You have isolated a bacterial transporter that transports Mg2+ and Ca2+ in oppos

Question

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 4. 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 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.

Explanation / Answer

There would be net movement of ions. Active transporters, or ones using energy, do not depend on chemical or electrical gradients, only on the presence of chemicals being transported, and ATP. Since there is ATP, the transporter can function. Magnesium ion concentration would be higher inside the vesicle, and calcium concentration would be higher outside the vesicle.

An electrical would not be created, since the electrical charge on both magnesium and calcium ions are equal, and since the transportation is one ion to one, the net electrical change does not change.

However, a chemical gradient is being created. Concentrations of both chemicals are changing, so that the concentration will be higher on one side, and lower on the other. These kinds of gradients are used in transportation of other chemicals, called secondary active transport.

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