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

K12 Standards

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Earth and Space Science

Earth's Systems

3.3.9-12.L

The Calvin Cycle

In autotrophen Pflanzen startet der Calvin-Zyklus, wenn atmosphärisches CO2 sich im Stroma des Chloroplasten ausbreitet.
 Hier wird ein Kohlenstoff-Atom des CO2 einem fünf Kohlenstoff-Akzeptor Zucker-Molekül beigefügt, Ribulose Biphosphat, oder RuBP, in einer Reaktion, die katalysiert wird vom Enzym Ribulose 1-5-Biphospat-Carboxylase-Oxygenase, oder kurz auch RuBisCo.
 Das entstehende 6-Kohlenstoff-Molekül ist sehr instabil in spaltet sich in zwei 3-Kohlenstoff-Moleküle von 3-Phosphoglycerischen Säuren, 3-PGA, wobei ATP die Energie beiträgt und NADPH ein Hydrogen an jedes fixiert; die 3-PGA-Ketten werden zu noch einmal 3-Kohlenstoff- Zwischengliedern konvertiert, was Glyceraldehyde-3-Phosphat heißt.
 Ein G3P verlässt den Zyklus und wartet auf den nächsten, um Glukose mit sechs Kohlenstoff-Atomen zu bauen.
 Währenddessen muss das verbleibende G3P auf Zyklen warten, während sich Kohlenstoff ansammelt und ATP mehr Energie bietet, um die RuBP-Akzeptoren zu regenerieren.
 Insgesamt festigen sechs Durchläufe des Calvin-Zyklus sechs CO2 von der Atmosphäre, und sie nutzen die Energie und Reduzierungskraft von 18 ATP und 12 NADPH jeweils, um ein Molekül Glukose zu generieren und RuBP zu bauen, um den Kreislauf weiterzuführen.

Michelet, Laure, Mirko Zaffagnini, Samuel Morisse, Francesca Sparla, María Esther Pérez-Pérez, Francesco Francia, Antoine Danon, et al. "Redoxregulation des Calvin-Benson-Zyklus: Etwas Altes, etwas Neues." Frontiers in Plant Science 4 (2013). [<a href="https://doi.org/10.3389/fpls.2013.00470" target="__blank">Quelle</a>]

Sharkey, Thomas D. und Sean E. Weise. "Der Glukose-6-Phosphat-Shunt um den Calvin-Benson-Zyklus." Journal of Experimental Botany 67, Nr. 14 (1. Juli 2016): 4067–77. [<a href="https://doi.org/10.1093/jxb/erv484" target="__blank">Quelle</a>]

calvin-zyklus

<h4>Überblick</h4>
 
 Die Fotosynthese wandelt jährlich ca. 200 Milliarden Tonnen Kohlendioxid (CO2) in organische Verbindungen um und produziert ca. 140 Milliarden Tonnen Luftsauerstoff (O2). Die Fotosynthese bildet somit die Grundlage für die menschliche Nahrungs-und Sauerstoffaufnahme.
 
 Der fotosynthetische Prozess kann in zwei verschiedene Arten von Reaktionen unterteilt werden, welche in verschiedenen Regionen der pflanzlichen Chloroplasten ablaufen. Es gibt die lichtabhängige und die lichtunabhängige Reaktion. Die lichtabhängige Reaktion findet in der Thylakoidmembran eins Chloroplasts statt. Bei dieser wird Lichtenergie in chemische Energie umgewandelt und in Form von ATP und NADPH gespeichert. Diese Energie wird dann im Stroma des Chloroplasten genutzt, um atmosphärischen Kohlendioxid in den lichtunabhängigen Reaktionen des Calvin-Benson-Zyklus in komplexe Kohlenhydrate zu reduzieren.
 
 <h4>Der Calvin-Benson-Zyklus</h4>
 
 Der Calvin-Benson-Zyklus stellt die lichtunabhängigen, fotosynthetischen Reaktionen dar. Er nutzt das Adenosintriphosphat (ATP) und Nikotinamid-Adenin-Dinukleotid-Phosphat (NADPH), die während der lichtabhängigen Reaktionen entstanden sind, um atmosphärisches CO2 in komplexe Kohlenhydrate umzuwandeln. Der Calvin-Benson-Zyklus regeneriert auch Adenosindiphosphat (ADP) und NADP+ für die lichtabhängige Reaktion.
 
 Zu Beginn des Calvin-Benson-Zyklus tritt atmosphärisches CO2 durch sogenannte Spaltöffnungen in das Blatt ein. In dem Stroma des Chloroplasten transferiert das Enzym Ribulose-1,5-Bisphosphat-Carboxylase/Oxygenase (RuBisCO) ein Kohlenstoffatom aus dem aufgenommenen CO2 an ein 5-Kohlenstoff (5C)-Akzeptorzuckermolekül (Ribulose-1,5-Bisphosphat (RuBP). Das resultierende 6C-Molekül ist sehr instabil und spaltet sich in zwei Moleküle 3-Phosphoglycerat (3-PG) auf. Das Enzym 3-Phosphoglyceratkinase verwendet ATP, um diese 3-PG Moleküle zu 1,3-Bisphosphoglycerat zu phosphorylieren. Die Glycerinaldehyd-3-Phosphat-Dehydrogenase verwendet NADPH, um diese Moleküle zu reduzieren und Glycerinaldehyd-3-Phosphat (GAP), einen 3C-Zucker, zu bilden. Aus diesem Endprodukt ergibt sich der Name C3 Kohlenstofffixierung, der ein Alias für den Calvin-Benson-Zyklus ist.
 
 Um sechs CO2 Moleküle zu binden, reduziert der Calvin-Benson-Zyklus 12 NADPH-und 18 ATP-Moleküle. Diese Energiequellen werden durch die lichtabhängigen Reaktionen der Fotosynthese regeneriert. Die sechs CO2 Moleküle sind an sechs 5C-Moleküle (RuBP) gebunden, die in 12 3C-Moleküle (GAP) zerfallen. Zehn dieser GAP-Moleküle regenerieren sechs Moleküle des RuBP-Akzeptors, um den Zyklus fortzusetzen. Zwei GAP-Moleküle werden in eine Glucose umgewandelt. GAP kann auch zur Synthese anderer Kohlenhydrate, Aminosäuren und Lipide verwendet werden.

Calvin-Zyklus

Überblick

Die oxygene Photosynthese wandelt jährlich ca. 200 Milliarden Tonnen Kohlendioxid (CO2) in organische Verbindungen um und produziert ca. ...

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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.

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Carbon Fixation in Photosynthesis

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