Question

Chloroplast membrane vesicles are equilibrated in a simple solution of pH 5‎ . The solution is then adjusted to pH 8‎ . Which of the following conclusions can be drawn from these experimental conditions?

- ATP will not be produced because there is no ADP and inorganic phosphate in the solution.
- ATP will be produced because the proton gradient favors proton movement through the ATP synthase channels.
- Protons will not diffuse toward the outside of the vesicles.
- The change in the solution's pH results in a gradient across the chloroplast membranes such that there is a lower concentration of protons inside the vesicles and a higher concentration outside.

Answer 1

ATP will not be produced because there is no ADP and inorganic phosphate in the solution.

Step-by-step explanation:

The thylakoid membranes of chloroplasts have ATP synthase embedded which in turn drives the phosphorylation of ADP into ATP. The process is driven by electrochemical gradient generated across the membrane by pumping the protons from stroma to thylakoid space during electron transfer. Therefore, the process of ATP synthesis in chloroplasts requires ATP synthase, ADP, inorganic phosphate and electrochemical gradient.

In the solution, the substrates ADP and inorganic phosphate are not added. In the absence of ADP and Pi, ATP synthase cannot drive photophosphorylation.