📚 748 – Enzymes and Their Role in Biological Reactions | 748 – 酶及其在生物反应中的作用
Enzymes are biological catalysts made of protein that speed up almost every chemical reaction inside living organisms. Without enzymes, metabolism would be far too slow to sustain life. In IGCSE Edexcel Science, you must understand how enzymes work, the factors influencing their activity, and their importance in processes such as digestion and industry.
酶是由蛋白质组成的生物催化剂，能够加速生物体内几乎所有的化学反应。如果没有酶，新陈代谢的速度将过慢而无法维持生命。在 IGCSE 爱德思科学课程中，你必须理解酶的工作原理、影响其活性的因素以及它们在消化和工业等过程中的重要性。
1. What Are Enzymes? | 什么是酶？
Enzymes are large protein molecules that act as catalysts. A catalyst is a substance that increases the rate of a chemical reaction without being used up or changed permanently. Enzymes lower the activation energy needed for a reaction to occur, meaning less energy is required to start the reaction. Each enzyme has a specific three‑dimensional shape, including a region called the active site.
酶是作为催化剂发挥作用的大型蛋白质分子。催化剂能够增加化学反应速率，而自身不会被消耗或永久改变。酶降低了反应所需的活化能，这意味着启动反应所需的能量更少。每一种酶都有独特的三维形状，其中包括一个称为活性位点的区域。
2. The Lock and Key Model | 锁钥模型
The ‘lock and key’ model is used to explain enzyme action. In this model, the active site of the enzyme (the lock) is precisely shaped to fit a specific substrate molecule (the key). When the substrate binds to the active site, an enzyme‑substrate complex forms. The reaction then takes place rapidly, and the product or products are released, leaving the enzyme unchanged and ready to bind another substrate molecule.
“锁钥”模型用来解释酶的作用方式。在这一模型中，酶的活性位点（锁）具有精确的形状，可与特定的底物分子（钥匙）相契合。当底物与活性位点结合时，形成酶‑底物复合物。随后反应快速进行，产物被释放出来，酶本身未发生改变，并可再次结合另一个底物分子。
3. Enzyme Specificity | 酶的特异性
Enzymes are highly specific – each type of enzyme usually catalyses only one particular reaction or a group of very similar reactions. This is because the active site has a unique shape and chemical properties that only allow one type of substrate to fit. For example, the enzyme amylase only breaks down starch into maltose; it cannot work on proteins or lipids.
酶具有高度特异性——每种酶通常只催化一种特定的反应或一组非常相似的反应。这是因为活性位点具有独特的形状和化学特性，只允许一种类型的底物与之结合。例如，淀粉酶只能将淀粉分解为麦芽糖，无法作用于蛋白质或脂类。
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 the temperature rises, the kinetic energy of molecules increases, leading to more frequent collisions between enzyme and substrate. Therefore, the rate of reaction increases up to an optimum temperature (around 37 °C for many human enzymes). Beyond this optimum, the enzyme protein begins to lose its shape, and the active site becomes distorted – this is called denaturation. Once denatured, the enzyme can no longer function, and the rate of reaction drops sharply.
温度对酶活性有显著影响。随着温度升高，分子动能增加，酶与底物之间的碰撞更加频繁。因此，反应速率会上升，直至达到最适温度（很多人体酶的约为37 °C）。超过最适温度后，酶蛋白开始失去其原有形状，活性位点发生扭曲——这就是变性。一旦变性，酶便无法再起作用，反应速率急剧下降。
5. Factors Affecting Enzyme Activity: pH | 影响酶活性的因素：pH
The pH of the environment also affects enzyme activity. Every enzyme has an optimum pH at which it works most efficiently. For most enzymes in the human body, this is around pH 7. However, some enzymes work in very different conditions, such as pepsin in the stomach, which has an optimum pH of about 2. Extreme pH values (too acidic or too alkaline) can disrupt the bonds that hold the enzyme’s shape, leading to denaturation and loss of function.
环境的pH值同样影响酶活性。每一种酶都有其最适pH，在该pH下其工作效率最高。人体内大多数酶的最适pH在7左右。但是，有些酶在差异极大的条件下工作，例如胃蛋白酶的最适pH约为2。极端的pH值（过酸或过碱）会破坏维持酶形状的化学键，导致变性并丧失功能。
6. Denaturation of Enzymes | 酶的变性
Denaturation is the permanent change in the shape of an enzyme’s active site caused by high temperature or unfavourable pH. When an enzyme is denatured, the substrate can no longer fit into the active site, so the enzyme‑substrate complex cannot form. Because denaturation is usually irreversible, the catalytic function is permanently lost. This is why high fevers or strong acids can be very harmful to living cells.
变性是指由于高温或不利的pH导致酶活性位点的形状发生永久性改变。当酶变性后，底物无法再嵌入活性位点，酶‑底物复合物便不能形成。由于变性通常是不可逆的，酶的催化功能永久丧失。这就是为什么高烧或强酸会对活细胞造成极大危害的原因。
7. Enzymes in Digestion | 消化过程中的酶
Digestive enzymes are crucial for breaking down large, insoluble food molecules into smaller, soluble ones that can be absorbed into the blood. Key examples include:
消化酶对于将大分子、不溶性的食物分解成可吸收进入血液的小分子可溶物质至关重要。关键的例子包括：
| Enzyme (酶) | Substrate (底物) | Product(s) (产物) |
| Amylase (淀粉酶) | Starch (淀粉) | Maltose (麦芽糖) |
| Protease (蛋白酶) | Proteins (蛋白质) | Amino acids (氨基酸) |
| Lipase (脂肪酶) | Lipids (fats) (脂类/脂肪) | Glycerol + fatty acids (甘油 + 脂肪酸) |
Amylase is produced in the salivary glands and pancreas, protease in the stomach and pancreas, and lipase in the pancreas. Bile, although not an enzyme, helps by emulsifying fats to increase the surface area for lipase action.
淀粉酶由唾液腺和胰腺分泌，蛋白酶由胃和胰腺分泌，脂肪酶由胰腺分泌。胆汁虽然不是酶，但能通过乳化脂肪增大脂肪酶作用的表面积。
8. Practical Investigation of Enzyme Activity | 酶活性的实验探究
A common IGCSE practical involves investigating the effect of temperature on amylase activity. Starch solution is mixed with amylase at a set temperature, and samples are taken every few seconds to test with iodine solution. When the iodine no longer turns blue‑black, all the starch has been broken down into maltose, and the time taken is recorded. Repeating this at different temperatures allows you to plot a graph of rate against temperature, showing the optimum temperature and the point of denaturation.
一个常见的IGCSE实验是探究温度对淀粉酶活性的影响。在设定温度下将淀粉溶液与淀粉酶混合，每隔几秒钟取样并用碘液测试。当碘液不再变为蓝黑色时，说明所有淀粉都已分解成麦芽糖，记录所需时间。在不同温度下重复该实验，可绘制反应速率-温度关系图，显示出最适温度和变性点。
9. Uses of Enzymes in Industry and Medicine | 酶在工业及医学中的应用
Enzymes are widely used outside living cells. In the food industry, proteases and lipases are found in biological washing powders to break down stains. Lactase is used to produce lactose‑free milk. In medicine, enzymes are used in diagnostic test strips, and genetically engineered enzymes help treat diseases. Their ability to work at relatively low temperatures and produce few unwanted by‑products makes them environmentally friendly catalysts.
酶在活细胞外也有着广泛的应用。在食品工业中，生物洗衣粉含有蛋白酶和脂肪酶，用以分解污渍。乳糖酶被用来生产无乳糖牛奶。在医学中，酶被用于诊断试纸，基因工程改造的酶则可用于治疗疾病。酶能够在相对较低的温度下工作并且产生很少的不需要的副产物，这使它们成为了环保型催化剂。
10. Key Points to Remember | 需要牢记的要点
- Enzymes are proteins that act as biological catalysts – they speed up reactions without being consumed.
- 酶是蛋白质，作为生物催化剂——它们在加快反应的同时本身不被消耗。
- The active site is specific to one substrate; the lock and key model explains this complementary shape.
- 活性位点对某种底物具有特异性；锁钥模型解释这种形状互补机制。
- Temperature and pH must be controlled – extreme values cause denaturation, which is often irreversible.
- 温度和pH必须加以控制——极端值会引起变性，这往往是不可逆的。
- Digestive enzymes break down large molecules; amylase, protease and lipase are key examples.
- 消化酶分解大分子；淀粉酶、蛋白酶和脂肪酶是典型例子。
- Enzymes are used in industry and medicine, from washing powders to lactose‑free products.
- 酶被应用于工业和医学领域，从洗衣粉到无乳糖产品均有涉及。
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