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foodjunkie foodjunkie
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11 years ago
What happens in a thylakoid membrane in a choroplast?
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#1
11 years ago
The thylakoid as you may know is the disk-shaped organelle inside the chloroplast. The membrane itself is  the site where light-dependent photosynthetic reactions take place. These are the reactions that initially excite the electrons so they fall down the electron transport chain and release ATP and continue on to release NADPH.

If you are familiar with Photosystems I and II, both of these take are present in the thylakoid membrane and process the light-dependent reactions.
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11 years ago
The thylakoid membrane of the chloroplast is the site of the light-dependent reactions of photosynthesis.  There, the chlorophylls of photosystems I and II absorb incident photons in their antenna complexes, and the energy of those photons is directed to the reaction center chlorophylls of the photosystems.  In photosystem II, one of the electrons of the P680 reaction center chlorophyll is transferred out of the photosystem to plastoquinone, which in turn reduces the cytochrome b6-f complex that transfers electrons with the concomitant transfer of protons, via a Q cycle, into the thylakoid lumen.  Cytochrome b6-f then transfers the electrons to plastocyanin, which in turn regenerates the photooxidized P700 reaction center chlorophyll of photosystem I.  The electron ejected from P700, through the intermediacy of a chain of electron carriers, reduces NADP+ to NADPH in noncyclic electron transport.  Alternatively, the electron may be returned to the cytochrome b6-f complex in a cyclic process that only translates protons into the thylakoid lumen.  In photosystem II, protons are split off from water by the oxygen-evolving complex, yielding O2.  The resulting H+ gradient powers the synthesis of ATP by the CF1CF0 proton-translocating ATP synthase.  Of course, the ATP and NADPH created in the light-dependent reactions will power the subsequent light-independent reactions (Calvin cycle) in the stroma of the chloroplast.
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