Question

1.

a. Cells must maintain an appropriate level of fluidity across their membranes. Hot
temperatures lead to greater membrane fluidity. What might you then expect to find
regarding the membrane composition of bacteria from very hot environments?

b.You have a cell with a fluorescently labeled lipid in equal abundance on the inner and outer
leaflets of the cell membrane. You then photobleach an area of membrane of this cell. What
will happen next to the bleached area?

c. Phospholipid vesicles are made with two secondary transporters in their lipid bilayers: a
sodium/calcium symporter and a sodium/potassium antiporter. The solution on the interior
of the vesicles contains 100 mM NaCl and 50 mM CaCl2. The vesicles are then placed in a
solution containing 50 mM NaCl and 50 mM KCl. What will be the initial flow of ions into
or out of these vesicles?

d. Grb-2 is a key adaptor protein in EGF signaling. What is the function of Grb-2 in EGF
signaling?

e. What are the general properties of trimeric G-proteins? Of monomeric G-proteins?

Answer 1

1.

a. An increased proportion of saturated fatty acids.

b. Steady rate of recovery starting at the edges of the photobleached area and moving inwards due to diffusion of the unbleached lipids into the bleached area.

c. Calcium will be transported out and potassium will be transported in.

d. Grb-2 recruits Sos which lead to Ras activation.

e. G-proteins are proteins that bind GTP or GDP. Trimeric G-protein has receptor, activated by the receptor ligand-binding, has three subunits that dissociate when activated, always bound to the membrane. Monomeric G-protein has no receptor, activated by GEF, fatty acid tail only binds to membrane when active, inactivated by GAP (controls GTP hydrolysis).