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  • Krebs 循环周期

    What will you learn
    ::你会学到什么

    • The role of the Krebs cycle in
      ::Krebs 周期的作用

    Various citrus fruits including oranges, lemons, and limes.

    What type of acid do these fruits contain?
    ::这些水果含有哪种酸?

    Citric acid. Citric acid is also the first product formed in the Krebs cycle, and therefore this acid occurs in the metabolism of virtually all living things.
    ::酸也是Krebs循环中形成的第一个产品,因此,这种酸存在于几乎所有生物的代谢中。

    Cellular Respiration Stage II: The Krebs Cycle
    ::细胞呼吸第二阶段:Krebs循环

    Recall that , stage I of cellular respiration, produces two molecules of pyruvate (also known as pyruvic acid ). These molecules enter the matrix of a , where they start the Krebs cycle . The reactions that occur next are shown in the Figure .
    ::回顾细胞呼吸的第一阶段,即细胞呼吸的第一阶段,产生两种微积酸的分子(也称为pyruvic酸)。这些分子输入一个分子的矩阵,开始 Krebs 循环。下一种反应在图中显示。

    The Krebs cycle, showing carbon atom transformations and energy molecule production.
    The Krebs Cycle

    The Krebs cycle starts with pyruvate from glycolysis. Each small circle in the diagram represents one carbon atom. For example, citric acid is a six-carbon molecule, and OAA (oxaloacetate) is a four-carbon molecule. Follow what happens to the carbon atoms as the cycle proceeds. In one turn through the cycle, how many molecules are produced of ATP ? How many molecules of NADH and FADH 2 are produced?
    ::Krebs 周期从 glyculization 的速流开始。 图表中的每个小圆圈代表一个碳原子。 例如, 柠檬酸是一个六碳分子, OAA( oxloacetate) 是一个四碳分子。 随着循环的不断演进, 跟踪碳原子发生的情况。 在循环的一个转折中, ATP 生成了多少个分子? NADH 和 FADH2 的分子产生了多少 ?

    Before the Krebs cycle begins, pyruvate, which has three carbon atoms, is split apart and combined with an enzyme known as CoA, which stands for coenzyme A. The product of this reaction is a two-carbon molecule called acetyl-CoA. The third carbon from pyruvate combines with oxygen to form carbon dioxide, which is released as a waste product. High-energy electrons are also released and captured in NADH.
    ::在Krebs周期开始之前,具有三个碳原子的回旋剂被拆分,与一种称为CoA的酶(CoA)合二为一,该酶代表Coazyme A。 这种反应的产物是一种双碳分子,叫做乙酰CoA。 蒸发剂的第三个碳与氧合二为一,形成二氧化碳,作为废物释放出来。 高能电子也在NADH中释放并捕捉。

    Steps of the Krebs Cycle
    ::Krebs 周期步骤

    The Krebs cycle itself actually begins when acetyl-CoA combines with a four-carbon molecule called OAA (oxaloacetate) (see the Figure ). This produces citric acid, which has six carbon atoms. This is why the Krebs cycle is also called the citric acid cycle.
    ::Krebs 循环本身实际上始于乙酰碳酸与四碳分子OAA(oxaloacetate)(见图)结合时(见图 ) 。 这会产生柠檬酸, 它有六个碳原子。 这就是为什么Krebs循环也被称为柠檬酸循环的原因。

    After citric acid forms, it goes through a series of reactions that release energy . The energy is captured in molecules of NADH, ATP, and FADH 2 , another energy-carrying compound. Carbon dioxide is also released as a waste product of these reactions.
    ::在柠檬酸形式之后,它经历了释放能量的一系列反应。 能量被NADH、ATP和FADH2的分子所捕捉。 另一种含有能量的化合物。 二氧化碳也作为这些反应的废物产物释放出来。

    The final step of the Krebs cycle regenerates OAA, the molecule that began the Krebs cycle. This molecule is needed for the next turn through the cycle. Two turns are needed because glycolysis produces two pyruvate molecules when it splits glucose .
    ::Krebs 循环周期的最后一步是 OAA , 开始 Krebs 循环的分子 。 此分子在周期的下个转弯时需要该分子。 需要两个转弯, 因为它在分裂葡萄糖时会产生两个闪烁分子 。

    Results of the Krebs Cycle
    ::Krebs 周期结果

    After the second turn through the Krebs cycle, the original glucose molecule has been broken down completely. All six of its carbon atoms have combined with oxygen to form carbon dioxide. The energy from its chemical bonds has been stored in a total of 16 energy-carrier molecules. These molecules are:
    ::在第二次翻转 Krebs 周期后, 原葡萄糖分子已经完全分解。 其全部六个碳原子都与氧合在一起形成二氧化碳。 化学键的能量已经储存在总共16个能量载体分子中。 这些分子是:

    • 4 ATP (including 2 from glycolysis)
      ::4 ATP(包括2个来自水解)
    • 10 NADH (including 2 from glycolysis)
      ::10 NADH(包括2个来自水解)
    • 2 FADH 2
      ::2名FADH2
    DID YOU KNOW?
    The Krebs cycle is an important process not just for cellular respiration. The intermediate compounds in the Krebs cycle are used in the synthesis of other important biomolecules like amino acids and fatty acids .

     

     

     

     

    Summary
    ::摘要

    • The Krebs cycle is the second stage of cellular respiration.
      ::Krebs循环是细胞呼吸的第二阶段。
    • During the Krebs cycle, energy stored in pyruvate is transferred to NADH and FADH 2 , and some ATP is produced.
      ::在Krebs循环周期期间,储存在火速中的能源被转移到NADH和FADH2,并生产了一些ATP。

    Review
    ::回顾

    1. What is the Krebs cycle?
      ::什么是Krebs周期?
    2. What are the products of the Krebs cycle?
      ::Krebs周期的产品是什么?
    3. Explain why two turns of the Krebs cycle are needed for each molecule of glucose.
      ::解释为什么每个葡萄糖分子都需要两轮的Krebs周期。