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

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

Enzymes are biological molecules that speed up chemical reactions in living organisms without being used up themselves. They are essential for processes such as digestion, respiration and photosynthesis. In this article, you will learn about the structure, function and applications of enzymes, with a special focus on the Edexcel IGCSE Science specification.

酶是生物分子，能够在不被消耗的前提下加快生物体内的化学反应。它们在消化、呼吸和光合作用等过程中至关重要。在本文中，你将了解酶的结构、功能和应用，并重点关注 Edexcel IGCSE 科学考纲中的内容。

1. What Are Enzymes? | 什么是酶？

Enzymes are proteins made up of long chains of amino acids. Each enzyme has a specific three-dimensional shape, which is determined by the sequence of amino acids. The shape includes a special region called the active site, where the substrate binds.

酶是由氨基酸长链构成的蛋白质。每种酶都有特定的三维形状，该形状由氨基酸序列决定。这个形状包含一个称为活性位点的特殊区域，底物在此处结合。

An enzyme is specific to one substrate because the active site has a complementary shape. This is often described as a ‘lock and key’ mechanism.

酶对底物具有专一性，因为活性位点具有互补形状。这通常被描述为 ‘锁钥’ 机制。

Enzymes are not changed permanently by the reactions they catalyse.

酶不会因催化反应而发生永久性改变。
Enzymes work at optimal temperatures and pH values in living cells.

酶在活细胞中于最适温度和 pH 值下发挥作用。

2. The Lock and Key Hypothesis | 锁钥模型

The lock and key hypothesis explains enzyme specificity. The enzyme is the ‘lock’, and the substrate is the ‘key’. Only the correct key fits into the lock, forming an enzyme-substrate complex.

锁钥模型解释了酶的专一性。酶是 ‘锁’，底物是 ‘钥匙’。只有正确的钥匙才能插入锁孔，形成酶-底物复合物。

When the substrate binds to the active site, the reaction occurs quickly. The products then leave the active site, allowing the enzyme to catalyse another reaction.

当底物与活性位点结合时，反应快速发生。产物随后离开活性位点，使酶能够催化下一个反应。

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

酶 + 底物 → 酶-底物复合物 → 酶 + 产物

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

Several factors can change the rate of an enzyme-controlled reaction. These include temperature, pH, enzyme concentration, substrate concentration and inhibitors.

多种因素可以改变酶促反应速率，包括温度、pH、酶浓度、底物浓度和抑制剂。

Factor	Effect
Temperature	Increases rate up to optimum, then decreases.
pH	Each enzyme has an optimal pH; extreme pH denatures it.
Enzyme concentration	Higher enzyme concentration increases rate until substrate runs out.
Substrate concentration	Higher substrate concentration increases rate until all active sites are occupied.
Inhibitors	Slow down or stop enzyme activity.

表格

For an IGCSE exam, you should be able to interpret graphs of enzyme activity against these variables.

在 IGCSE 考试中，你应能解读酶活性随这些变量变化的曲线图。

4. Temperature and pH | 温度和 pH

As temperature increases, molecules move faster and collide more often. This increases the rate of reaction up to a point called the optimum temperature. For most human enzymes, the optimum is around 37 °C.

随着温度升高，分子运动加快，碰撞频率增加。在某个称为最适温度的点之前，反应速率随之升高。大多数人体酶的最适温度约为 37 °C。

Above the optimum temperature, the enzyme’s three-dimensional structure begins to break down. This is called denaturation. The active site changes shape, so the substrate can no longer bind.

超过最适温度后，酶的三维结构开始被破坏，这称为变性。活性位点的形状改变，底物无法再与其结合。

Similarly, each enzyme works best at a specific pH. For example, pepsin works at pH 2 in the stomach, while amylase works best at pH 7 in the mouth and small intestine.

同样，每种酶都有其最适 pH。例如，胃蛋白酶在胃中的 pH 2 条件下工作，而唾液淀粉酶在口腔和小肠中的 pH 7 条件下工作最佳。

In extreme pH conditions, ionic bonds and hydrogen bonds in the protein are disrupted, leading to denaturation.

在极端 pH 条件下，蛋白质中的离子键和氢键被破坏，导致变性。

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

When enzyme concentration increases, there are more active sites available. The rate of reaction increases linearly, assuming substrate is in excess. However, if substrate is limited, adding more enzyme will have no further effect.

当酶浓度增加时，可用的活性位点增多。在底物过量的情况下，反应速率呈线性增加。然而，如果底物有限，添加更多酶将不会产生进一步影响。

When substrate concentration increases, the rate of reaction increases because collisions with active sites become more frequent. Eventually, all active sites are occupied at any given moment, and the reaction reaches its maximum velocity (Vmax).

当底物浓度增加时，由于与活性位点的碰撞更频繁，反应速率增加。最终，所有活性位点在任意时刻均被占据，反应达到最大速率（Vmax）。

Rate ∝ Enzyme concentration (when substrate is in excess)

速率 ∝ 酶浓度（当底物过量时）

6. Inhibitors | 抑制剂

An inhibitor is a substance that reduces the rate of an enzyme-catalysed reaction. Inhibitors can be competitive or non-competitive.

抑制剂是降低酶促反应速率的物质。抑制剂可分为竞争性抑制剂和非竞争性抑制剂。

A competitive inhibitor has a similar shape to the substrate and competes for the active site. If it binds, it blocks the substrate from entering. This inhibition can be overcome by increasing the substrate concentration.

竞争性抑制剂的形状与底物相似，会竞争活性位点。如果它结合上去，就会阻止底物进入。这种抑制可以通过增加底物浓度来克服。

A non-competitive inhibitor binds to a site other than the active site. This changes the shape of the enzyme, so the active site no longer works. Adding more substrate does not help.

非竞争性抑制剂结合在活性位点以外的位置，这会改变酶的形状，使活性位点无法正常工作。增加底物浓度也无法解决。

In IGCSE Biology, you also learn about the use of inhibitors in controlling metabolic pathways.

在 IGCSE 生物中，你还会学习抑制剂在控制代谢途径中的应用。

7. Enzymes in Digestion | 消化中的酶

Digestion is the process of breaking down large insoluble food molecules into small soluble molecules that can be absorbed into the blood.

消化是将大的不溶性食物分子分解为可被血液吸收的小的可溶性分子的过程。

Amylase breaks down starch into maltose in the mouth and small intestine.

唾液淀粉酶和小肠中的淀粉酶将淀粉分解为麦芽糖。
Proteases, such as pepsin and trypsin, break down proteins into amino acids.

蛋白酶，如胃蛋白酶和胰蛋白酶，将蛋白质分解为氨基酸。
Lipases break down fats into fatty acids and glycerol.

脂肪酶将脂肪分解为脂肪酸和甘油。

Bile, produced by the liver and stored in the gallbladder, is not an enzyme. It emulsifies fat into small droplets to increase the surface area for lipase to work.

胆汁由肝脏产生并储存于胆囊内，它不是酶。胆汁将脂肪乳化成小液滴，从而增大表面积，便于脂肪酶作用。

8. Enzymes in Industry | 工业中的酶

Enzymes are widely used in industry because they are specific, work at moderate temperatures and are biodegradable.

酶在工业中广泛应用，因为它们具有专一性、在温和温度下工作且可生物降解。

Biological washing powders contain proteases and lipases to remove protein and fat stains. These enzymes work best at low temperatures, saving energy.

生物洗衣粉含有蛋白酶和脂肪酶，用于去除蛋白质和脂肪污渍。这些酶在低温下效果最佳，从而节省能源。

Fructose syrup is produced from glucose using the enzyme glucose isomerase. Glucose syrup is cheaper, but a mixture of glucose and fructose is sweeter.

果葡糖浆利用葡萄糖异构酶从葡萄糖制备。葡萄糖浆较便宜，但葡萄糖和果糖的混合物更甜。

Enzymes are also used in the food industry to produce cheese, bread and beer.

酶也被用于食品工业，以生产奶酪、面包和啤酒。

9. Uses of Immobilised Enzymes | 固定化酶的应用

Immobilised enzymes are enzymes attached to an inert support, such as alginate beads or silica gel. They are used in industrial processes because they can be reused easily and the products are not contaminated with the enzyme.

固定化酶是附着在惰性载体（如海藻酸盐珠或硅胶）上的酶。它们用于工业生产过程，因为易于重复使用，且产物不会被酶污染。

A common example is the production of fructose syrup. Glucose is passed through a column containing immobilised glucose isomerase. The enzyme converts glucose to fructose continuously.

一个常见例子是果葡糖浆的生产。葡萄糖通过含有固定化葡萄糖异构酶的柱，酶持续将葡萄糖转化为果糖。

Immobilised enzymes also help in the production of semi-synthetic antibiotics. For example, penicillin acylase is used to modify penicillin to form amoxicillin.

固定化酶还用于半合成抗生素的生产。例如，青霉素酰化酶被用于修饰青霉素以形成阿莫西林。

Advantages of immobilisation:

固定化的优点：

The enzyme can be recovered and reused.

酶可以被回收和重复使用。
The product is pure and needs less purification.

产物纯净，需要较少纯化。
The enzyme is more stable and works over a wider temperature range.

酶更稳定，工作温度范围更广。

10. Conclusion | 总结

Enzymes are vital biological catalysts that control metabolism in all living organisms. Their specificity and efficiency make them essential in both biology and industry. Understanding the factors that affect enzyme activity allows scientists to control reactions in medicine, food production and biotechnology.

酶是至关重要的生物催化剂，控制着所有生物体内的新陈代谢。它们的专一性和高效性使其在生物学和工业中都不可或缺。理解影响酶活性的因素使得科学家能够在医学、食品生产和生物技术中控制反应。

Remember these key points for your Edexcel IGCSE examination:

请记住以下 Edexcel IGCSE 考试的关键点：

Enzymes are proteins with a specific active site.

酶是具有特定活性位点的蛋白质。
They are denatured by high temperatures and extreme pH.

它们会被高温和极端 pH 变性。
Enzyme and substrate concentration affect the rate of reaction.

酶浓度和底物浓度会影响反应速率。
Digestive enzymes convert insoluble foods into soluble products.

消化酶将不溶性食物转化为可溶性产物。
Immobilised enzymes are commercially useful and reusable.

固定化酶具有商业价值且可重复使用。

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