What are the similarities and differences between photophosphorylation and oxidative phosphorylation?

Both processes operate on the same basic principle; passing electrons down a chain in order to create a proton (H+) gradient, allowing the formation of ATP. The biggest difference is where they occur. Photophosphorylation occurs in the thylakoid membrane of chloroplasts during the light-dependent stage of photosynthesis. Light in the form of photons supplies the energy needed to excite two e- s in PSII (photosystem II), which are then passed along the transport chain. Oxidative phosphorylation occurs in the membrane of mitochondrial christae during cellular respiration. Here, the e-s are supplied by NAD and FAD, with oxygen acting as the last electron acceptor, leading to the formation of H2O. During photophosphorylation, NADP acts as the last e- acceptor , leading to the formation of NADPH.

In both processes e-s are passed down a chain of electron transfer agents in a series of redox reactions. In both reactions, as e-s are passed along the cytochrome complex, H+ ions are pumped from an area of low to high concentration, creating a proton gradient. During photophosphorylation e-s are pumped from the stroma into the thylakoid, while in oxidative phosphorylation e-s are pumped from the matrix into the intermembranal space. The chemiosmosis of H+ ions down the concentration gradient through the pores of ATPsynthase then supplies the energy needed to phosphorylate ADP into ATP, which is the primary "energy carrier" in cells.

Answered by Gloria M. Biology tutor

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