Enzymes: Catalysts of Life | 酶：生命催化剂

📚 Enzymes: Catalysts of Life | 酶：生命催化剂

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 fast enough to sustain metabolism. In the Edexcel IGCSE Science specification, understanding enzymes is a core requirement, and this article will guide you through their structure, function, and real-world applications.

酶是生物分子，能够加速生物体内的化学反应。它们是生命所必需的，使消化、呼吸和DNA复制等过程能够以足够快的速度进行以维持新陈代谢。在爱德思IGCSE科学考试大纲中，理解酶是核心要求，本文将引导你学习它们的结构、功能以及现实应用。

1. What Are Enzymes? | 什么是酶？

Enzymes are proteins that act as biological catalysts. A catalyst is a substance that increases the rate of a chemical reaction without being used up or permanently changed in the process. Each enzyme is specific to one particular reaction or group of reactions because its active site has a unique shape that fits only a certain substrate.

酶是充当生物催化剂的蛋白质。催化剂是一种能够提高化学反应速率，而自身在反应过程中不被消耗或永久改变的物质。每种酶对一种特定的反应或一组反应具有专一性，因为其活性位点具有独特的形状，只能匹配特定的底物。

Enzymes are made up of long chains of amino acids folded into complex three-dimensional shapes. The part of the enzyme where the reaction takes place is called the active site. The ‘lock and key’ model is often used to describe this specificity: the active site is the lock, and the substrate is the key.

酶由长链氨基酸折叠成复杂的三维结构。酶上进行反应的部分称为活性位点。“锁钥模型”常用来描述这种专一性：活性位点是锁，底物是钥匙。

Key terms:

关键术语：

Enzyme – a biological catalyst made of protein.
酶 – 由蛋白质构成的生物催化剂。
Substrate – the molecule that binds to the active site.
底物 – 与活性位点结合的分子。
Active site – the region on the enzyme where catalysis occurs.
活性位点 – 酶上发生催化的区域。
Product – the molecule(s) formed after the reaction.
产物 – 反应后生成的分子。

2. The Lock and Key Model | 锁钥模型

The lock and key model was proposed by Emil Fischer in 1894. It states that the active site of an enzyme has a rigid, fixed shape that is complementary to the shape of the substrate. When the substrate fits into the active site, an enzyme-substrate complex is formed. The reaction then takes place and the products are released, leaving the enzyme unchanged and ready for another substrate molecule.

锁钥模型由埃米尔·费舍尔于1894年提出。该模型认为酶的活性位点具有刚性的、固定的形状，与底物形状互补。当底物与活性位点结合时，形成酶-底物复合物。随后反应发生并释放产物，酶保持不变，可继续催化下一个底物分子。

However, the lock and key model does not explain all observations. A more accurate model is the induced fit model, where the active site changes shape slightly to better accommodate the substrate after binding. This induces strain on the substrate molecule, lowering the activation energy.

然而，锁钥模型不能解释所有现象。更准确的模型是诱导契合模型，即活性位点在底物结合后会发生轻微的形状变化以更好地匹配底物。这将应力作用于底物分子，从而降低活化能。

Enzyme + Substrate → Enzyme-Substrate Complex → Enzyme + Product

酶 + 底物 → 酶-底物复合物 → 酶 + 产物

In both models, the specificity remains: only substrates with the correct shape can bind. This is why enzymes are highly specific.

在这两种模型中，专一性始终存在：只有形状正确的底物才能结合。这就是酶高度专一的原因。

3. Factors Affecting Enzyme Activity | 影响酶活性的因素

Several factors influence how quickly an enzyme catalyses a reaction. The most important factors studied in IGCSE Science are temperature, pH, enzyme concentration, substrate concentration, and inhibitors. These factors can either increase or decrease the rate of reaction, and sometimes they can permanently damage the enzyme.

影响酶催化反应速率的因素有很多。IGCSE科学中研究的最重要的因素包括温度、pH、酶浓度、底物浓度和抑制剂。这些因素可以增加或降低反应速率，有时甚至会永久性地破坏酶。

It is important to distinguish between altering the rate of a reaction and denaturing an enzyme. For example, increasing temperature initially speeds up the reaction, but if the temperature becomes too high, the enzyme denatures and the rate drops sharply to zero.

区分改变反应速率与使酶变性非常重要。例如，升高温度起初会加快反应，但如果温度过高，酶会变性，反应速率会骤降至零。

The rate of an enzyme-controlled reaction can be measured by the volume of product produced per unit time, or by the decrease in substrate concentration over time. In experiments, samples are taken at regular intervals and the rate is calculated from the gradient of a graph.

酶促反应的速率可以通过单位时间内产物的生成量或底物浓度随时间的减少量来测量。在实验中，需定期取样，并从图表斜率计算速率。

4. Temperature and Enzyme Activity | 温度与酶活性

As temperature increases, the kinetic energy of molecules increases, so substrate molecules collide with the active site more frequently and with more energy. This increases the rate of reaction. However, enzymes are proteins, and high temperatures cause the bonds holding the enzyme’s structure together to vibrate and break. The active site loses its shape, and the substrate can no longer bind. The enzyme is said to be denatured.

随着温度升高，分子的动能增加，底物分子与活性位点碰撞更频繁且具有更多能量，从而加快反应。然而，酶是蛋白质，高温会使维持酶结构的化学键振动并断裂。活性位点失去形状，底物无法再结合，这时称酶已变性。

Each enzyme has an optimum temperature, at which its activity is maximum. In the human body, most enzymes have an optimum temperature of around 37°C (body temperature). For example, the enzyme catalase, which breaks down hydrogen peroxide, has an optimum temperature of about 37°C in humans.

每种酶都有一个最适温度，在该温度下其活性最高。在人体内，大多数酶的最适温度约为37°C（体温）。例如，分解过氧化氢的过氧化氢酶，在人体内的最适温度约为37°C。

The graph of enzyme activity against temperature shows a rise to a peak at the optimum temperature, followed by a sharp fall as the enzyme denatures. Denaturation is usually permanent because the change in shape is irreversible.

酶活性对温度的曲线图显示，活性随温度升至最适温度时达到峰值，然后随着酶变性而急剧下降。变性通常是永久性的，因为形状的变化是不可逆的。

5. pH and Enzyme Activity | pH与酶活性

pH is a measure of hydrogen ion concentration. Changes in pH affect the charges on amino acid residues in the enzyme, which can alter the hydrogen bonds and ionic bonds that maintain the enzyme’s three-dimensional structure. If the pH is too high or too low, the active site changes shape and the enzyme denatures.

pH是氢离子浓度的度量。pH的变化会影响酶中氨基酸残基的电荷，从而改变维持酶三维结构的氢键和离子键。如果pH过高或过低，活性位点会改变形状，酶就会变性。

Each enzyme has an optimum pH. For most enzymes in the body, the optimum pH is around 7 (neutral). However, pepsin, an enzyme in the stomach, works best at pH 2, because the stomach is acidic. On the other hand, trypsin, an enzyme in the small intestine, works best at pH 8. This adaptation ensures that each enzyme works where the environment matches its optimum pH.

每种酶都有一个最适pH。体内大多数酶的最适pH约为7（中性）。然而，胃中的胃蛋白酶在pH 2时活性最高，因为胃是酸性的。另一方面，小肠中的胰蛋白酶在pH 8时活性最高。这种适应性保证了每种酶在与其最适pH匹配的环境中发挥作用。

Pepsin: optimum pH ~2 | 胃蛋白酶：最适pH约2

Trypsin: optimum pH ~8 | 胰蛋白酶：最适pH约8

Buffer solutions are used in experiments to keep pH constant. If the pH changes during an experiment, the rate will change, making it difficult to determine the effect of other variables.

在实验中，使用缓冲溶液保持pH恒定。如果实验过程中pH发生变化，速率也会发生变化，从而难以确定其他变量的影响。

6. Enzyme Concentration and Substrate Concentration | 酶浓度与底物浓度

When the substrate concentration is kept constant, increasing the enzyme concentration increases the rate of reaction, provided that there is enough substrate. This is because more active sites are available to bind substrate molecules. However, if the substrate concentration becomes the limiting factor, further increases in enzyme concentration will have no effect.

当底物浓度保持不变时，增加酶浓度会提高反应速率，前提是有足够的底物。这是因为有更多的活性位点可用于结合底物分子。然而，如果底物浓度成为限制因素，继续增加酶浓度将不再有影响。

Similarly, when the enzyme concentration is constant, increasing the substrate concentration initially increases the rate of reaction. As more substrate molecules are present, there is a higher chance of collisions with active sites. However, at some point, all the active sites are occupied, and the enzyme is said to be saturated. The rate of reaction reaches a maximum and cannot increase further, no matter how much more substrate is added.

同样，当酶浓度不变时，增加底物浓度会先增大反应速率。底物分子越多，与活性位点碰撞的机会就越大。但到某一点时，所有活性位点都被占据，称酶已饱和。反应速率达到最大值，即使继续添加更多底物也无法提高。

This behaviour can be shown on a graph. The curve of rate against substrate concentration is a rectangular hyperbola: it rises steeply initially, then levels off at a plateau.

这一行为可以用图表表示。反应速率对底物浓度的曲线是矩形双曲线：起初陡峭上升，然后趋于平缓平台。

In practical work, it is important to control enzyme concentration when investigating substrate concentration, and vice versa. Use a colorimeter to measure the intensity of colour change, or collect gas produced over time.

在实验操作中，研究底物浓度时必须控制酶浓度，反之亦然。可使用比色计测量颜色变化强度，或定时收集产生的气体。

7. Inhibitors | 抑制剂

An inhibitor is a substance that reduces the rate of an enzyme-controlled reaction. Inhibitors can be competitive or non-competitive. Competitive inhibitors have a shape similar to the substrate and compete for the active site. They block the substrate from binding, but their effect can be reduced by increasing the substrate concentration.

抑制剂是降低酶促反应速率的物质。抑制剂分为竞争性抑制剂和非竞争性抑制剂。竞争性抑制剂具有与底物相似的形状，并与底物竞争活性位点。它们阻止底物结合，但其作用可通过增加底物浓度而减弱。

Non-competitive inhibitors bind to an enzyme at a site other than the active site, called the allosteric site. This binding changes the shape of the active site, making it unable to accept the substrate. Increasing the substrate concentration does not help because the enzyme is already inactive.

非竞争性抑制剂结合在酶上除了活性位点之外的位置，称为别构位点。结合会改变活性位点的形状，使其无法接受底物。增加底物浓度无济于事，因为酶已经失活。

Many drugs and poisons work as inhibitors. For example, cyanide inhibits the enzyme cytochrome oxidase in cellular respiration, which is fatal. In medicine, some drugs inhibit specific enzymes to treat diseases, such as aspirin inhibiting the enzyme that causes inflammation.

许多药物和毒物以抑制剂的方式起作用。例如，氰化物抑制细胞呼吸中的细胞色素氧化酶，是致命的。在医学上，有些药物通过抑制特定酶来治疗疾病，如阿司匹林抑制引起炎症的酶。

8. Enzymes in Digestion | 消化中的酶

Digestion involves breaking down large insoluble food molecules into small soluble ones so they can be absorbed into the bloodstream. Each type of food requires a specific enzyme: amylase breaks down starch into maltose, protease breaks down proteins into amino acids, and lipase breaks down lipids into fatty acids and glycerol.

消化涉及将大的不溶性食物分子分解为可吸收到血液中的小分子可溶性物质。每种食物需要特定的酶：淀粉酶将淀粉分解为麦芽糖，蛋白酶将蛋白质分解为氨基酸，脂肪酶将脂质分解为脂肪酸和甘油。

These enzymes are produced in different parts of the digestive system. Salivary glands release amylase into the mouth, the stomach releases pepsin (a protease) with hydrochloric acid, and the pancreas releases digestive enzymes into the small intestine. Bile, produced by the liver, helps to emulsify fats, but it is not an enzyme.

这些酶在消化系统的不同部位产生。唾液腺在口腔中释放淀粉酶，胃释放胃蛋白酶（一种蛋白酶）和盐酸，胰腺将消化酶释放到小肠。肝脏产生的胆汁有助于乳化脂肪，但它不是酶。

The table below summarises the main digestive enzymes in humans:

下表总结了人体内主要的消化酶：

Enzyme 酶	Substrate 底物	Product 产物	Site 部位
Amylase 淀粉酶	Starch 淀粉	Maltose 麦芽糖	Mouth, pancreas, small intestine 口腔、胰腺、小肠
Protease (pepsin, trypsin) 蛋白酶（胃蛋白酶、胰蛋白酶）	Protein 蛋白质	Amino acids 氨基酸	Stomach, pancreas, small intestine 胃、胰腺、小肠
Lipase 脂肪酶	Lipids (fats) 脂质	Fatty acids + glycerol 脂肪酸+甘油	Pancreas, small intestine 胰腺、小肠

9. Industrial Applications of Enzymes | 酶的工业应用

Enzymes are widely used in industry because they are specific, work at moderate temperatures, and are environmentally friendly. In food manufacturing, amylase is used to convert starch into sugars for syrups and beverages. In the brewing industry, enzymes break down starch to produce alcohol.

酶在工业中被广泛使用，因为它们具有专一性、在温和温度下工作，并且对环境友好。在食品制造中，淀粉酶用于将淀粉转化为糖浆和饮料所需的糖。在酿造工业中，酶将淀粉分解以生产酒精。

Proteases are used in washing powders to remove protein stains such as blood and grass. They are also used in the production of leather and in the dairy industry to make cheese. Lipases are used in detergent formulations to break down fat stains and in the production of biodiesel.

蛋白酶用于洗衣粉中以去除血液和草渍等蛋白质污渍。它们也用于皮革生产和乳制品行业制造奶酪。脂肪酶用于洗涤剂配方分解油污，并用于生产生物柴油。

The table below shows some common industrial enzymes and their uses:

下表展示了一些常见工业酶及其用途：

Enzyme 酶	Use 用途
Amylase 淀粉酶	Production of glucose syrup, beer brewing 生产葡萄糖浆、啤酒酿造
Protease 蛋白酶	Biological detergents, tenderising meat 生物洗涤剂、嫩化肉类
Lipase 脂肪酶	Digestion of fat stains in detergents, cheese making 洗涤剂中分解油渍、奶酪制作
Isomerase 异构酶	Conversion of glucose to fructose for sweeteners 将葡萄糖转化为果糖用于甜味剂

10. Enzyme Immobilisation | 酶的固定化

Immobilised enzymes are enzymes that are attached to a solid support or trapped in a gel. They are used in industrial processes because they can be easily separated from the product and reused. This reduces the cost of production.

固定化酶是附着在固体载体上或包埋在凝胶中的酶。它们在工业过程中被使用，因为它们可以容易地与产物分离并被重复使用。这降低了生产成本。

One example is the use of immobilised lactase to break down lactose in milk, producing lactose-free milk for people who are lactose intolerant. The enzyme is trapped in alginate beads and the milk is passed over the beads. The lactase remains active, and the glucose and galactose produced are carried away in the milk.

一个例子是使用固定化乳糖酶分解牛奶中的乳糖，为乳糖不耐受人群生产无乳糖牛奶。乳糖酶被包埋在海藻酸盐珠中，牛奶流过珠子。乳糖酶保持活性，产生的葡萄糖和半乳糖随牛奶流走。

Advantages of immobilisation:

固定化的优点：

The enzyme can be reused many times.
酶可以多次重复使用。
The product is not contaminated by the enzyme.
产物不会被酶污染。
Enzymes are often more stable when immobilised.
固定化后酶通常更稳定。
The process can be continuous rather than batch.
该过程可以连续进行而不是分批进行。

11. Enzymes and Respiration | 酶与呼吸作用

Enzymes also control the many stages of respiration. In aerobic respiration, glucose is broken down in the presence of oxygen to release energy, carbon dioxide, and water. This process involves a series of enzyme-controlled reactions, such as glycolysis, the Krebs cycle, and the electron transport chain.

酶还控制呼吸作用的许多阶段。在有氧呼吸中，葡萄糖在氧气存在下被分解，释放能量、二氧化碳和水。这一过程涉及一系列酶促反应，如糖酵解、三羧酸循环和电子传递链。

Without enzymes, these reactions would occur too slowly to supply the energy needed for life. Each enzyme works at an optimal temperature and pH, which is why enzyme function is closely linked to cellular conditions. For example, if the temperature gets too high, denaturation stops respiration, which can be fatal.

没有酶，这些反应将进行得太慢，无法提供生命所需的能量。每种酶在最适温度和pH下工作，这就是酶功能与细胞环境紧密相连的原因。例如，如果温度过高，变性会使呼吸停止，这可能是致命的。

Enzymes also lower the activation energy of reactions. Activation energy is the minimum amount of energy required for a reaction to start. By lowering this barrier, enzymes allow reactions to occur at body temperature.

酶还降低反应的活化能。活化能是反应启动所需的最小能量。通过降低该障碍，酶使反应能够在体温条件下发生。

12. Revision Summary | 复习总结

For your IGCSE exam, remember the following key points about enzymes:

为了IGCSE考试，请记住以下关于酶的要点：

Enzymes are biological catalysts made of protein.
酶是蛋白质构成的生物催化剂。
They are specific because the active site is complementary to the substrate.
它们具有专一性，因为活性位点与底物互补。
Temperature and pH affect enzyme activity; extremes cause denaturation.
温度和pH影响酶活性；极端条件会导致变性。
Enzyme and substrate concentration affect the rate, but plateau when saturated.
酶浓度和底物浓度影响速率，但当达到饱和时会趋于平台。
Inhibitors can reduce or stop enzyme activity.
抑制剂可以降低或阻止酶活性。
Enzymes are used in digestion and industry due to their specificity and efficiency.
酶由于专一性和高效性被用于消化和工业。

Be sure to practise drawing and interpreting graphs of enzyme activity against temperature and pH. Label the optimum point and the region of denaturation. Also, remember the names of the main digestive enzymes and their substrates.

务必练习绘制和解释酶活性对温度和pH的曲线图。标注最适点和变性区域。同时，记住主要消化酶及其底物的名称。

Finally, think about how understanding enzymes helps in medicine, biotechnology, and everyday life. Enzymes are not just exam topics — they are the microscopic machines that make life possible.

最后，思考理解酶如何帮助医学、生物技术和日常生活。酶不仅仅是考试主题——它们是使生命成为可能的微观机器。

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Enzymes: Catalysts of Life | 酶：生命催化剂