章节大纲

  • lesson content

    Other than being green, what do fruits and vegetables have in common?
    ::除了绿色之外,水果和蔬菜有什么共同点?

    They are full of energy in the form of glucose . Fruit and vegetable plants, like all plants, are autotrophs and , producing energy from sunlight. The energy from sunlight is briefly held in NADPH and ATP , which is needed to drive the formation of sugars such as glucose. And this all happens in the Calvin Cycle.
    ::它们充满了葡萄糖形式的能量。像所有植物一样,水果和植物植物是自养的,从阳光中产生能量。阳光的能量短暂地保存在NADPH和ATP,这是驱动葡萄糖等糖的形成所需要的。所有这些都发生在卡尔文循环。

    Photosynthesis Stage II: The Calvin Cycle: Making Food “From Thin Air”
    ::光合作用第二阶段:卡尔文周期:制造食物“从薄空气”

    During the light-dependent stage of , two of the three reactants ( and light) were used to produce oxygen gas, one of the products (and essentially a waste product of this process). All three necessary conditions are required – the with chlorophyll pigments, and catalysts . The first stage transforms light energy into chemical energy, stored to this point in molecules of ATP and NADPH. Look again at the overall equation below. What is left?
    ::在依赖光的阶段,三个反应器中的两个(和光)被用于生产氧气,而氧气是其中的一个产品(基本上是这一过程的废物产品 ) 。 所有三个必要条件都需要 — — 包括叶绿素色素和催化剂。 第一阶段将光能转化为化学能源,储存到这个时候的ATP和NADPH分子中。 再看看下面的总方程式。 剩下的是什么?

    Waiting in the atmosphere is one more reactant, carbon dioxide, and yet to come is the product which is food for all life – glucose. These key players perform in the second stage of the photosynthesis, in which food is “made from thin air.” The second stage of photosynthesis can proceed without light, so its steps are sometimes called “light-independent” or “dark” reactions. Many biologists honor the scientist, Melvin Calvin, who won a 1961 for working out this complex set of chemical reactions , naming it the Calvin Cycle . The Calvin Cycle has two parts. First carbon dioxide is "fixed." Then ATP and NADPH from the provide energy to combine the fixed carbons to make sugar.
    ::在大气中等待是又一个反应力,二氧化碳,然而,未来却是所有生命的食物 — — 葡萄糖 — — 的产品。 这些关键玩家在光合作用第二步表演,即食品“由薄空气制造 ” 。 光合作用第二步可以没有光线地进行,因此其步骤有时被称为“轻度独立”或“黑暗”反应。 许多生物学家向科学家梅尔文·加尔文致敬,他在1961年赢得了一组复杂的化学反应,并命名为卡尔文循环。 卡尔文循环有两个部分。 第一批二氧化碳是“固定的 ” 。 随后,ATP和NADPH从提供能源的能量中将固定的碳组合到制糖。

    Carbon Dioxide is “Fixed”
    ::二氧化碳是“固定的”

    Why does carbon dioxide need to be fixed? Was it ever broken? Life on Earth is carbon-based. Organisms need not only energy but also carbon atoms for building bodies. For nearly all life, the ultimate source of carbon is carbon dioxide (CO 2 ), an inorganic molecule pulled into the producer from the atmosphere. CO 2 , as you saw in Figure , makes up .038% of the Earth's atmosphere.
    ::为何需要固定二氧化碳? 它曾经被破坏过吗? 地球上的生命是以碳为基础的。 生物不仅需要能源,还需要碳原子来建造身体。 对于几乎所有的生命来说,最终的碳来源是二氧化碳(CO2),这是从大气中提取的无机分子。正如图中所示,二氧化碳占地球大气的0. 38%。

    and most other heterotrophs cannot take in CO 2 directly. They must eat other organisms or absorb organic molecules to get carbon. Only autotrophs can build low-energy inorganic CO 2 into high-energy organic molecules like glucose. This process is carbon fixation .
    ::大部分其他的异性营养化物质不能直接吸收二氧化碳。 它们必须吃掉其他有机体或吸收有机分子以获得碳。 只有自发营养可以将低能量无机二氧化碳培养成高能有机分子,比如葡萄糖。 这个过程就是固碳。

    lesson content
    Stomata on the underside of leaves take in CO2 and release water and O2. Guard cells close the stomata when water is scarce. Leaf cross-section (above) and stoma (below).

    Plants have evolved three pathways for carbon fixation. The most common pathway combines one molecule of CO 2 with a 5-carbon sugar called ribulose biphosphate (RuBP). The enzyme which catalyzes this reaction, ribulose-1,5-bisphosphate carboxylase oxygenase (nicknamed RuBisCo ), is the most abundant enzyme on earth! The resulting 6-carbon molecule is unstable, so it immediately splits into two much more stable 3-carbon phosphoglycerate molecules. The 3 carbons in the first stable molecule of this pathway give this largest group of plants the name “C-3.”
    ::植物已经发展了三种碳固化途径。 最常见的途径是将一个二氧化碳分子与一个叫作肋骨双磷酸盐的5碳糖(RuBP)结合起来。 催化这种反应的酶,即肋骨-1、5-双磷酸酯碳气酶(nickname RuBisCo),是地球上最丰富的酶。 由此产生的6碳分子不稳定,因此立即分裂成两个更稳定的3碳磷酸盐分子。 这条途径的第一个稳定分子中的3碳给这个最大的植物组取名为“ C-3 ” 。

    Dry air, hot temperatures, and bright sunlight slow the C-3 pathway for carbon fixation. This is because the stomata , tiny openings under the leaf which normally allow CO 2 to enter and O 2 to leave, must close to prevent loss of water vapor ( Figure ) by transpiration . Closed stomata lead to a shortage of CO 2 . Two alternative pathways for carbon fixation demonstrate biochemical adaptations to differing environments. All three carbon fixation pathways lead to the Calvin Cycle to build sugar.
    ::干燥空气、热温和明光阳光会延缓碳固化的C-3路径。 这是因为通常允许二氧化碳进入和释放O2的叶叶下的细小开口石塔必须接近于防止水蒸气( Figure)因蒸发而流失。 封闭的stomata导致二氧化碳短缺。 固碳的两种替代途径表明对不同环境的生化适应。 所有三种固碳途径都导致卡尔文循环建造糖。

    lesson content
    Even chemical reactions adapt to specific environments. Carbon fixation pathways vary among three groups. Temperate species (maple tree, left) use the C-3 pathway. C-4 species (corn, center) concentrate CO2 in a separate compartment to lessen water loss in hot bright climates. Desert plants (jade plant, right) fix CO2 by CAM photosynthesis only at night, closing stomata in the daytime to conserve water.

    C-4 Plants
    ::C-4 工厂

    Plants such as corn solve the problem by using a separate compartment to fix CO 2 . C-4 plants utilize a specific leaf anatomy. These plants have both bundle-sheath , which are photosynthetic cells arranged into tightly packed coverings or sheaths around the veins of a leaf, and loosely arranged mesophyll cells, which lie between the bundle sheath cells and the leaf surface. The bundle-sheath cells form a protective covering on leaf veins. The Calvin Cycle is confined to the chloroplasts of these bundle sheath cells in C-4 plants. Instead of direct fixation to RuBisCO in the Calvin Cycle, CO 2 is incorporated into a 4-carbon organic acid, which has the ability to regenerate CO 2 in the chloroplasts of the bundle sheath cells. Bundle sheath cells can then utilize this CO 2 to generate by the conventional C-3 pathway.
    ::玉米等植物用单独的隔板来修补CO2,C-4植物使用特定的叶解剖。这些植物都使用捆绑式纤维,即光合细胞,在叶子的血管周围被紧紧包裹或包扎,以及松绑式的中间细胞,这些细胞位于捆绑式纤维细胞和叶子表面之间。捆绑式纤维细胞形成叶静脉的保护罩。卡尔文循环局限于C-4植物中这些捆绑式纤维细胞的叶片。CO2不是直接固定在卡尔文循环中的RuBisCO,而是被纳入一种4碳有机酸,它有能力在捆绑式细胞的叶片中再生CO2。Bundlesheth细胞随后可以利用这种CO2来通过常规的C-3途径生成。

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    In this diagram of the cross section of a leaf, bundle sheath cells can be seen in pink around a leaf vein, and mesophyll cells can be seen in green surrounding the bundle sheath cells and the outer layers of the leaf. Also noticeable is a cut-away of two guard cells (purple) surrounding a stomata.

    In these C-4 plants, fixation of CO 2 occurs in mesophyll cells when it combines with a 3-carbon molecule, phosphoenolpyruvate (PEP), resulting in a 4-carbon oxaoloacetate molecule. This reaction is catalyzed by the enzyme PEP carboxylase. Because the first stable organic molecule has four carbons (oxaoloacetate), this adaptation has the name C-4. This 4-carbon molecule is converted into another 4-carbon molecule, malate, which is shuttled unto the bundle-sheath cells, where it is broken down into CO 2 and a 3-carbon pyruvate . When enough CO 2 accumulates, RuBisCo fixes it a second time, this time as part of the Calvin Cycle. The pyruvate is transported back to the mesophyll cell where it is converted into phosphoenolpyruvate, allowing the process to continue. Compartmentalization allows efficient use of low concentrations of carbon dioxide in these specialized plants.
    ::在这些C-4工厂中,当二氧化碳与3碳分子磷化聚苯乙烯(PEP)结合,产生4碳氧代谢分子时,二氧化碳固定化在中间细胞中,产生4碳碳分子。这种反应由酶PEP carboxylase催化。由于第一个稳定的有机分子有四种碳(氧气),因此这种适应性的名称是C-4。这种4碳分子被转化成另一个4碳分子,即石膏,该分子被穿梭到捆状细胞中,该分子被分解成CO2和3碳酸激素。当二氧化碳积累足够多的时候,RuBisco将它第二次固定下来,作为卡尔文循环的一部分。酸盐被运回到中间细胞中,在那里被转化成磷化聚苯丙酸酯,可以继续这一过程。分解允许在这些专门工厂中高效地使用低浓度的二氧化碳。

    CAM Photosynthesis
    ::CAM 相光合成

    Cacti and succulents such as the jade plant avoid water loss by fixing CO 2 only at night. These plants close their stomata during the day (by closing their guard cells) and open them only in the cooler and more humid nighttime hours. Leaf structure differs slightly from that of C-4 plants, but the fixation pathways are similar. The family of plants in which this pathway was discovered gives the pathway its name, Crassulacean Acid Metabolism , or CAM. CAM photosynthesis is an adaptation to arid conditions in some plants. CAM photosynthesis is a two-step process: part occurs during the day and part at night.
    ::Cacti 和 succulents , 如 翡翠厂等, 避免水流失, 只需在夜间固定二氧化碳。 这些植物白天( 关闭其防护室) 关闭其stomata( 关闭其防护室) , 只在更冷和更湿的夜间时间开放这些植物。 叶结构与 C-4 植物略有不同, 但固定路径相似 。 发现这条路径的植物群给路径取名为 Crassulachan 酸代谢, 或 CAM 。 CAM 光合作用是适应某些植物干旱条件的。 CAM 光合作是一种两步过程: 部分发生在白天, 部分发生在晚上 。

    At night, when the stomata are open, CO 2 can enter the leaf cell, but the light reactions of photosynthesis cannot take place, so ATP and NADPH can't be made. The carbon dioxide is fixed in the cytoplasm of mesophyll cells by a PEP reaction similar to that of C-4 pathway, PEP carboxylase combines CO 2 and PEP, making oxalacetate, which is subsequently transformed into malate. But, unlike the C-4 plant, the resulting malate is not immediately passed on to the Calvin Cycle but are stored in vacuoles for later use. The next day, after the sun comes out and the light reactions restart making ATP and NADPH, malate is released from the vacuoles of the mesophyll cells and enters the stroma of the chloroplasts where an enzyme releases the CO 2 , which then enters into the Calvin Cycle.
    ::在晚上,当斯托玛塔打开时,CO2可以进入叶细胞,但是光合作物的光反应无法发生,所以ATP和NADPH无法制造。二氧化碳通过类似于C-4路径的PEP反应固定在间歇性细胞的细胞图层中,PEP carboxylase结合了CO2和PEP,使碳酸盐随后变成石膏。但是,与C-4工厂不同,由此产生的石膏不会立即传递到卡尔文循环,而是储存在真空循环中,供以后使用。第二天,太阳出来后,光反应重新开始产生ATP和NADPH,石膏从微粒细胞的真空中释放出来,进入氯白板的波纹,其中酶释放CO2,然后进入卡尔文循环。

    How Does the Calvin Cycle Store Energy in Sugar?
    ::Calvin循环能源库如何在糖里储存?

    As Melvin Calvin discovered, carbon fixation is the first step of a cycle. Like an electron transport chain , the Calvin Cycle, shown in Figure , transfers energy in small, controlled steps. Each step pushes molecules uphill in terms of energy content. Recall that in the electron transfer chain, excited electrons lose energy to NADPH and ATP. In the Calvin Cycle, NADPH and ATP formed in the light reactions lose their stored chemical energy to build glucose.
    ::Melvin Calvin发现,碳固化是循环的第一步。像电子运输链,如图所示的Calvin Circle,以小的、受控制的步骤转移能量。每一步将分子从能量含量上推向上坡。回顾在电子传输链中,兴奋型电子失去能量给NADPH和ATP。在加尔文循环中,由光反应形成的NADPH和ATP失去了储存的化学能量来制造葡萄糖。

    Use the diagram below to identify the major aspects of the process:
    ::使用下图确定进程的主要方面:

    • the general cycle pattern
      ::一般周期模式
    • the major reactants
      ::主要中继者
    • the products
      ::产品 产品 产品 产品 产品 产品 产品 产品 产品 产品 产品 产品 产品 产品 产品 产品 产品 产品 产品 产品 产品 产品 产品 产品 产品 产品 产品 产品 产品 产品 产品 产品 产品 产品 产品 产品 产品 产品 产品 产品 产品 产品 产品 产品 产品
    lesson content
    Overview of the Calvin Cycle Pathway.

    First, notice where carbon is fixed by the enzyme Rubisco. In C-3, C-4, and CAM plants, CO 2 enters the cycle by joining with 5-carbon ribulose bisphosphate to form a 6-carbon intermediate, which splits (so quickly that it isn't even shown) into two 3-carbon 3-phosphoglycerate molecules. Now look for the points at which ATP and NADPH (made in the light reactions) add chemical energy (“Reduction” in the diagram) to the 3-carbon molecules. The resulting glyceraldehyde-3-phosphate “half-sugars” can enter several different metabolic pathways. One recreates the original 5-carbon precursor, completing the cycle. A second combines two of the 3-carbon molecules to form glucose, the universal fuel for life. The cycle begins and ends with the same 5-carbon RuBP molecule, but the process combines carbon and energy to build carbohydrates – food for life.
    ::首先,通知碳由酶鲁比斯科(Nezyme Rubisco)固定。在C-3、C-4和CAM(CAM)工厂中,二氧化碳与5-碳核素磷酸酯结合,进入循环循环,形成6-碳中间体,该中间体分裂(甚至没有显示)为2-3碳3-硫化硫酸分子。现在,寻找ATP和NADPH(以光反应制成)在3-碳分子中添加化学能量(图中为减少)的点。由此产生的甘油3-3-磷“半糖”可以进入几种不同的代谢途径。其中一种是重建原有的5-碳前体,完成这一循环。第二个是将2个3-碳分子组合成甘油,即生命的通用燃料。循环以同样的5-碳-RuBP分子开始和结束,但这一过程将碳和能量结合成碳氢化合物 — 食物用于生命。

    So – how does photosynthesis store energy in sugar? Six “turns” of the Calvin Cycle use chemical energy from ATP to combine six carbon atoms from six CO 2 molecules with 12 hydrogens from NADPH. The result is one molecule of glucose, C 6 H 12 O 6 .
    ::光合作用如何储存糖的能量? 卡尔文周期的6个“翻转”利用ATP的化学能量将6个二氧化碳分子的6个碳原子与来自NADPH的12个氢分子结合起来。 结果产生了1个葡萄糖分子,C6H12O6。

    Summary
    ::摘要

    • The Calvin Cycle uses the NADPH and ATP from the Light Reactions to “fix” carbon and produce glucose.
      ::Calvin Ccycle使用从轻反应到“固定”碳和生产葡萄糖的NADPH和ATP。
    • Carbon dioxide enters the Calvin Cycle when Rubisco attaches it to a 5-carbon sugar.
      ::当鲁比斯科将二氧化碳附在5碳糖上时,二氧化碳进入卡尔文循环。
    • Most plants fix CO 2 directly with the Calvin Cycle, so they are called C-3 plants.
      ::大部分植物直接用Calvin Ccycle 来修补二氧化碳 所以它们被称为C -3工厂
    • Some plants have evolved preliminary fixation pathways, which help them conserve water in hot, dry habitats.
      ::一些植物已发展出初步固定路径,有助于它们保护炎热干燥生境的水。
    • C-4 plants use a 3-carbon carrier to compartmentalize initial carbon fixation in order to concentrate CO 2 before sending it on to Rubisco.
      ::C-4工厂使用一个三碳载体对初始碳固碳进行分割,以便在将二氧化碳送往Rubisco之前将其浓缩为二氧化碳。
    • CAM plants open their stomata for preliminary CO 2 fixation only at night.
      ::CAM工厂只在夜间打开其stomata, 以便初步固化二氧化碳。
    • In the Calvin Cycle, the fixed CO 2 moves through a series of chemical reactions, gaining a small amount of energy from ATP or NADPH at each step.
      ::在卡尔文循环中,固定的二氧化碳通过一系列化学反应移动,每一步从ATP或NADPH获得少量能量。
    • Six turns of the cycle process 6 molecules of carbon dioxide and 12 hydrogens to produce a single molecule of glucose.
      ::循环过程的六轮 6个二氧化碳分子和12个氢分子 产生单一的葡萄糖分子

    Review
    ::回顾

    1. Match the major events with the stage of photosynthesis (Light Reactions or Calvin Cycle) in which they occur.
      1. Carbon dioxide is fixed.
        ::二氧化碳是固定的。
      2. Electrons in chlorophyll jump to higher energy levels.
        ::叶绿素中的电子 跳升到更高的能量水平
      3. Glucose is produced.
        ::生产甘蔗。
      4. NADPH and ATP are produced.
        ::制作了NADPH和ATP。
      5. NADPH and ATP are used.
        ::使用了NADPH和ATP。
      6. Oxygen gas is released.
        ::氧气释放
      7. Water is split.
        ::水是分开的。

      ::将重大事件与发生这些事件的光合作合(光电反应或卡尔文循环)阶段相匹配; 固化二氧化碳; 叶绿素中的电子跳升到更高的能源水平; 生产甘蔗; 生产NADPH和ATP; 使用NADPH和ATP; 释放氧气; 水分。
    2. Explain the value of cycles of chemical reactions, such as the Calvin Cycle.
      ::解释化学反应周期(如卡尔文周期)的价值。
    3. Define carbon fixation.
      ::定义碳固定。
    4. Explain how their various methods of carbon fixation adapt C-3, C-4, and CAM plants to different habitats.
      ::解释它们的碳固定方法如何使C-3、C-4和CAM工厂适应不同的生境。