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

在自养植物中， 当大气中的二氧化碳 最终扩散到叶绿体的基质中时，卡尔文循环便开始了。
 在此，将来自二氧化碳的一个碳原子 添加或固定到 五碳受体糖分子上， 二磷酸核酮糖，或RuBP， 在由酶催化的化学反应中 核酮糖1,5-二磷酸-羧化酶-加氧酶， 或简称RuBisCo。
 得到的六碳分子非常不稳定 并分成两个三碳分子 3-磷酸​甘油酸，3-PGA。
 ATP提供能量， 和NADPH每个都加一个氢 三条PGA链转化为另一种 三碳中间体 称为甘油醛-3-磷酸。
 然后一个G3P退出循环 并等待另一个人建立葡萄糖 含有六个碳原子。
 与此同时，剩余的G3P必须等待 四次循环，积累着碳， 和ATP提供更多能量 重新生成RuBP受体。
 总的来说，卡尔文周期有六个回合 从大气中固定六氧化碳 使用能量和减少能量 分别为18个ATP和12个NADPH 产生一分子葡萄糖 并重建RuBP以继续循环。

Michelet， Laure， Mirko Zaffagnini， Samuel Morisse， Francesca Sparla， María Esther Pérez-Pérez， Francesco Francia， Antoine Danon， et al. "卡尔文-本森循环的氧化还原调控:旧的东西，新的东西。植物科学前沿 4 （2013）。[<a href="https://doi.org/10.3389/fpls.2013.00470" target="__blank">来源</a>]

Sharkey、Thomas D. 和 Sean E. Weise。"卡尔文-本森循环周围的葡萄糖 6-磷酸分流。"实验植物学杂志 67，第 14 期（2016 年 7 月 1 日）:4067-77。[<a href="https://doi.org/10.1093/jxb/erv484" target="__blank">来源</a>]

卡尔文循环

氧光合作用每年将约2000亿吨二氧化碳（CO2）转化为有机化合物，并产生约1400亿吨大气氧（O2）。光合作用是人类所有食物和氧气需求的基础。

光合过程可分为两组发生在植物叶绿体不同区域的反应：光依赖反应和光独立或暗反应。光依赖反应发生在叶绿体的类囊体膜上。它将光能转换成化学能，储存为ATP和NADPH。然后在叶绿体的基质区域中利用这种能量，通过卡尔文循环（Calvin-Benson Cycle）的光独立反应将大气二氧化碳还原成复杂碳水化合物。
 
<h4>卡尔文循环（Calvin-Benson Cycle）</h4>
 
卡尔文循环代表光独立的光合反应集合。它利用在光依赖反应中产生的三磷酸腺苷(ATP)和烟酰胺腺嘌呤二核苷酸磷酸酯 (NADPH) 将大气中的CO2转化为复杂的碳水化合物。卡尔文循环还可再生二磷酸腺苷 (ADP)和NADP+，用于光依赖反应。
 
在卡尔文循环开始时，大气CO2通过气孔进入叶片。在叶绿体基质区，核酮糖-1,5-二磷酸羧化酶/加氧酶(RuBisCO)将一个碳原子从CO2添加到5-碳 (5C)受体糖分子，核酮糖-1,5-二磷酸 (RuBP。由此产生的6C分子高度不稳定，分裂成两个3-磷酸甘油酸（3-PGA）分子。磷酸甘油酸激酶利用ATP使这些3-PGA分子磷酸化，形成1,3-双磷酸甘油酸。甘油醛3-磷酸脱氢酶利用NADPH还原这些分子，形成甘油醛3-磷酸酯（G3P），一种3C糖。最终产品命名为 C3碳固定，这是 Calvin-Benson循环的别名。
 
为了固定6个CO2分子，卡尔文循环减少了12个 NADPH和18个ATP分子。这些能量来源由光合作用的光依赖反应补充。六个CO2连接到六个5C分子(RuBP)）上，这些5C分子分裂成12个3C分子 (G3P）。其中10个G3P分子再生6个RuBP受体分子，继续循环。G3P的两个分子转化为一个葡萄糖。G3P还可用于合成其它碳水化合物、氨基酸和脂质。

概述

产氧光合作用每年将约2000亿吨二氧化碳（CO2）转化为有机化合物，并产生约……

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细胞结构与功能

Photosynthesis

光合作用

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关键术语与概念

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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3.3.9-12.N

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Carbon Fixation in Photosynthesis

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