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Fotosintesis
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Mecanismo de Fotosíntesis
The process of photosynthesis produces ATP from ADP and PI by using the energy from light
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to excite electrons that are passed along an electron transport chain.
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Coupled with the transfer of electrons is the pumping of hydrogen ions and the splitting
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of water molecules.
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The following complexes are found in the photosynthesis electron transport chain.
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Photosystem II, Cytochrome B6F, Photosystem I,
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Ferredoxin NADP reductase, and the complex that makes ATP,
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ATP synthase.
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In addition to the complexes, three mobile carriers
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are also involved, Plastiquinone QB, Plastocyanin,
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and ferredoxin.
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Other key components include photons, chlorophyll molecules,
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protons, water, molecular oxygen, NADP and the electrons
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to form NADPH, and ADP and PI, which combine to form ATP.
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Photosynthesis occurs in the chloroplasts of plants
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and algae.
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The process is also found in single-cell organisms, such as cyanobacteria, that do not have chloroplasts.
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Like its mitochondrial counterpart, the chloroplast electron transport chain consists of several protein complexes and mobile electron carriers.
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First, a photon of light hits a chlorophyll molecule surrounding the photosystem II complex.
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This creates resonance energy that is transferred through neighboring chlorophyll molecules.
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When this energy reaches the reaction center embedded in photosystem II, an electron is released.
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The reaction center chlorophyll contains electrons that can be transferred when excited.
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One photon is needed to excite each of the electrons in this chlorophyll.
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Once excited, two electrons are transferred to plastiquinone QB, the first mobile carrier.
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In addition to the two electrons, QB also picks up two protons from the stroma.
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The two electrons lost from photosystem II are replaced by the splitting of water molecules.
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Water splitting also releases hydrogen ions into the lumen. This contributes to a hydrogen ion
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gradient similar to the one created by mitochondrial electron transport.
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After two water molecules have been split, one molecule of molecular oxygen is created.
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Plastiquinone QB then transfers the two electrons to the cytochrome B6F complex.
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The two protons it picked up are released into the lumen.
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These transfers are coupled with the pumping of two more hydrogen ions into the lumen space by cytochrome B6F.
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The electrons are next transferred to plastocyanin.
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another mobile carrier.
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Next, the electrons are transferred from plastocyanin
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to the photosystem I complex.
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It is here that photons again energize each electron
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and propel their transfer to ferredoxin.
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Ferredoxin then transfers the electrons
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to the ferredoxin NADP reductase, also known as FNR.
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After two electrons are transferred to FNR,
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NADPH is made by adding the two electrons and a hydrogen
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ion to NADP.
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The gradient created by the electron transport chain
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is utilized by ATP synthase to create ATP from ADP and PI.
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This is similar to the way ATP is synthesized
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in the mitochondria.
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ATP, NADPH, and molecular oxygen are the final vital products
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of photosynthesis.
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- Idioma/s:
- Autor/es:
- Virtual Cell
- Subido por:
- Benito H.
- Licencia:
- Reconocimiento - No comercial - Compartir igual
- Visualizaciones:
- 1306
- Fecha:
- 10 de septiembre de 2010 - 12:30
- Visibilidad:
- Público
- Enlace Relacionado:
- Benito Hernández giménez
- Centro:
- IES MORATALAZ
- Descripción ampliada:
- La fotosíntesis es la conversión de energía luminosa en energía química estable, siendo el adenosín trifosfato (ATP) la primera molécula en la que queda almacenada esa energía química.Los orgánulos citoplasmáticos encargados de la realización de la fotosíntesis son los cloroplastos, unas estructuras polimorfas y de color verde (esta coloración es debida a la presencia del pigmento clorofila) propias de las células vegetales. En el interior de estos orgánulos se halla una cámara que contiene un medio interno llamado estroma, que alberga diversos componentes, entre los que cabe destacar enzimas encargadas de la transformación del dióxido de carbono en materia orgánica y unos sáculos aplastados denominados tilacoides o lamelas, cuya membrana contiene pigmentos fotosintéticos.
- Duración:
- 05′ 04″
- Relación de aspecto:
- 1.31:1
- Resolución:
- 1024x780 píxeles
- Tamaño:
- 25.54 MBytes
