AP Syllabus focus:
‘Electron transfer through the thylakoid electron transport chain creates a proton gradient across the thylakoid membrane.’
Electron transport in chloroplast thylakoid membranes converts light-driven electron movement into a transmembrane proton (H⁺) gradient. This gradient stores potential energy by separating charge and pH between the thylakoid lumen and stroma.
Practice Questions
FAQ
It uses plastoquinone/plastoquinol chemistry to move more H⁺ into the lumen per pair of electrons.
This can increase the H⁺ gain beyond simple electron hand-offs between carriers.
Researchers can track pH-sensitive dyes or observe electrochromic shifts in thylakoid pigments.
These signals change as membrane potential and lumenal acidity change.
Counter-ion movements (e.g., $Cl^-$ flux) and buffering in the lumen can reduce excessive charge separation.
This allows a strong $\Delta pH$ to persist.
Greater H⁺ permeability dissipates the gradient, so less energy is stored as a proton difference.
Electron transfer may continue, but the gradient-dependent energy capture is reduced.
It routes electrons back to the PQ/cytochrome b6f segment, increasing H⁺ accumulation via b6f without producing NADPH.
This can steepen the gradient when extra proton-driving force is needed.
