Name: carbon fixation in photosynthesis
Uploaded: 2025-08-11T09:30:18.000Z
Duration: 1 min 40 s
Channel: JoVE

K12 Standards

Pennsylvania State Academic Standards

9-12

Earth and Space Science

Earth's Systems

3.3.9-12.L

The Calvin Cycle

Em plantas autotróficas, o ciclo de Calvin começa quando o dióxido de carbono atmosférico eventualmente se difunde no estroma do cloroplasto. Aqui, um átomo de carbono do dióxido de carbono é adicionado ou fixado a uma molécula de açúcar aceitadora de cinco carbonos, a ribulose bifosfato, ou RuBP, em uma reação catalisada pela enzima ribulose 1, 5 o bisfosfato carboxilase oxigenase, ou RuBisCo para abreviar. A molécula resultante de seis carbonos é altamente instável e se divide em duas moléculas de três carbonos de 3-fosfoglicerato, 3-PG.Com o ATP fornecendo a energia, e o NADPH fixando um hidrogénio para cada um, as cadeias de 3-PG são convertidas em outra de três carbonos intermediária chamada gliceraldeído-3-fosfato. Um G3P então sai do ciclo e espera por outro construir uma hexose fosforilada com seis átomos de carbono. Enquanto isso, o G3P restante deve esperar por mais quatro ciclos à medida que os carbonos se acumulam e o ATP fornece mais energia para regenerar os aceitadores do RuBP.No geral, seis voltas do Ciclo de Calvin fixam seis dióxidos de carbono da atmosfera usando a energia e reduzindo o poder de 18 ATPs e 12 NADPHs, respetivamente. Isso gera uma hexose, que pode ser posteriormente metabolizada, e reconstrói o RuBP para continue o ciclo.

Michelet, Laure, Mirko Zaffagnini, Samuel Morisse, Francesca Sparla, María Esther Pérez-Pérez, Francesco Francia, Antoine Danon, et al. "Regulação redox do ciclo de Calvin-Benson: algo velho, algo novo." Fronteiras em Ciência das Plantas 4 (2013). [<a href="https://doi.org/10.3389/fpls.2013.00470" target="__blank">Fonte</a>]

Sharkey, Thomas D. e Sean E. Weise. "O Shunt de Glicose 6-Fosfato em torno do Ciclo Calvin-Benson." Journal of Experimental Botany 67, nº 14 (1º de julho de 2016): 4067–77. [<a href="https://doi.org/10.1093/jxb/erv484" target="__blank">Fonte</a>]

o ciclo de calvin

<h4>Visão Geral</h4>
 
 A fotossíntese oxigénica converte aproximadamente 200 mil milhões de toneladas de dióxido de carbono (CO2) anualmente em compostos orgânicos e produz aproximadamente 140 mil milhões de toneladas de oxigénio atmosférico (O2). A fotossíntese é a base de todas as necessidades humanas de alimento e oxigénio.
 
 O processo fotossintético pode ser dividido em dois conjuntos de reações que ocorrem em diferentes zonas dos cloroplastos das plantas: a reação dependente da luz e as reações independentes da luz ou “escuras”. A reação dependente da luz ocorre na membrana dos tilacóides do cloroplasto. Converte energia da luz em energia química, armazenada como ATP e NADPH. Essa energia é então utilizada na região do estroma do cloroplasto, para reduzir o dióxido de carbono atmosférico em carboidratos complexos através das reações independentes da luz do ciclo de Calvin-Benson.
 
 <h4>O Ciclo de Calvin-Benson</h4>
 
 O ciclo de Calvin-Benson representa o conjunto das reações fotossintéticas independentes da luz. Ele usa o trifosfato de adenosina (ATP) e o fosfato de dinucleótido de adenina e nicotinamida (NADPH) produzido durante as reações dependentes da luz para converter CO2 atmosférico em carboidratos complexos. O ciclo de Calvin-Benson também regenera difosfato de adenosina (ADP) e NADP+ para a reação dependente da luz.
 
 No início do ciclo de Calvin-Benson, o CO2 atmosférico entra na folha através de aberturas chamadas estomas. Na região do estroma do cloroplasto, a enzima ribulose-1,5-bifosfato carboxilase oxigenase (RuBisCO) adiciona um átomo de carbono do CO2 a uma molécula de açúcar aceitadora de 5 carbonos (5C), ribulose-1,5- bifosfato (RuBP). A molécula de 6C resultante é altamente instável e divide-se em duas moléculas de ácido 3-fosfoglicérico (3-PGA). A enzima 3-fosfoglicerato quinase usa ATP para fosforilar essas moléculas de 3-PGA para formar 1,3-bifosfoglicerato. A gliceraldeído 3-fosfato desidrogenase usa NADPH para reduzir essas moléculas para formar gliceraldeído 3-fosfato (G3P), um açúcar de 3C. Este produto final dá origem ao nome fixação do carbono C3—um pseudónimo para o ciclo de Calvin-Benson.
 
 Para fixar seis moléculas de CO2, o ciclo de Calvin-Benson reduz 12 moléculas de NADPH e 18 de ATP. Essas fontes de energia são reabastecidas pelas reações dependentes da luz da fotossíntese. Os seis CO2 são ligados a seis moléculas de 5C (RuBP) que se dividem em 12 moléculas de 3C (G3P). Dez dessas moléculas de G3P regeneram seis moléculas do aceitador RuBP, para continuar o ciclo. Duas moléculas de G3P são convertidas em uma glicose. O G3P também pode ser usado para sintetizar outros carboidratos, aminoácidos e lípidos.

O Ciclo de Calvin

Visão geral

A fotossíntese oxigenada converte aproximadamente 200 bilhões de toneladas de dióxido de carbono (CO2) anualmente em compostos orgânicos e produz aproximadamente ...

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Biology

Biologia

Cellular Processes

Processos Celulares

Photosynthesis

Fotossíntese

KEY TERMS AND CONCEPTS

TERMOS-CHAVE E CONCEITOS

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 happen in the stroma, where the Calvin-Benson cycle operates. This cycle uses ATP and NADPH to reduce atmospheric CO2 into carbohydrates. After they are used, ADP and NADP+ return to the thylakoids so the light reactions can recycle them.

The Calvin-Benson cycle has three phases: carbon fixation, reduction, and regeneration of the CO2 acceptor, RuBP. CO2 enters the leaf through stomata. In the stroma, the enzyme RuBisCO attaches each CO2 molecule to ribulose-1,5-bisphosphate, or RuBP. This forms an unstable six-carbon intermediate that quickly splits into two molecules of 3-phosphoglycerate, or 3-PGA.

During reduction, each 3-PGA molecule is phosphorylated by ATP to form 1,3-bisphosphoglycerate. NADPH then reduces it to glyceraldehyde-3-phosphate, or G3P, a three-carbon sugar. For every six CO2 molecules fixed, two G3P molecules leave the cycle. These molecules help form glucose and other organic compounds.

In the final regeneration phase, the remaining G3P molecules are rearranged to rebuild RuBP. This step uses additional ATP. Regenerating RuBP lets the cycle continue fixing CO2.

Carbon Fixation in Photosynthesis

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 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...

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

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

Explore how the Calvin-Benson cycle fixes carbon dioxide into sugars, using ATP and NADPH in the chloroplast stroma during photosynthesis.

Carbon Fixation in Photosynthesis | JoVE K12

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3.3.9-12.N

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Carbon Fixation in Photosynthesis

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