cell biology 4. You have isolated a bacterial transporter that transports Mg^2+

Question

cell biology 4. You have isolated a bacterial transporter that transports Mg^2+ and Ca^2+ In opposite directions. You produce lipid vesicles that contain this Mg^2+ - Ca^2+ pump as the sole membrane protein. The Mg^2+-Ca^2+ pumps are oriented such that Mg is pumped into the vesicle while Ca^2+ is pumped out. Each pump transports one Mg^2+ on into the vesicle and one Ca^2+ 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 Mg^2+ and 75 mM Ca^2+ ions, while the solution outside the vesicles contained 75 mM Mg^2+ and 75 mM Ca^2+ 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 Mg^2+ and Ca^2+ 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. 1 mM of ATP will transport 1 mM of Mg2+ into the vesicle and 1 mM of Ca2+ ion out of the vesicle. So the solution inside the vesicles would now contain 76mM Mg2+ and 74mM Ca2+ ions, while the solution outside the vesicles would contain 74mM Mg2+ and 76mM Ca2+ ions. There would be only chemical gradient of the individual ions and no electrical gradient. There won't be any electrical gradient as the total no. of ions inside and outside the bilayer would still be the same.

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