Please see Question 2
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Homework Assignment #4
1.

Your friend has isolated plasma membranes and reassembled the membranes into
small vesicles. Using fluorescently labeled lectin, he sees that some of his vesicles
are fluorescently labeled and some are not. Recall that lectin binds to
carbohydrates. Furthermore, his labeled lectin cannot permeate membranes.
A.
Which population of vesicles has a surface similar to that of the cell?
Why?
B.
How do you explain the other population of vesicles?

2.

You have isolated a bacterial transporter that transports Mg2+ and Ca2+ in opposite
directions. You produce lipid vesicles that contain this Mg2+–Ca2+ pump as the
sole membrane protein. The Mg2+–Ca2+ pumps are oriented such that Mg2+ is
pumped into the vesicle while Ca2+ is pumped out. Each pump transports one
Mg2+ ion into the vesicle and one Ca2+ ion out of the vesicle during each pumping
cycle and ATP hydrolysis powers this transport, as illustrated in Figure below.

A.

Predict what would happen if the solution inside the vesicles contained 75
mM Mg2+ and 75 mM Ca2+ ions, while the solution outside the vesicles
contained 75 mM Mg2+ and 75 mM Ca2+ ions as well as 1 mM ATP, and
you had a 10,000 fold excess of fluid outside the vesicles compared with

B.

the volume inside the vesicles. Specifically, be sure to state whether you
think there would be net movement of ions and if so, how the
concentrations of the Mg2+ and Ca2+ ions inside and outside the bilayer
would change. In addition, be sure to state whether you would be creating
an electrical gradient, a chemical gradient, or both.
Explain how long the pump will run.