Biochemistry/Electron Transport Chain

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The electron transport chain is used in both photosynthesis as well as in cellular respiration. In photosynthesis, when sunlight is absorbed in photosystem 2, electrons are energized. They are transferred to the reaction center. From the raction center, the electrons enter the electron transport chain and pass the etransport chain molecules. Then the 2 deenergized electrons are reenergized in Photosystem 1 (is second because PSII was discovered first)and they go to the NAPD+ reductase which transfers ther electrons to a coenzyme, converting it to NADPH+ The two electrons used must be replaced, so water is broken down producing 2 protons (H+) which concentrate in the thylakoid membrane, 2 electrons replaced in PSII and oxygen released as O2. Protons go down proton pumps and a concentration gradient forms as protons move from the stroma into the thylakoid space. Protons move down gradient through ATP synthase which forms ATP. Energy is stored.