Question

You are testing the rate of glucose transport into vesicles using a Na^+-glucose pump. This transporter protein transports Na^+ and glucose in the same direction, and is a coupled transporter such that binding of cither Na^+ or glucose increases the affinity of the transporter to bind the other solute. In experiment 1, you create artificial vesicles that have the Na^+-glucose pump in the membrane. These vesicles have glucose but no Na^+ ions inside. You place these vesicles into a series of tubes containing the same glucose concentration as i the inside of the vesicle. These tubes vary in their Na^+ concentration, with 0, 1, 2, 3, or 10 mM Na^+. Your results from your measurements of the initial rates of glucose transport into the vesicles with the varying concentrations of Na^+ are on the graph (see experiment 1). Explain why glucose is not being transported when there is no Na^+ in the external solution. Explain why the initial rate of glucose transport into the vesicle plateaus as the concentration of Na^+ increases.

Answer 1

Ans: i) Na⁺ play the role of coupled transport protein. When sodium goes inside the vesicle then it co- transport glucose inside the vesicle.

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ii) Initial concentration of Na⁺ is high outside the vesicle. Because Na⁺ is a coupled tranport protein then it transport glucose inside the cell. After sometime concentration of Na⁺ become equal on both side(Outside and inside of vesicle). Vesicle become isotonic for Na⁺ ions. Then glucose is not transported inside the cell . So glucose transport into the vesicle plateaus as the concentration of vesicle become Na⁺ increases.