Name: photosystem ii and water splitting
Uploaded: 2019-03-11T09:21:12.000Z
Duration: 1 min 22 s
Channel: JoVE

K12 Standards

Louisiana Student Standards for Science

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Environmental Science

Earth’s Systems

HS-ESS2-6

Photosystem II

- No Fotossistema II, complexo multiproteico, fótons são absorvidos e sua energia é passada através da porção de luz por muitas moléculas de pigmentos ligados tais como, clorofila A e B, e os carotenóides. 
Esta absorção ativa gera energia que é transferida a um par de moléculas de clorofila conhecido como P680 no centro de reação. 
Aqui, as duas clorofilas são especializadas para sofrer oxidação onde elas desistem de um elétron excitado para a molécula primária de receptores de elétrons em um processo chamado Fotoativação. 
O elétron ausente é então substituído dividindo a água em dois íons de hidrogênio e um átomo de oxigênio liberando dois elétrons que são fornecidos um por um ao centro de reação. 
Agora, os elétrons estão prontos para viajar pela cadeia de transporte de elétrons para o Fotossistema I. 
O oxigênio pode combinar com outro oxigênio da água para formar um gás que escapa para a atmosfera e o acúmulo de íons de hidrogênio dentro do tilacoide cria um gradiente de concentração em que aqueles na área de alta concentração fluem através de um canal proteico semi-permeável especializado chamado, ATP sintase em uma área de baixa concentração no estroma. 
Este processo é conhecido como quimiosmose e cria energia permitindo que a ATP sintase ligue um terceiro grupo fosfato ao ADP para formar o produto energético ATP.

<ol>
	<li>Sasi, Shina, Jelli Venkatesh, Rawya Fatohllah Daneshi e Mayank Anand Gururani. "Proteínas extrínsecas do fotossistema II e seu papel putativo na tolerância ao estresse abiótico em plantas superiores." Plantas 7, nº 4 (dezembro de 2018): 100.</li>
	<li>Yamamoto, Yasusi. "Controle de qualidade do fotossistema II: os mecanismos de prevenção e tolerância a tensões luminosas e térmicas estão intimamente ligados à fluidez da membrana dos tilacóides." Fronteiras na Ciência das Plantas 7 (2016).</li>
</ol>

fotossistema ii

<h4>Visão Geral</h4>
 
 O Fotossistema II é um complexo multi-proteico incorporado dentro da membrana de tilacóides onde recolhe energia da luz. Moléculas de clorofila transferem energia para um par específico de moléculas de clorofila a no centro reativo do Fotossistema II. Aqui, as moléculas de clorofila a perdem um eletrão (oxidação), transferindo-o para um aceitador de eletrões primário. Os eletrões doados passam pela cadeia de transporte de eletrões para o Fotossistema I. A divisão de uma molécula de água liberta um átomo de oxigénio, dois protões (H+) e dois eletrões. Os eletrões substituem os eletrões dados das duas moléculas de clorofila a no centro reativo. O átomo de oxigénio reage imediatamente com outro átomo de oxigénio, produzindo O2 que é libertado na atmosfera. Os protões acumulam-se e criam um gradiente de concentração através da membrana dos tilacóides que guia a síntese de ATP em um processo chamado quimiosmose.
 
 <h4>Captura de Luz no Fotossistema II</h4>
 
 O complexo multi-proteico do Fotossistema II captura fotões e transfere energia através dos seus pigmentos associados clorofila a e b, e carotenóides. Os carotenóides têm uma função protetora, pois ajudam a dissipar a vasta quantidade de energia capturada que poderia danificar o tecido vegetal.
 
 A energia viaja de molécula de clorofila para molécula de clorofila até atingir um par de moléculas de clorofila especializadas em uma região chamada centro reativo. O centro reativo também é conhecido como P680, pois absorve luz em um comprimento de onda de 680 nm. A energia é forte o suficiente para quebrar um eletrão de uma molécula de clorofila (oxidação). O eletrão livre é transferido para uma molécula aceitadora de eletrões primária, em um processo chamado fotoato. O eletrão da clorofila a no centro reativo é substituído por um dos dois eletrões que são libertados na divisão de uma molécula de água.
 
 <h4>Gradiente de Protões e Produção de ATP</h4>
 
 A divisão da água no Fotossistema II também dá origem a um átomo de oxigénio que se combina com um segundo átomo de oxigénio. O O2 resultante escapa para a atmosfera. A reação também gera dois protões ( H+) que se acumulam e criam um gradiente de concentração para alimentar um canal proteico especializado e semi-permeável chamado ATP sintase. O processo em que os protões se movem de uma alta concentração no tilacóide, através do canal para uma zona de concentração mais baixa no estroma é chamado de quimiosmose. A quimiosmose cria energia que permite que a ATP sintase ligue um terceiro grupo fosfato ao ADP para formar a molécula de energia ATP.

Fotossistema II

O complexo fotossistema multiproteico II (PS II) colhe fótons e transfere sua energia através de seus pigmentos ligados para seu centro de reação, e ...

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photosystem ii and water splitting

Photosystem II is a multi-protein complex that captures light energy and begins the flow of electrons in photosynthesis. It uses bound pigments to harvest photons and send that energy to its reaction center. From there, the energy continues through the electron transport chain and on to photosystem I.

The pigments in photosystem II include chlorophyll a, chlorophyll b, and carotenoids. They are arranged in two parts of the photosystem: the antenna complex and the reaction center. The antenna complex absorbs light and funnels that energy to the special chlorophyll pair in the reaction center.

Carotenoids also have a protective role. They help dissipate excess absorbed energy and reduce damage to plant tissue. In the reaction center, also called P680, a photon excites an electron in chlorophyll. The high-energy electron is released and passed to the primary electron acceptor.

P680 then replaces the lost electron by taking low-energy electrons from water splitting. Splitting one H2O molecule releases two electrons, two hydrogen atoms, and one oxygen atom. Two oxygen atoms from two H2O molecules join to form oxygen gas, which is released into the environment. The hydrogen ions also help build the proton gradient across the thylakoid membrane. That gradient is essential for ATP synthesis in the chloroplast.

Photosystem II and Water Splitting

what is photosynthesis?

Photosynthesis in Chloroplasts and Leaves

Photosynthesis happens in plants and in some bacteria. It is the process that captures carbon dioxide and solar energy to make glucose. Glucose stores chemical energy as carbohydrates. The overall biochemical equation is 6 CO2 + 6 H2O + light energy → C6H12O6 + 6 O2. Photosynthesis also releases oxygen into the atmosphere and helps maintain Earth’s atmospheric oxygen content. Photosynthetic reactions take place in chloroplasts, which are specialized membrane-enclosed parts of the plant cell.

light as energy

How Plant Pigments Capture Light

Photosynthesis uses light energy from the sun, which is a form of electromagnetic radiation. The full range of possible wavelengths is called the electromagnetic spectrum. Light is made of photons, which are small packets of energy. Photons act like waves and are described by frequency, wavelength, and amplitude. Waves with higher frequencies carry more energy and have shorter wavelengths. Waves with lower frequencies carry less energy and have longer wavelengths. For most organisms,...

anatomy of chloroplasts

Chloroplasts and Photosynthesis in Plant Cells

Chloroplasts are the organelles where photosynthesis takes place in green algae and plants. They are also found in green stems and unripe fruit. In plants, mesophyll cells in the leaf contain the highest density of chloroplasts. Each chloroplast has a double membrane. The outer membrane faces the plant cell cytoplasm on one side and the chloroplast intermembrane space on the other. The inner membrane separates that narrow space from the stroma, which is the watery interior of the chloroplast.

photosystem ii

Photosystem II is a multi-protein complex that captures light energy and begins the flow of electrons in photosynthesis. It uses bound pigments to harvest photons and send that energy to its reaction center. From there, the energy continues through the electron transport chain and on to photosystem I. The pigments in photosystem II include chlorophyll a, chlorophyll b, and carotenoids. They are arranged in two parts of the photosystem: the antenna complex and the reaction center. The antenna...

photosystem i

Photosystem I and NADPH Formation

Photosystem I helps convert light energy into NADPH during photosynthesis. It works with photosystem II in the thylakoid membrane of the chloroplast, but it uses a different electron supplier and a different electron acceptor. Electrons excited in photosystem II move to photosystem I through an electron transport chain. That chain includes plastoquinone, the dual-protein cytochrome complex, and plastocyanin. As the electrons travel between the two photosystems, they lose energy and must be...

the calvin cycle

Carbon Fixation in Photosynthesis

Photosynthesis uses light energy to turn carbon dioxide into carbohydrates. It also releases oxygen as a by-product. These products help support most food webs and make aerobic life possible. Photosynthesis has two main stages, and they happen in different parts of the chloroplast. The light-dependent reactions take place in the thylakoid membranes. Chlorophyll absorbs light energy there and helps split water molecules. This releases O2 and makes ATP and NADPH. The light-independent reactions...

c4 pathway and cam

Plant Carbon Fixation in Hot Climates

Plant carbon fixation in hot climates can follow the C4 pathway or the CAM pathway. These alternative pathways help some plants reduce energy loss from photorespiration. Photorespiration happens when oxygen levels are high and rubisco, the enzyme in the Calvin cycle, binds O2 instead of CO2. When that happens, photosynthesis slows and energy is used up. The C4 pathway is used by plants such as corn and sugarcane. In mesophyll cells, CO2 first joins with PEP, or phosphoenolpyruvate, through the...

key terms and concepts

Learn how photosystem II captures light, excites P680, splits water, releases oxygen, and helps build the proton gradient needed for ATP synthesis.

Photosystem II and Water Splitting | JoVE K12

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Photosystem II and Water Splitting

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