章节大纲

  • 常规

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  • 酶

    Black and white portrait of American chemist James Sumner.

    What did he discover?
    ::他发现了什么?

    The first enzyme to be isolated was discovered in 1926 by American chemist James Sumner, who crystallized the . The enzyme was urease, which catalyzes the hydrolytic decomposition of urea, a component of urine, into ammonia and carbon dioxide.
    ::美国化学家James Sumner于1926年发现了第一种隔离酶,他将这种酶结晶。酶是泌尿素,它催化尿液分解成氨和二氧化碳,尿液中的尿分解成分。

    H 2 NCONH 2 ( a q ) + H 2 O ( l ) → urease 2 NH 3 ( g ) + CO 2 ( g )

    ::H2NCONH2(aq)+H2O(l)`urserance2NH3(g)+CO2(g)+CO2(g)

    His discovery was ridiculed at first because nobody believed that enzymes would behave the same way that other chemicals did. Sumner was eventually proven right and won the Nobel Prize in Chemistry in 1946.
    ::起初,他的发现被嘲笑,因为没有人相信酶会像其他化学物质那样行事。 萨姆纳最终被证明是正确的,并在1946年获得了诺贝尔化学奖。

    Enzymes
    ::酶

    An enzyme is a protein that acts as a biological . Recall that a catalyst is a substance that increases the rate of a without itself being consumed in the reaction. Cellular processes consist of many chemical reactions that must occur quickly in order for the cell to function properly. Enzymes catalyze most of the chemical reactions that occur in a cell. A substrate is the molecule or molecules on which the enzyme acts. In the urease catalyzed reaction above, urea is the substrate. Figure diagrams a typical enzymatic reaction.
    ::酶是一种作为生物的蛋白质。 提醒注意催化剂是一种物质,它会提高一种物质的速度, 而不会在反应中消耗它本身。 细胞过程包括许多必须迅速发生的化学反应, 以便细胞正常运转。 酶催化了细胞中发生的大部分化学反应。 基质是酶作用的分子或分子。 在以上泌尿酶催化反应中, 尿素是基质。 图显示典型的酶反应。

    Sequence of steps showing substrate binding, reaction, and product release in enzyme catalysis.

    The sequence of steps for a substrate binding to an enzyme in its active site, reacting, then being released as products.
    ::固定在活性网站的酶基质的序列步骤,反应,然后作为产品释放。

    The first step in the reaction is that the substrate binds to a specific part of the enzyme molecule. The binding of the substrate is dictated by the shape of each molecule. Side chains on the enzyme interact with the substrate in a specific way, resulting in the making and breaking of bonds. The active site is the place on an enzyme where the substrate binds. An enzyme folds in such a way that it typically has one active site, usually a pocket or crevice formed by the folding pattern of the protein. Because the active site of an enzyme has such a unique shape, only one particular substrate is capable of binding to that enzyme. In other words, each enzyme catalyzes only one chemical reaction with only one substrate. Once the enzyme/substrate complex is formed, the reaction occurs and the substrate is transformed into products. Finally, the product molecule or molecules are released from the active site. Note that the enzyme is left unaffected by the reaction and is now capable of catalyzing the reaction of another substrate molecule.
    ::反应的第一个步骤是基质与酶分子的特定部分结合。 基质的结合是由每个分子的形状决定的。 酶的侧链以特定的方式与基质相互作用, 导致债券的制作和破碎。 活动地点是基质结合的酶。 酶折叠的方式通常有一个活跃的站点, 通常是由蛋白折叠模式形成的口袋或裂缝。 由于酶的活性站点有这样一个独特的形状, 只有一个特定的基质能够与酶结合。 换句话说, 每种酶只用一个基质催化一种化学反应。 一旦酶/ 基质组合形成, 反应就会发生, 基质变成产品。 最后, 产品分子或分子从活跃的站点释放出来。 注意酶不受反应的影响, 现在能够催化另一个基质的反应。

    Inhibitors
    ::租赁者

    An inhibitor is a molecule which interferes with the function of an enzyme, either by slowing or stopping the chemical reaction. Inhibitors can work in a variety of ways, but one of the most common is illustrated in  Figure .
    ::抑制剂是一种分子,通过减慢或停止化学反应来干扰酶的功能。 抑制剂可以多种方式发挥作用,但最常见的一种表现在图中。

    Diagram illustrating competitive inhibition in enzyme reactions, showing substrate binding prevention.

    A competitive inhibitor is a molecule that binds to the active site of an enzyme without reacting, thus preventing the substrate from binding.
    ::具有竞争力的抑制剂是一种分子,它与酶的活性地点结合,没有反应,从而阻止基质的结合。

    The inhibitor binds competitively at the active site and blocks the substrate from binding. Since no reaction occurs with the inhibitor, the enzyme is prevented from catalyzing the reaction. Cyanide is a potent poison which acts as a competitive inhibitor. It binds to the active site of the enzyme cytochrome c oxidase and interrupts cellular respiration. The binding of the cyanide to the enzyme is irreversible and the affected organism dies quickly.
    ::抑制剂在活性现场具有竞争力,并阻断基质。由于抑制剂不会发生反应,因此酶无法刺激反应。氰化物是一种作为竞争性抑制剂的强效毒物。它与酶细胞分裂酶的活性现场有约束力,并阻断细胞呼吸。氰化物与酶的结合是不可逆的,受影响的有机体迅速死亡。

    Non-competitive Inhibition
    ::非竞争性煽动

    A non-competitive inhibitor does not bind at the active site. It attaches at some other site on the enzyme and changes the shape of the protein. This shift in three-dimensional structure alters the shape of the active site so that the substrate will no longer fit in the site properly (see Figure ).
    ::非竞争抑制剂在活性场地上不固定,它在酶上附着在其他一些场地上,并改变蛋白质的形状。三维结构的这种变化改变了活性场地的形状,使基质不再适合该场地(见图 )。

    Non-competitive inhibition mechanisms in enzyme activity.

    Non-competitive inhibition
    ::非竞争抑制

    Co-factors
    ::共同要素

    Some enzymes require the presence of a non-protein molecule called a cofactor in order to function properly. Cofactors can be inorganic metal or small organic molecules. Many vitamins, such as B vitamins, act as cofactors. Some metal ions which function as cofactors for various enzymes include zinc, magnesium, potassium, and iron.
    ::有些酶需要有一种叫同源物的非蛋白分子才能正常运转。共源物可以是无机金属或小有机分子。许多维他命,如B维他命,作为同源物。一些金属离子作为各种酶的同源物,包括锌、镁、钾和铁。

     

     

    Science Friday : Stained Glass Conservation
    ::星期五:染色玻璃保护

    Stained glass from the Middle Ages is often hundreds of years old. Unfortunately, many of these relics are in need of cleaning and maintenance. In this video by Science Friday , conservator Mary Higgins discusses the methods used to protect the stained glass.
    ::中世纪的染色玻璃往往有数百年的历史。 不幸的是,许多这些遗迹需要清理和维护。 在科学星期五的录像中,玛丽·希金斯(Mary Higgins)讨论了保护染色玻璃的方法。

     

    Review
    ::回顾

    1. What is the substrate?
      ::什么是基质?
    2. How does a competitive inhibitor work?
      ::竞争抑制剂如何运作?
    3. How does a non-competitive inhibitor work?
      ::非竞争抑制剂如何运作?