Enzymes: The Biological Catalysts | 酶：生物催化剂

📚 Enzymes: The Biological Catalysts | 酶：生物催化剂

Enzymes are essential proteins that speed up chemical reactions in living organisms without being consumed in the process. They are highly specific, efficient, and sensitive to environmental conditions, making them fundamental to all aspects of life. This article explores the structure, function, and applications of enzymes, with a focus on the Edexcel IGCSE Science specification.

酶是生命体内加速化学反应的一类重要蛋白质，它们在反应过程中自身不会被消耗。酶具有高度的专一性、高效性，并对环境条件非常敏感，因此成为生命活动各个方面的基础。本文将围绕 Edexcel IGCSE 科学大纲，深入探讨酶的结构、功能及其应用。

1. What Are Enzymes? | 什么是酶？

Enzymes are biological catalysts. A catalyst is a substance that increases the rate of a chemical reaction but remains unchanged at the end. Most enzymes are globular proteins, folded into a unique three-dimensional shape that is crucial for their function.

酶是生物催化剂。催化剂是一种能提高化学反应速率，但在反应结束后自身保持不变的物质。大多数酶是球状蛋白质，折叠成独特的三维形状，这对它们的功能至关重要。

Enzymes are found in all living cells and control processes such as respiration, digestion, and photosynthesis.
They work by lowering the activation energy required for a reaction, allowing molecules to react more easily.
Each enzyme has an active site – a specific region where substrate molecules bind.

酶存在于所有活细胞中，控制着呼吸作用、消化作用和光合作用等过程。
它们通过降低反应所需的活化能来使分子更容易发生反应。
每种酶都有一个活性位点——即底物分子特异性结合的区域。

2. The Lock and Key Hypothesis | 锁与钥模型

The relationship between an enzyme and its substrate is often compared to a lock and key. The enzyme is the lock, and the substrate is the key. Only the correct substrate can fit perfectly into the enzyme’s active site, just as only the right key can turn a lock.

酶与其底物之间的关系常被比作锁和钥匙。酶是锁，底物是钥匙。只有正确形状的底物才能完美地嵌入酶的活性位点，就像只有正确的钥匙才能转动锁一样。

During the reaction, the enzyme and substrate form an enzyme-substrate complex. The reacting bonds are stressed and broken, producing products. The enzyme is then released unchanged and can catalyse more reactions.

在反应过程中，酶与底物结合形成“酶-底物复合物”。反应键受到张力作用而断裂，生成产物。随后酶被释放且保持不变，并可以继续催化更多反应。

3. The Induced Fit Model | 诱导契合模型

Modern evidence shows that the lock and key model is oversimplified. In the induced fit model, the active site is not a rigid shape. When the substrate binds, the active site changes shape slightly to fit the substrate more closely, like a glove moulding around a hand.

现代证据表明“锁与钥模型”过于简化。在“诱导契合模型”中，活性位点并非固定形状。当底物结合时，活性位点会轻微改变形状以更紧密地贴合底物，就像手套贴合手形一样。

The induced fit model explains the catalytic power of enzymes more accurately.
It also explains why some molecules that look similar to the substrate can bind but not react, acting as inhibitors.

诱导契合模型更准确地解释了酶的催化能力。
它也解释了为什么一些与底物形状相似的分子可以结合但不发生反应，从而充当抑制剂。

4. Effect of Temperature | 温度的影响

Temperature has a significant effect on enzyme activity. As temperature increases, the rate of an enzyme-catalysed reaction increases because molecules move faster and collide more frequently with the active site. For most human enzymes, the optimal temperature is about 37 °C.

温度对酶活性有显著影响。随着温度升高，酶促反应速率加快，因为分子运动速度加快，与活性位点的碰撞频率增加。对于大多数人体酶来说，最适温度约为 37 °C。

However, above the optimum temperature, the enzyme begins to denature. The heat breaks the weak bonds (hydrogen bonds and ionic bonds) that maintain the enzyme’s three-dimensional structure. The active site changes shape permanently, and the enzyme can no longer bind its substrate.

然而，超过最适温度后，酶开始变性。热量破坏了维持酶三维结构的弱键（氢键和离子键）。活性位点永久改变形状，酶无法再与底物结合。

Reaction rate increases up to optimum temperature, then decreases sharply after denaturation.

反应速率在最适温度前上升，变性后急剧下降。

5. Effect of pH | pH 的影响

Each enzyme has an optimum pH at which its activity is highest. Changes in pH alter the concentration of hydrogen ions (H⁺) and hydroxide ions (OH⁻) in the solution. These ions can disrupt hydrogen bonds and ionic bonds that keep the enzyme’s shape stable.

每种酶都有一个使其活性最高的最适 pH。pH 的变化会改变溶液中氢离子（H⁺）和氢氧根离子（OH⁻）的浓度。这些离子会破坏维持酶形状稳定的氢键和离子键。

For example, pepsin, an enzyme in the stomach, works best at pH 2 (highly acidic). Trypsin, an enzyme in the small intestine, works best at pH 8 (alkaline). If the pH deviates significantly from the optimum, the enzyme can denature.

例如，胃蛋白酶在胃中工作的最适 pH 为 2（强酸性）。胰蛋白酶在小肠中的最适 pH 为 8（碱性）。如果 pH 明显偏离最适值，酶就可能变性。

Enzyme	Optimum pH	Location
Pepsin	2	Stomach
Trypsin	8	Small intestine
Catalase	7 (neutral)	Most cells

上表列出了几种常见酶及其最适 pH 和所在位置。

6. Enzyme and Substrate Concentration | 酶浓度和底物浓度

Enzyme activity also depends on the availability of enzyme and substrate molecules. When substrate concentration increases while the enzyme concentration stays fixed, the rate of reaction increases until a maximum is reached. At this point, all active sites are occupied, and further increases in substrate concentration cannot speed up the reaction.

酶活性还取决于酶分子和底物分子的可用性。当底物浓度增加而酶浓度不变时，反应速率会上升直至达到最大值。此时所有活性位点已被占据，继续增加底物浓度也无法加快反应。

Similarly, increasing enzyme concentration, with a fixed substrate concentration, will increase the rate until the substrate becomes the limiting factor. The rate is always limited by the factor that is in shortest supply.

类似地，在底物浓度固定时增加酶浓度，反应速率会上升，直到底物成为限制因素。反应速率总是受最短缺的因素限制。

Rate ∝ [substrate] until saturation, then rate ∝ [enzyme].

速率与底物浓度成正比直到饱和，之后速率与酶浓度成正比。

7. Enzymes in Digestion | 消化中的酶

Digestion is the process of breaking down large, insoluble food molecules into smaller, soluble ones that can be absorbed. Various digestive enzymes are secreted at different points along the alimentary canal.

消化是分解大的、不溶性的食物分子为小的、可溶性分子的过程，以便它们被吸收。不同的消化酶在消化道不同位置分泌。

Amylase – starch → maltose; produced in the salivary glands and pancreas.
Protease (e.g., pepsin) – protein → amino acids; produced in the stomach and pancreas.
Lipase – fats → fatty acids and glycerol; produced in the pancreas.

淀粉酶 – 淀粉 → 麦芽糖；在唾液腺和胰腺中产生。
蛋白酶（如胃蛋白酶） – 蛋白质 → 氨基酸；在胃和胰腺中产生。
脂肪酶 – 脂肪 → 脂肪酸和甘油；在胰腺中产生。

Bile, produced by the liver and stored in the gallbladder, is not an enzyme. It emulsifies fats, increasing their surface area so lipase can work more effectively. Bile also neutralises stomach acid in the small intestine to create an optimum pH for intestinal enzymes.

胆汁由肝脏产生，储存在胆囊中，它不是酶。胆汁将脂肪乳化，增加其表面积，使脂肪酶能更有效地工作。胆汁还能中和进入小肠的胃酸，为肠道酶创造最适 pH。

8. Industrial and Medical Applications | 工业与医疗应用

Enzymes are widely used in industry and medicine because they are specific, work at moderate temperatures and pressures, and are biodegradable. This reduces energy costs and environmental pollution compared to traditional chemical processes.

酶在工业和医疗中被广泛应用，因为它们具有专一性、能在温和的温度和压力下工作且可生物降解。与传统化学工艺相比，这降低了能源成本和环境污染。

Biological detergents – contain proteases and lipases to remove protein and fat stains.
Food industry – glucose isomerase converts glucose to fructose (sweeter); pectinase clarifies fruit juices.
Medical diagnostics – glucose oxidase strips measure blood glucose levels in diabetics.
Biotechnology – restriction enzymes cut DNA at specific sequences for genetic engineering.

生物洗涤剂 – 含有蛋白酶和脂肪酶以去除蛋白质和脂肪污渍。
食品工业 – 葡萄糖异构酶将葡萄糖转化为果糖（更甜）；果胶酶用于澄清果汁。
医疗诊断 – 葡萄糖氧化酶试纸用于测量糖尿病患者的血糖水平。
生物技术 – 限制性内切酶在特定序列处切割 DNA，用于基因工程。

9. Enzyme Inhibition | 酶抑制

Some substances can reduce enzyme activity. These are called inhibitors. Competitive inhibitors have a similar shape to the substrate and compete for the active site. If the inhibitor is present in high concentration, it blocks more active sites and lowers the reaction rate. This can be reversed by adding more substrate.

有些物质能降低酶活性，称为抑制剂。竞争性抑制剂与底物形状相似，与底物竞争活性位点。如果抑制剂浓度较高，它会占据更多活性位点并降低反应速率。增加底物浓度可以逆转这种抑制。

Non-competitive inhibitors bind to a different site on the enzyme (the allosteric site). This changes the shape of the active site, making it unable to bind the substrate. Adding more substrate does not overcome non-competitive inhibition because the enzyme is permanently altered.

非竞争性抑制剂结合在酶的不同位点（别构位点）上。这会改变活性位点的形状，使其无法结合底物。增加底物浓度不能克服非竞争性抑制，因为酶已被永久改变。

Competitive inhibition: inhibitor competes for the active site; Non-competitive: inhibitor binds elsewhere and alters the active site.

竞争性抑制：抑制剂竞争活性位点；非竞争性抑制：抑制剂结合别处并改变活性位点。

10. Summary and Exam Tips | 总结与备考提示

Enzymes are fundamental to IGCSE Biology. To score high marks, you should be able to describe enzyme structure, explain the lock-and-key and induced-fit models, and interpret graphs of temperature and pH effects. Pay attention to the word “denature” – it means permanent change in protein structure, not simply “destroyed”.

酶是IGCSE生物学的基础。要取得高分，你需要能够描述酶的结构，解释“锁钥模型”和“诱导契合模型”，并解读温度和pH影响的曲线图。注意“变性”一词——它指的是蛋白质结构发生永久性改变，而不是简单的“被破坏”。

Always define the active site when explaining enzyme specificity.
Remember that catalysts lower activation energy and are unchanged after a reaction.
Do not confuse inhibitors with denaturation: inhibitors do not necessarily destroy the enzyme; denaturation does.

在解释酶专一性时，务必定义活性位点。
记住催化剂降低活化能且反应后自身不变。
不要把抑制剂与变性混淆：抑制剂不一定破坏酶，而变性是破坏。

Practising graph-based questions, such as plotting the effect of temperature on reaction rate and identifying the optimum temperature, is essential for exam success.

练习基于图形的问题，例如绘制温度对反应速率的影响并识别最适温度，对考试成功至关重要。

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Enzymes: The Biological Catalysts | 酶：生物催化剂