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

- [Narrador] En las plantas
autotrópicas, el ciclo de Calvin

comienza cuando el dióxido
de carbono atmosféricos

eventualmente se dispersa en
el estroma del cloroplasto.

Aquí, un átomo de carbón
de dióxido de carbono

se agrega o fija

a una molécula de azúcar
receptora de cinco carbonos,

la ribulosa bifosfato, o RuBP,

en una reacción catalizada por la encima

ribulosa-1,5-bifosfato
carboxilasa/oxigenasa,

o RuBisCo.

La molécula de seis carbonos
resultante es muy inestable

y se divide en dos
moléculas de tres carbonos

de ácido 3-fosfoglicérico, 3-PGA.

Con el ATP aportando la energía,

y la NADPH fijando un
hidrógeno a cada una,

las cadenas de 3-PGA se convierten

en otro intermediario de tres carbonos

llamado gliceraldehído-3-fosfato.

Un G3P entonces sale del ciclo

y espera a otro para formar glucosa

con seis átomos de carbono.

Mientras, el G3P restante debe esperar

cuatro ciclos más mientras
se acumula el carbono

y el ATP aporta más energía

para regenerar los receptores de RuBP.

En total, seis vueltas del ciclo de Calvin

fijan seis dióxidos de
carbono de la atmósfera

usando la energía y reduciendo el poder

de 18 ATPs y 12 NADPHs, respectivamente,

para generar una molécula de glucosa

y reconstruir RuBP para
continuar el ciclo.

Michelet, Laure, Mirko Zaffagnini, Samuel Morisse, Francesca Sparla, María Esther Pérez-Pérez, Francesco Francia, Antoine Danon, et al. "Regulación redox del ciclo de Calvin-Benson: algo viejo, algo nuevo". Frontiers in Plant Science 4 (2013). [<a href="https://doi.org/10.3389/fpls.2013.00470" target="__blank">Fuente</a>]

Sharkey, Thomas D. y Sean E. Weise. "La derivación de glucosa 6-fosfato alrededor del ciclo de Calvin-Benson". Revista de Botánica Experimental 67, no. 14 (1 de julio de 2016): 4067–77. [<a href="https://doi.org/10.1093/jxb/erv484" target="__blank">Fuente</a>]

el ciclo de calvin

<h4>Descripción general</h4> La fotosíntesis oxigénica convierte aproximadamente 200 mil millones de toneladas de dióxido de carbono (CO2) anualmente en compuestos orgánicos y produce aproximadamente 140 mil millones de toneladas de oxígeno atmosférico (O2). La fotosíntesis es la base de todas las necesidades humanas de alimentos y oxígeno. El proceso fotosintético se puede dividir en dos conjuntos de reacciones que tienen lugar en diferentes regiones de los cloroplastos de las plantas: la reacción dependiente de la luz y las reacciones independientes de la luz u “oscuras”. La reacción dependiente de la luz tiene lugar en la membrana tilacoide del cloroplasto. Convierte la energía luminosa en energía química, almacenada como ATP y NADPH. Luego, esta energía se utiliza en la región del estroma del cloroplasto para reducir el dióxido de carbono atmosférico en carbohidratos complejos a través de reacciones independientes de la luz del ciclo de Calvin-Benson. <h4>El ciclo de Calvin-Benson</h4> El ciclo de Calvin-Benson representa el conjunto de reacciones fotosintéticas independientes de la luz. Utiliza el trifosfato de adenosina (ATP) y el fosfato de dinucleótido de nicotinamida y adenina (NADPH) generados durante las reacciones dependientes de la luz para convertir el CO2 atmosférico en carbohidratos complejos. El ciclo de Calvin-Benson también regenera difosfato de adenosina (ADP) y NADP+ para la reacción dependiente de la luz. Al comienzo del ciclo de Calvin-Benson, el CO2 atmosférico ingresa a la hoja a través de aberturas llamadas estomas. En la región del estroma del cloroplasto, la enzima ribulosa-1,5-bisfosfato carboxilasa/oxigenasa (RuBisCO) añade un átomo de carbono del CO2 a una molécula de azúcar aceptora de 5 carbonos (5C), la ribulosa-1,5-bisfosfato (RuBP). La molécula de 6C resultante es muy inestable y se divide en dos moléculas de ácido 3-fosfoglicérico (3-PGA). La enzima 3-fosfoglicerato quinasa utiliza ATP para fosforilar estas moléculas de 3-PGA para formar 1,3-bisfosfoglicerato. La gliceraldehído 3-fosfato deshidrogenasa utiliza NADPH para reducir estas moléculas y formar gliceraldehído 3-fosfato (G3P), un azúcar 3C. Este producto final da origen al nombre de fijación de carbono C3,un alias del ciclo de Calvin-Benson.

Para fijar seis moléculas de CO2, el ciclo de Calvin-Benson reduce 12 moléculas de NADPH y 18 de ATP. Estas fuentes de energía se reponen mediante reacciones de la fotosíntesis dependientes de la luz. Los seis CO2 están unidos a seis moléculas de 5C (RuBP) que se rompen en 12 moléculas de 3C (G3P). Diez de estas moléculas de G3P regeneran seis moléculas del aceptor de RuBP para continuar el ciclo. Dos moléculas de G3P se convierten en una glucosa. El G3P también se puede utilizar para sintetizar otros carbohidratos, aminoácidos y lípidos.

El ciclo de Calvin

Visión general

La fotosíntesis oxigénica convierte aproximadamente 200 mil millones de toneladas de dióxido de carbono (CO2) anualmente en compuestos orgánicos y produce aproximadamente ...

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Procesos celulares

Photosynthesis

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KEY TERMS AND CONCEPTS

TÉRMINOS Y CONCEPTOS CLAVE

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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