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A proton gradient is created across the thylakoid membrane (6) as protons (3) are transported from the chloroplast stroma (4) to the thylakoid lumen (5). Through chemiosmosis, ATP (9) is produced where ATP synthase (1) binds an inorganic phosphate group (8) to an ADP molecule (7).
The proton gradient can be generated through either noncyclic or cyclic photophosphorylation. Of the proteins that participate in noncyclic photophosphorylation, photosystem II (PSII), plastiquinone, and cytochrome b 6 f complex directly contribute to generating the proton gradient. For each four photons absorbed by PSII, eight protons are ...
Chemiosmosis is the movement of ions across a semipermeable membrane bound structure, down their electrochemical gradient.An important example is the formation of adenosine triphosphate (ATP) by the movement of hydrogen ions (H +) across a membrane during cellular respiration or photosynthesis.
In photophosphorylation, light energy is used to pump protons across a biological membrane, mediated by flow of electrons through an electron transport chain. This stores energy in a proton gradient. As the protons flow back through an enzyme called ATP synthase, ATP is generated from ADP and inorganic
In addition, this creates a proton gradient (energy gradient) across the chloroplast membrane, which is used by ATP synthase in the synthesis of ATP. The chlorophyll molecule ultimately regains the electron it lost when a water molecule is split in a process called photolysis, which releases oxygen.
By replenishing lost electrons with electrons from the splitting of water, photosystem II provides the electrons for all of photosynthesis to occur. The hydrogen ions (protons) generated by the oxidation of water help to create a proton gradient that is used by ATP synthase to generate ATP.
The carriers in the electron transport chain use some of the electron's energy to actively transport protons from the stroma to the lumen. During photosynthesis, the lumen becomes acidic, as low as pH 4, compared to pH 8 in the stroma. [30] This represents a 10,000 fold concentration gradient for protons across the thylakoid membrane.
The combined transmembrane gradient of protons and charges created by proton pumps is called an electrochemical gradient. An electrochemical gradient represents a store of energy (potential energy) that can be used to drive a multitude of biological processes such as ATP synthesis, nutrient uptake and action potential formation. [citation needed]