📚 Enzymes: The Biological Catalysts | 酶：生物催化剂
Enzymes are biological molecules that speed up chemical reactions in living organisms. They are essential for life, enabling processes such as digestion, respiration, and DNA replication to occur at rates compatible with the organism’s survival.
酶是生物分子，能够加速生命体内的化学反应。它们对生命至关重要，使消化、呼吸和DNA复制等过程以与生物体生存相适应的速率进行。
1. What are Enzymes? | 什么是酶？
Enzymes are proteins that act as catalysts. A catalyst is a substance that increases the rate of a chemical reaction without being used up or permanently changed during the process.
酶是作为催化剂起作用的蛋白质。催化剂是一种能提高化学反应速率而自身在反应过程中不被消耗或永久改变的物质。
Each enzyme is specific to a particular reaction or group of reactions. This means that one enzyme usually catalyses only one kind of chemical change.
每种酶对特定反应或一组反应具有特异性。这意味着一种酶通常只催化一种化学变化。
For example, the enzyme amylase breaks down starch into maltose, while protease breaks down proteins into amino acids. These reactions would be very slow without enzymes.
例如，淀粉酶将淀粉分解为麦芽糖，而蛋白酶将蛋白质分解为氨基酸。没有酶，这些反应会非常缓慢。
2. Structure of Enzymes | 酶的结构
Enzymes are made of long chains of amino acids folded into a specific three-dimensional shape. The shape is critical for the enzyme’s function.
酶由长链氨基酸折叠成特定的三维形状。该形状对酶的功能至关重要。
Most enzymes have a region called the active site, which is the part of the enzyme where the substrate binds. The active site has a shape complementary to the substrate.
大多数酶有一个称为活性中心的区域，即底物与酶结合的部位。活性中心的形状与底物互补。
Because the active site is specific, only certain substrates can fit into it. Any change in the enzyme’s shape can affect its ability to bind the substrate.
由于活性中心具有特异性，只有特定底物才能与之匹配。酶形状的任何变化都会影响其结合底物的能力。
3. The Lock and Key Hypothesis | 锁钥假说
The lock and key hypothesis describes how an enzyme and substrate interact. The enzyme is the lock, and the substrate is the key. Only the correct key can fit into the lock.
锁钥假说描述了酶与底物如何相互作用。酶是锁，底物是钥匙。只有正确的钥匙才能插入锁中。
When the substrate binds to the active site, an enzyme-substrate complex is formed. The reaction then takes place, and the products are released.
当底物与活性中心结合时，形成酶-底物复合物。随后反应发生，产物被释放出来。
The enzyme itself remains unchanged and can be reused for further reactions.
酶本身保持不变，并能被重复用于后续反应。
4. Factors Affecting Enzyme Activity: Temperature | 影响酶活性的因素：温度
Temperature has a significant effect on enzyme activity. As temperature increases, the particles move faster and collide more often, so the rate of reaction increases.
温度对酶活性有显著影响。温度升高时，粒子运动更快，碰撞更频繁，因此反应速率增大。
However, very high temperatures cause the enzyme to denature. The bonds holding the enzyme’s structure break, changing the shape of the active site.
然而，过高温度会导致酶变性。维持酶结构的化学键断裂，改变了活性中心的形状。
When an enzyme is denatured, it can no longer bind to its substrate, and its catalytic activity is lost permanently.
当酶变性时，它不能再与底物结合，其催化活性永久丧失。
For most human enzymes, the optimum temperature is around 37°C, which is the normal body temperature.
大多数人体酶的适宜温度约为37°C，即正常体温。
5. Factors Affecting Enzyme Activity: pH | 影响酶活性的因素：pH
Every enzyme has an optimum pH at which it works best. In the human body, many enzymes work best at pH 7, which is neutral.
每种酶均有其最适pH值，在此pH下活性最高。在人体内，许多酶在pH 7（即中性）时活性最佳。
For example, pepsin, a digestive enzyme in the stomach, works best at pH 2, a very acidic environment.
例如，胃中的消化酶胃蛋白酶在pH 2（强酸性环境）时活性最佳。
If the pH changes significantly, the enzyme can denature. The hydrogen ion concentration affects the charge and shape of the active site.
如果pH发生显著变化，酶可能变性。氢离子浓度影响活性中心的电荷和形状。
6. Factors Affecting Enzyme Activity: Substrate Concentration | 影响酶活性的因素：底物浓度
As the substrate concentration increases, the rate of reaction also increases because the chances of the enzyme colliding with substrate molecules are higher.
随着底物浓度升高，反应速率也增大，因为酶与底物分子碰撞的概率更高。
However, this increase continues only up to a certain point. At high substrate concentrations, all the active sites of the enzyme molecules are occupied.
然而，这种增长只持续到一定限度。在高底物浓度下，酶分子的所有活性中心都被占据。
When all active sites are full, the reaction rate reaches its maximum and cannot increase further. This is known as a plateau, or Vmax.
当所有活性中心都占满时，反应速率达到最大值，无法进一步增加。这称为平台期或最大速率（Vmax）。
7. Enzyme Inhibition | 酶抑制
Some substances can reduce the activity of enzymes. These are called inhibitors. Inhibitors can be competitive or non-competitive.
有些物质能降低酶的活性，称为抑制剂。抑制剂可分为竞争性抑制和非竞争性抑制。
Competitive inhibitors compete with the substrate for the active site. They have a similar shape to the substrate, so they can block the active site.
竞争性抑制剂与底物竞争活性中心。它们具有与底物相似的形状，因此能占据活性中心。
Non-competitive inhibitors bind to parts of the enzyme other than the active site. This changes the shape of the active site, making it unable to accept the substrate.
非竞争性抑制剂结合到酶上活性中心以外的部位，这会改变活性中心的形状，使其无法接纳底物。
8. Applications of Enzymes | 酶的应用
Enzymes are widely used in industry and medicine. For example, in the production of bread, the enzyme amylase breaks down starch into sugars for the yeast to ferment.
酶在工业和医学领域广泛使用。例如，在面包制作中，淀粉酶将淀粉分解为糖，供酵母发酵。
Proteases are used in biological detergents to remove protein stains. Lipases are used to break down fats in some waste-processing systems.
蛋白酶用于生物洗涤剂中去除蛋白质污渍。脂肪酶用于某些废物处理系统中分解脂肪。
Lactase is used to produce lactose-free milk for people who are lactose intolerant. This shows the practical importance of enzymes.
乳糖酶用于为乳糖不耐受人群生产无乳糖牛奶。这显示了酶的实际重要性。
9. Investigating Enzyme Activity | 探究酶活性
Enzyme activity can be investigated in the laboratory using simple experiments. One common experiment involves catalase and hydrogen peroxide.
酶活性可以在实验室中通过简单实验进行探究。常见实验涉及过氧化氢酶和过氧化氢。
Catalase breaks down hydrogen peroxide into water and oxygen gas. The rate of oxygen bubble production indicates the rate of the reaction.
过氧化氢酶将过氧化氢分解为水和氧气。产生氧气气泡的速率可指示反应速率。
By changing the temperature or pH, students can observe how the rate changes. This helps confirm the factors discussed above.
通过改变温度或pH，学生可以观察反应速率如何变化，这有助于确认上述所讨论的因素。
Published by TutorHao | Science Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
屏轩国际教育cambridge primary/secondary checkpoint, cat4, ukiset,ukcat,igcse,alevel,PAT,STEP,MAT, ibdp,ap,ssat,sat,sat2课程辅导，国外大学本科硕士研究生博士课程论文辅导Cancel reply