📚 Enzymes: Biological Catalysts | 酶：生物催化剂
Enzymes are the engines of life. Without them, the chemical reactions that sustain every living cell would be far too slow to support existence. This article unpacks the structure, models, factors, and real-world applications of enzymes, providing a complete revision resource for Edexcel IGCSE Science students.
酶是生命的引擎。没有它们，维持每个活细胞所需的化学反应就会过慢，根本无法支撑生命。本文解析酶的结构、作用模型、影响因素以及实际应用，为Edexcel IGCSE科学考生提供一份完整的复习资料。
1. What Are Enzymes? | 什么是酶？
Enzymes are globular proteins that function as biological catalysts. A catalyst is a substance that speeds up a chemical reaction without being used up or changed permanently. In living organisms, enzymes lower the activation energy needed for metabolic reactions, allowing processes such as respiration, photosynthesis and digestion to occur rapidly at relatively low temperatures.
酶是球状蛋白质，作为生物催化剂发挥作用。催化剂是一种能加速化学反应而自身不被消耗或永久改变的物质。在生物体内，酶能降低代谢反应所需的活化能，使呼吸、光合作用和消化等过程能在相对较低的温度下迅速进行。
Each enzyme is specific to a particular substrate, meaning it will only catalyse one type of reaction. The name of an enzyme often ends in '-ase' and hints at its substrate, for example, maltase breaks down maltose, protease digests protein and lipase targets lipids.
每种酶对特定的底物具有专一性，也就是说它只催化某一类型的反应。酶的名称通常以“酶(-ase)”结尾，并暗示其底物，例如：麦芽糖酶分解麦芽糖，蛋白酶消化蛋白质，脂肪酶作用于脂类。
2. Enzyme Structure and the Active Site | 酶的结构与活性部位
Enzymes are made of long chains of amino acids folded into a precise three-dimensional shape. This folding creates a region called the active site, which is a cleft or pocket with a shape and chemical properties that perfectly complement the substrate molecule. The structure of the active site is maintained by hydrogen bonds, ionic interactions and hydrophobic effects that stabilise the tertiary structure of the protein.
酶由长链氨基酸折叠成精确的三维结构。这种折叠形成一个称为活性部位的区域，它是一座凹陷或口袋，其形状和化学性质与底物分子完美互补。活性部位的结构由氢键、离子相互作用和疏水效应来维持，它们稳定了蛋白质的三级结构。
If the shape of the active site is altered, the enzyme can no longer bind to its substrate and loses its catalytic function. This is why enzymes are sensitive to changes in temperature and pH.
如果活性部位的形状发生改变，酶就再也无法与底物结合，失去催化功能。这就是酶对温度和pH变化敏感的原因。
3. The Lock and Key Model | 锁钥模型
The lock and key model was proposed by Emil Fischer in 1894. It suggests that the active site has a fixed, rigid shape that is exactly complementary to the shape of the substrate, much like a key fits into a specific lock. The substrate slots into the active site, forming an enzyme-substrate complex, where the reaction takes place.
锁钥模型由埃米尔·费歇尔于1894年提出。该模型认为活性部位具有固定、刚性的形状，恰好与底物的形状互补，就像一把钥匙插入特定的锁。底物嵌入活性部位，形成酶-底物复合物，反应便在此处发生。
While this model explains enzyme specificity elegantly, it does not account for the flexibility of the enzyme molecule observed in many experiments.
尽管这个模型精巧地解释了酶的专一性，但它无法解释许多实验中观察到的酶分子的柔性。
4. The Induced Fit Model | 诱导契合模型
The induced fit model, refined by Daniel Koshland in 1958, provides a more accurate picture. According to this model, the active site is not rigid. Instead, when the substrate approaches, the active site undergoes a slight conformational change to mould itself around the substrate. This induced fit strains chemical bonds in the substrate, lowering the activation energy even further and facilitating the reaction.
由丹尼尔·科什兰于1958年完善的诱导契合模型给出了更准确的描述。根据该模型，活性部位并非刚性。当底物靠近时，活性部位会发生轻微的构象变化，将自己贴合在底物周围。这种诱导契合使底物中的化学键受到应力，进一步降低活化能，从而促进反应。
The model highlights the dynamic nature of protein structure and explains how some enzymes can accept a small range of structurally similar substrates while remaining highly specific.
该模型突显了蛋白质结构的动态本质，并解释了为何某些酶能在保持高度专一性的同时，接纳一小类结构相似的底物。
5. Factors Affecting Enzyme Activity: Temperature | 影响酶活性的因素：温度
Temperature has a profound effect on enzyme-catalysed reactions. As the temperature increases, the kinetic energy of enzyme and substrate molecules rises, causing more frequent collisions and a greater likelihood of successful enzyme-substrate complex formation. This means the rate of reaction increases, roughly doubling for every 10 °C rise until an optimum temperature is reached.
温度对酶催化反应影响深远。随着温度升高，酶和底物分子的动能增加，导致碰撞更频繁，形成酶-底物复合物的成功率更高。这意味着反应速率上升，大约每升高10 °C，速率就翻倍，直至达到最适温度。
For most human enzymes, the optimum temperature is around 37 °C. Beyond this point, the high temperature disrupts the hydrogen bonds and other interactions holding the tertiary structure together. The active site loses its complementary shape, the enzyme becomes denatured and activity drops sharply.
对人体内大多数酶而言，最适温度约为37 °C。超过这个温度后，高温会破坏维系三级结构的氢键和其他相互作用。活性部位失去互补形状，酶发生变性，活性急剧下降。
6. Factors Affecting Enzyme Activity: pH | 影响酶活性的因素：pH
Enzymes also have an optimum pH at which they work most efficiently. This is because the charges on the amino acid side chains at the active site are influenced by the concentration of hydrogen ions (H⁺). Deviations from the optimum pH alter the ionic bonds that maintain the enzyme's shape, leading to loss of activity and eventual denaturation.
酶也有一个能发挥最高效率的最适pH。这是因为活性部位氨基酸侧链上的电荷受到氢离子(H⁺)浓度的影响。偏离最适pH会改变维持酶形状的离子键，导致活性下降乃至最终变性。
Different enzymes have different pH optima. For example, pepsin, a protease that works in the stomach, has an optimum pH of about 2, while trypsin, which operates in the small intestine, prefers a slightly alkaline pH of around 8.
不同的酶具有不同的最适pH。例如，在胃中工作的胃蛋白酶最适pH约为2，而在小肠中工作的胰蛋白酶则偏好大约8的弱碱性环境。
7. Enzyme Concentration and Substrate Concentration | 酶浓度与底物浓度
Increasing enzyme concentration will raise the rate of reaction, provided there is excess substrate available. Because more active sites are present, more substrate molecules can be converted into product per unit time. The relationship is usually linear until all substrate is bound.
在底物过量的前提下，增加酶浓度会提高反应速率。因为有更多活性部位，单位时间内就能转化更多的底物分子。通常这一关系呈线性，直到所有底物被结合为止。
With substrate concentration, the rate rises steeply at low substrate concentrations and then levels off at a maximum velocity (Vmax). At Vmax, every active site is occupied, and adding more substrate cannot increase the rate further. This saturation effect is a hallmark of enzyme kinetics.
就底物浓度而言，速率在低底物浓度时急剧上升，随后在达到最大速率(Vmax)时趋于平缓。在Vmax时，每个活性部位都被占据，再加入更多底物也无法提高速率。这种饱和效应是酶动力学的标志性特征。
8. Denaturation of Enzymes | 酶的变性
Denaturation is the irreversible change in the three-dimensional shape of an enzyme that destroys its catalytic ability. It can be caused by excessive heat, extreme pH, heavy metal ions such as lead (Pb²⁺) or mercury (Hg²⁺), and organic solvents. Once denatured, even if optimum conditions are restored, the enzyme cannot regain its functional shape because the folding was determined during protein synthesis.
变性是指酶的三维形状发生不可逆变化，从而破坏其催化能力。过量受热、极端pH、铅(Pb²⁺)或汞(Hg²⁺)等重金属离子以及有机溶剂都会引起变性。一旦变性，即使恢复最适条件，酶也无法恢复其功能形状，因为折叠是在蛋白质合成时就被确定了的。
It is important to note that not all shape changes are denaturation. Some enzymes can be temporarily inactivated by cold, but they regain activity on warming.
需要注意的是，并非所有形状变化都是变性。某些酶会被低温暂时钝化，但回暖后能恢复活性。
9. Enzymes in Digestion: Examples | 消化中的酶：举例
The human digestive system relies on a suite of enzymes to hydrolyse large insoluble food molecules into small, soluble ones that can be absorbed.
人体消化系统依赖一整套酶，将大分子不可溶食物水解成可吸收的小分子可溶物质。
| Enzyme | Source | Substrate | Products | pH Optimum |
|---|---|---|---|---|
| Amylase | Salivary glands, pancreas | Starch | Maltose | ~7 |
| Protease (Pepsin) | Stomach | Protein | Polypeptides | ~2 |
| Trypsin | Pancreas | Polypeptides | Shorter peptides | ~8 |
| Lipase | Pancreas | Lipids (fats) | Fatty acids + Glycerol | ~7-8 |
| Maltase | Small intestine wall | Maltose | Glucose | ~7 |
Note that bile is not an enzyme but emulsifies fats, providing a larger surface area for lipase to act upon.
请注意，胆汁不是酶，它通过乳化脂肪为脂肪酶提供更大的作用表面积。
10. Industrial Uses of Enzymes | 酶的工业用途
Enzymes are widely exploited in industry because they operate under mild conditions, are biodegradable, and reduce energy costs. In biological washing powders, proteases and lipases break down protein and fat stains at low temperatures. Amylases are used in bread-making to convert starch into maltose, which yeast then ferments, helping the dough rise.
酶因其在温和条件下工作、可生物降解并能降低能源成本，而在工业上得到广泛应用。在生物洗衣粉中，蛋白酶和脂肪酶在低温下分解蛋白质和脂肪污渍。淀粉酶用于面包制作，将淀粉转化为麦芽糖，再由酵母发酵，帮助面团发起。
In the production of cheese, rennin (chymosin) is used to coagulate milk. In fruit juice manufacturing, pectinase breaks down pectin, making the juice clearer and increasing yield. Isomerase is used to convert glucose into the sweeter fructose in high-fructose corn syrup. Each application relies on careful control of temperature and pH to maintain enzyme activity.
在奶酪生产中，凝乳酶(凝乳素)用于让牛奶凝固。在果汁生产中，果胶酶分解果胶，使果汁更清澈并提高产量。异构酶在果葡糖浆生产中将葡萄糖转化为更甜的果糖。每一项应用都依赖精确控温、控pH来维持酶活性。
11. Practical Investigation: Effect of Temperature on Enzyme Activity | 实验探究：温度对酶活性的影响
A common Edexcel IGCSE practical uses amylase and starch to investigate how temperature affects the rate of reaction. A buffered starch solution is mixed with amylase at a known temperature, and samples are taken at timed intervals, tested with iodine solution. The time taken for the blue-black colour to disappear indicates the breakdown of starch to maltose.
Edexcel IGCSE常见的实验是使用淀粉酶和淀粉来探究温度如何影响反应速率。在已知温度下将缓冲淀粉溶液与淀粉酶混合，每隔一定时间取样，用碘液测试。蓝黑色消失所需的时间即可指示淀粉被分解为麦芽糖的进程。
The independent variable is temperature (e.g., 10 °C, 20 °C, 30 °C, 40 °C, 50 °C, 60 °C). The dependent variable is time for starch disappearance (or rate, calculated as 1/time). Controlled variables include enzyme and substrate concentration, volume, and pH. A graph of rate against temperature will show a peak at the optimum, followed by a sharp decline due to denaturation.
自变量是温度（如10 °C、20 °C、30 °C、40 °C、50 °C、60 °C）。因变量是淀粉消失所需时间（或用其倒数表示速率）。控制变量包括酶和底物浓度、体积以及pH。速率-温度曲线图将在最适温度处出现峰值，随后因变性而急剧下降。
12. Key Definitions and Summary | 关键定义与总结
Key terms for Edexcel IGCSE Science:
Edexcel IGCSE科学关键术语：
- Enzyme: a biological catalyst that is a protein / 酶：一种本质为蛋白质的生物催化剂。
- Active site: region on enzyme where substrate binds / 活性部位：酶上底物结合的区域。
- Substrate: molecule(s) that an enzyme acts on / 底物：酶所作用的分子。
- Denaturation: permanent loss of enzyme shape and function due to extreme conditions / 变性：极端条件导致酶形状和功能的永久丧失。
- Optimum temperature/pH: conditions at which enzyme activity is highest / 最适温度/pH：酶活性最高的条件。
- Lock and key model: rigid active site exactly fits substrate / 锁钥模型：刚性活性部位完全匹配底物。
- Induced fit model: active site changes shape around substrate / 诱导契合模型：活性部位围绕底物改变形状。
Enzymes underpin both life and biotechnology. Mastering how they work, what affects them and how to investigate their activity is essential for the Edexcel IGCSE Science examinations. Remember: specificity, shape and conditions are the keys.
酶是生命和生物技术的基础。掌握酶的作用机制、影响因素以及如何探究酶活性，对于Edexcel IGCSE科学考试至关重要。记住：专一性、形状和条件是关键。
Published by TutorHao | Science Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
或截图后用「扫一扫 → 相册」选择本图