Question

The following diagram represents an experiment with isolated thylakoids. The thylakoids were first made acidic by soaking them in a solution at pH 4. After the thylakoid space reached pH 4, the thylakoids were transferred to a basic solution at pH 8. The thylakoids then made ATP in the dark. (See Concept 3.3 to review pH.).

Draw an enlargement of part of the thylakoid membrane in the beaker with the solution at pH 8. Draw ATP synthase. Label the areas of high H+ concentration and low H+ concentration. Show the direction protons flow through the enzyme and show the reaction where ATP is synthesized. Would ATP end up in the thylakoid or outside of it? Explain why the thylakoids in the experiment were able to make ATP in the dark.

Short answer

The flow of protons from the lumen to the outer stroma is shown in the given figure. The ATP synthase is represented below:

Researchers have provided an artificial set of protons; therefore, thylakoids are able to produce ATP in dark conditions

Step-by-step solution

Electrochemical proton gradient

At the time of transfer of the electron in the photosynthesis process, energy molecules are released in the stroma of the chloroplast.Electrochemical proton gradient refers to the proton motive force to help in the production of ATP molecules.

Photosystem I and photosystem II are located on the membrane of thylakoids, and photosystem II helps in the splitting of the water molecule that makes the lumen side rich with protons.

The pH of the thylakoid decreases, and the protons move to the stroma side to develop ATPs

Flow of protons through enzyme ATPase

The enzyme ATPase includes an F₁ head and F₀ base that is embedded in the membrane of the thylakoid and works as a proton channel. The F1 head protrudes in the stroma and has an active part of ATPase. This enzyme is involved in the formation of ATP.

The direction of flow of the protons is from the lumen to the stroma region. ATP synthase enzyme assists in the movement of hydrogen ions from higher to lower concentrations of protons. The ATP molecule is synthesized by the ATPase enzyme.

Formation of ATP in the dark reaction according to experiment

With the absence of light, thylakoids are able to make ATP molecules because the researchers have provided the artificial set for proton concentration across the membrane of the thylakoid. Therefore, the light reaction is not vital to form protons with the help of ATPase.