How is a proton gradient generated in photosynthesis?

Question

It says in a diagram I was given that pasage of electrons down the transport chain drives protons to the thylakoid interior, generating a proton gradient. How does it do this? And how does the dissipation of the transport gradient drive ATP synthesis??

Answer 1

Protons = Hydrogen Ions = H+



A proton is created as the hydrogen atoms from water (H2O) essentially becomes oxidized (electrons removed for the electron transport chan). The proton is then bushed into the thylakoid; the outside will have none. It is a "gradient" because there are a lot of hydrogens on one side and none on the other.



The gradient is dissipated as hydrogen ions move back outside of the thylakoid. This movement is "natural" according to the laws of science, as things in high concentration -> low concentration. As it flows back out, there are proteins on the thylakoid membrane that the protons pass through. Because this movement is "natural", it occurs with some substantial amount of energy; the protein captures this energy by coupling it with a reaction to make ADP+P -> ATP. Viola!

Answer 2

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RE:

How is a proton gradient generated in photosynthesis?

It says in a diagram I was given that pasage of electrons down the transport chain drives protons to the thylakoid interior, generating a proton gradient. How does it do this? And how does the dissipation of the transport gradient drive ATP synthesis??

Answer 3

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Chemiosmosis in Chloroplasts The energy released as electrons pass down the gradient between photosystem II and plastocyanin (PC) is harnessed by the cytochrome b6/f complex to pump protons (H+) against their concentration gradient from the stroma of the chloroplast into the interior of the thylakoid (an example of active transport). As their concentration increases inside (which is the same as saying that the pH of the interior decreases), a strong diffusion gradient is set up. The only exit for these protons is through the ATP synthase complex. As in mitochondria, the energy released as these protons flow down their gradient is harnessed to the synthesis of ATP. The process is called chemiosmosis and is an example of facilitated diffusion