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  • The following complexes are found in the photosynthesis electron transport chain:

  • and the complex that makes ATP

  • In addition to the complexes,

  • three mobile carriers are also involved:

  • Other key components include:

  • and the electrons to form NADPH

  • which combine to form ATP

  • Photosynthesis occurs in the chloroplasts

  • of plants and algae.

  • The process is also found in single-cell organisms

  • such as cyanobacteria

  • that do not have chloroplasts.

  • Like its mitochondrial counterpart,

  • the chloroplast electron transport chain

  • consists of several protein complexes and mobile electron carriers.

  • First, a photon of light hits a chlorophyll molecule

  • surrounding the Photosystem II complex.

  • This creates resonance energy that is transferred through neighboring chlorophyll molecules.

  • When this energy reaches the reaction center embedded in photosystem II,

  • an electron is released.

  • The reaction center chlorophyll contains electrons that can be transferred when excited.

  • One photon is needed to excite each of the electrons in this chlorophyll.

  • Once excited, two electrons are transferred to plastoquinone Qb, the first mobile carrier.

  • In addition to the two electrons,

  • Qb also picks up two protons from the stroma.

  • The two electrons lost from photosystem II

  • are replaced by the splitting of water molecules.

  • Water splitting also releases hydrogen ions into the lumen.

  • This contributes to a hydrogen ion gradient

  • similar to the one created by mitochondrial electron transport.

  • After two water molecules have been split, one molecule of molecular oxygen is created.

  • Plastoquinone Qb then transfers the two electrons

  • to the cytochrome b6-f complex.

  • The two protons it picked up

  • are released into the lumen.

  • These transfers are coupled with the pumping of two more hydrogen ions into the lumen space

  • by cytochrome b6-f.

  • The electrons are next transferred to plastocyanin, another mobile carrier.

  • Next,

  • the electrons are transferred from plastocyanin

  • to the Photosystem I complex.

  • It is here that photons again energize each electron and propel their transfer to ferredoxin.

  • Ferredoxin then transfers the electrons

  • to the ferredoxin-NADP-reductase,

  • also known as FNR.

  • After two electrons are transfered to FNR,

  • NADPH is made by adding the two electrons

  • and a hydrogen ion to NADP+.

  • The gradient created by the electron transport chain

  • is utilized by ATP synthase

  • to create ATP from ADP and Pi.

  • This is similar to the way ATP is synthesized in the mitochondria.

  • ATP, NADPH, and molecular oxygen are the final, vital, products of photosynthesis.

The following complexes are found in the photosynthesis electron transport chain:


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B2 中上級

光合成(光反応 (Photosynthesis (Light Reactions))

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    wshuang999 に公開 2021 年 01 月 14 日