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The thylakoid membranes are sac-like structures with a lipid bilayer separating the interior compartment from the stroma. Enzymes of photosynthetic electron transport are integral membrane proteins. In the dark, hydrogen ions are relatively evenly distributed between the stroma (outside) and inner thylakoid space (inside). |
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In contrast to dark reactions, a pH gradient forms during light reactions. Integral membrane proteins pump protons (H+) across the thylakoid membrane during light-dependent electron transport. The concentration of protons can be nearly 1000 x higher inside the thylakoids than in the stroma. |
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