Question

Imagine biologists engineer a protein in the thylakoid membrane of chloroplasts that allows protons (H⁺)to pass through it.

a. What is the proton (H⁺) gradient across the thylakoid membrane typically used for?
b. In cells with the engineered protein channel that allows protons (H⁺) to cross the thylakoid membrane, both the light reactions and the Calvin cycle eventually stop. Explain three reasons why photosynthesis cannot continue in these cells.

Answer 1

The proton gradient across the thylakoid membrane is used for ATP production through chemiosmosis. Introduction of protein channels that allow free proton flow disrupts this gradient, leading to a stop in ATP and NADPH production, and ultimately halting photosynthesis.

Step-by-step explanation:

The proton (H+) gradient across the thylakoid membrane in chloroplasts is typically used for producing ATP via a process known as chemiosmosis. This gradient is crucial for the light reactions of photosynthesis, which drive the production of ATP and NADPH, the energy carriers used in the Calvin cycle to synthesize glucose. If engineered protein channels allow protons to pass freely through the thylakoid membrane, it disrupts this gradient, leading to several issues:

• ATP Production Ceases: Because the proton motive force is dissipated, ATP synthase cannot use the energy from the flow of protons to convert ADP to ATP, resulting in energy depletion.
• Disrupted NADPH Formation: Without the energy to drive the electron transport chain, the necessary electrons and protons to reduce NADP+ to NADPH are not provided, halting a critical step in photosynthesis.
• Overall Photosynthesis Stops: Without ATP and NADPH, the Calvin cycle cannot proceed, leading to the cessation of glucose synthesis and overall photosynthesis.