine?

While examining the crystal structure of a membrane protein, you find several phospholipid molecules bound to the protein. You know that these lipids …