Problem 2. (20 points) You have prepared lipid vesicles that contain Nat - Kt pu

Question

Problem 2. (20 points) You have prepared lipid vesicles that contain Nat - Kt pumps as the sole membrane protein. Assume that each pump transports one Na+ one way and one K+ the other way each pumping cycle as shown in the figure below. All of the pumps are oriented so that the portion of the molecule that normally faces the cytosol faces the outside of the vesicle. Predict what would happen under the following conditions and explain each answer in a sentence or two A.) The solution inside and outside the vesicles contains both Na+ and K+ ions but no ATP. B.) The solution inside the vesicles contains both Na+ and K+ ions; the solution outside the vesicles contains both ions plus ATP C.) The solution inside contains Na+; the solution outside contains Nat plus ATP D.) The solution is the same as B but the pumps are randomly oriented some facing one direction, some facing the other ADP ATP Na* Na'

Explanation / Answer

A. The ATP provides energy for the Na+ - K+ pumps. In the absence of ATP, no ions will be pumped.

B. The pumps will use ATP hydrolysis to transport Na+ into the vesicle and K+ out, generating oppositely oriented concentration gradients of Na+ and K+ across the membrane. The pump will stop when the ATP runs out or when the K+ inside the vesicle is exhausted.

C. Under the given conditions, the pump will proceed through the first three steps as in the given figure and then stops because the conformational changes are strictly sequential, the subsequent steps cannot occur and so, the pumps will be stuck. Similar experiments leaving out individual ions and analyzing their consequesnces were used to determine the sequence of steps by which the Na+ - K+ pump works.

D. If the pumps were randomly oriented in the membrane, the result would be the same as in B. The pumps oriented with the ATP hydrolysis site exposed to the inside of the vesicle would be inactive because they would not have access to ATP.

Related Questions

Navigate

• Browse (All)
• Browse P
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.