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

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3.3.9-12.L

The Calvin Cycle

в автотрофных растениях, цикл Кальвина начинается, когда атмосферный углекислый газ в конце концов, проникает в строму хлоропласта. Здесь один атом углерода из углекислого газа, или из фиксированного на молекуле пятиуглеродного сахара-акцептора, рибулозного бифосфата, или Rubp. В реакции, катализированной по ферменту рибулоза 1, 5 бифозефат-карбоксилаза-оксигеназа, или коротко, RubisCo.Получившаяся шестиугольная молекула очень нестабильна и разделяется на две трехуглеродные молекулы трех фосфоглицериновых кислот, 3-PGA. С ATPФ, обеспечивающей энергию и NADPН, прикрепляющим по одному водороду к каждому, цепи 3-PGA преобразуются в ещё один трехкарбонный промежуточный продукт, называемый глицердегид-3-фосфат. Затем один G3P выходит из цикла и ждёт ещё одного для создания глюкозы с шестью атомами углерода.Тем временем, остальным G3P необходимо подождать ещё четыре цикла по мере накопления углерода А ATФ обеспечивает больше энергии для регенерации акцепторов Rubp. В целом, шесть прогонов цикла Кальвина устраняют шесть диоксидов углерода из атмосферы. Использование энергии и снижение мощности из 18 АТФ и 12 NADPH, соответственно, генерирует одну молекулу глюкозы и перестраивает Rubp, чтобы продолжить цикл.

Мишле, Лоре, Мирко Заффаньини, Самуэль Морисс, Франческа Спарла, Мария Эстер Перес-Перес, Франческо Франсиа, Антуан Данон и др. "Окислительно-восстановительная регуляция цикла Кальвина-Бенсона: что-то старое, что-то новое." Frontiers in Plant Science 4 (2013). [<a href="https://doi.org/10.3389/fpls.2013.00470" target="__blank">Источник</a>]

Шарки, Томас Д. и Шон Э. Вайз. «Шунт глюкозы-6-фосфата вокруг цикла Кальвина-Бенсона». Журнал экспериментальной ботаники 67, No 14 (1 июля 2016 г.): 4067–77. [<a href="https://doi.org/10.1093/jxb/erv484" target="__blank">Источник</a>]

Восстановительный пентозофосфатный цикл, или цикл Кальвина

<h4>Обзор</h4>

Кислородный фотосинтез преобразует около 200 миллиардов тонн углекислого газа (CO2) в год в органические соединения и производит около 140 миллиардов тонн атмосферного кислорода (O2). Фотосинтез является основой всех потребностей человека в пище и кислороде.

Фотосинтетический процесс можно разделить на два набора реакций, которые происходят в разных регионах хлоропластов растений: светозависимые реакции и светозависимые или "темные" реакции. Светозависимые реакции происходят в тилакоидной мембране хлоропласта. Он преобразует световую энергию в химическую энергию, хранящуюся в качестве АТФ и NADPH. Эта энергия затем используется в области стромы хлоропласта, чтобы уменьшить содержание углекислого газа в атмосфере в сложные углеводы через свето-независимые реакции цикла Кальвина-Бенсона.

<h4>Цикл Кэльвина-Бенсона</h4>

Цикл Кэльвина-Бенсона представляет собой свето-независимый набор фотосинтетических реакций. Он использует аденозинтрифосфат (АТФ) и никотинамид-аденин динуклеотид фосфат (NADPH), генерируемый во время светозависимых реакций для преобразования атмосферного CO2 в сложные углеводы. Цикл Кэльвина-Бенсона также регенерирует аденозин-дипфосфат (ADP) и NADPдля светозависимых реакций.

В начале цикла Кэльвина-Бенсона атмосферный CO2 попадает в лист через отверстия, называемые стоматой. В области стромы хлоропласта фермент рибулоза-1,5-бисфосфат карбоксилазы/оксигеназы (RuBisCO) добавляет один атом углерода от CO2 до 5-углеродной (5C) молекулы сахара-акцептора, рибулозы-1,5-бисфосфата (RuBP). Полученная молекула 6C очень нестабильна и распадается на две молекулы 3-фосфоглицерной кислоты (3-PGA). Фермент 3-фосфоглицерат киназы использует АТФ для фосфорилата этих 3-PGA молекул для формирования 1,3-бисфосфоглицерат. Глицеральдегид 3-фосфат дегидрогеназа использует NADPH, чтобы уменьшить эти молекулы для формирования глицеральдегид 3-фосфат (G3P), 3C сахара. Этот конечный продукт дает название C3 фиксации углерода-псевдоним для цикла Кэльвина-Бенсона .

Чтобы исправить шесть молекул CO2, цикл Кэльвина-Бенсона уменьшает 12 NADPH и 18 молекул АТФ. Эти источники энергии пополняются светозависимыми реакциями фотосинтеза. Шесть CO2 прилагаются к шести молекулам 5C (RuBP), которые распадаются на 12 молекул 3C (G3P). Десять из этих молекул G3P регенерируют шесть молекул приёмщика RuBP, чтобы продолжить цикл. Две молекулы G3P преобразуются в одну глюкозу. G3P также может быть использован для синтеза других углеводов, аминокислот и липидов.

Обзор

Кислородный фотосинтез ежегодно преобразует около 200 миллиардов тонн углекислого газа (CO2) в органические соединения и производит около ...

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KEY TERMS AND CONCEPTS

ОСНОВНЫЕ ТЕРМИНЫ И ПОНЯТИЯ

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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