Enzymes: Biological Catalysts | 酶：生物催化剂

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

Enzymes are remarkable proteins that accelerate chemical reactions in living organisms. They are essential for life, controlling processes from digestion to DNA replication. In this revision guide, you will explore how enzymes work, what affects their activity, and why they are so important in both biology and industry.

酶是能够加速生物体内化学反应的非凡蛋白质。它们是生命所必需的，控制着从消化到DNA复制等过程。在本复习指南中，你将探索酶如何工作、哪些因素影响其活性，以及为什么它们在生物学和工业中如此重要。

1. What Are Enzymes? | 什么是酶？

Enzymes are biological catalysts made of proteins. They increase the rate of a chemical reaction by lowering the activation energy needed for the reaction to occur.

酶是由蛋白质构成的生物催化剂。它们通过降低反应所需的活化能来提高化学反应速率。

Key facts about enzymes:

关于酶的关键事实：

Enzymes are not changed permanently by the reactions they catalyse.
酶不会因催化的反应而被永久改变。
Each enzyme is specific to one substrate or a small group of substrates.
每种酶只对一种底物或一小类底物具有特异性。
Enzyme activity is controlled by temperature, pH, and concentration.
酶的活性受温度、pH值和浓度的控制。

2. The Active Site and Specificity | 活性位点与特异性

The active site is a particular region of the enzyme where the substrate binds. It has a unique three-dimensional shape, complementary to the substrate molecule.

活性位点是酶上底物结合的特殊区域。它具有独特的三维形状，与底物分子互补。

This shape is determined by the enzyme’s amino acid sequence and folding. If the active site changes shape, the enzyme can no longer work.

这种形状由酶的氨基酸序列和折叠方式决定。如果活性位点形状改变，酶就不能再起作用。

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

酶 + 底物 → 酶-底物复合物 → 酶 + 产物

3. Lock-and-Key vs. Induced Fit | 锁钥模型与诱导契合

The lock-and-key model states that the active site is a rigid shape that exactly matches the substrate, like a key fits a lock.

锁钥模型认为活性位点是刚性的形状，与底物精确匹配，就像钥匙配锁一样。

The induced fit model is more modern: the active site is flexible and changes shape slightly when the substrate binds, improving the fit and enabling catalysis.

诱导契合模型更为现代：活性位点具有柔性，当底物结合时形状略有改变，以改善匹配并实现催化。

Model	Description	模型	描述
Lock-and-key	Active site is rigid and pre-shaped.	锁钥	活性位点刚硬且预成型。
Induced fit	Active site moulds around the substrate.	诱导契合	活性位点围绕底物成型。

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

Several factors alter how quickly an enzyme works. These include temperature, pH, substrate concentration, enzyme concentration, and the presence of inhibitors.

多个因素会改变酶工作的速率。这些包括温度、pH、底物浓度、酶浓度以及抑制剂的存在。

Studying these factors helps scientists control enzyme reactions in industry and medicine.

研究这些因素有助于科学家在工业和医学中控制酶反应。

Temperature affects molecular movement and enzyme structure.
温度影响分子运动和酶的结构。
pH changes the charges on active site amino acids.
pH改变活性位点氨基酸上的电荷。
Higher substrate concentration increases rate until saturation.
较高的底物浓度会提高速率直至饱和。

5. Effect of Temperature | 温度的影响

As temperature rises, molecules move faster and collide more often, so the rate of enzyme-catalysed reaction increases.

随着温度升高，分子运动加快，碰撞更频繁，因此酶催化反应的速率增加。

However, above an optimum temperature, the enzyme’s structure begins to break down. This is called denaturation.

然而，超过最适温度后，酶的结构开始瓦解。这称为变性。

The optimum temperature for most human enzymes is about 37°C.

大多数人体酶的最适温度约为37°C。

6. Effect of pH | pH的影响

Every enzyme has an optimum pH at which it works fastest. For example, pepsin in the stomach works best at pH 2, while pancreatic enzymes work best at pH 8.

每种酶都有其工作最快的最适pH。例如，胃中的胃蛋白酶在pH 2时作用最佳，而胰酶在pH 8时作用最佳。

Extreme pH values can denature the enzyme by disrupting ionic bonds and hydrogen bonds in its structure.

极端的pH值通过破坏酶结构中的离子键和氢键而使酶变性。

Below optimum pH → Rate decreases; Above optimum pH → Rate decreases

低于最适pH → 速率下降；高于最适pH → 速率下降

7. Effect of Substrate and Enzyme Concentration | 底物与酶浓度的影响

When enzyme concentration is increased, the rate of reaction increases because there are more active sites available.

当酶浓度增加时，反应速率增加，因为有更多的活性位点可用。

When substrate concentration is increased, the rate also increases, but only up to a point. Once all active sites are occupied, adding more substrate has no further effect.

当底物浓度增加时，速率也会增加，但只到一定程度。一旦所有活性位点都被占据，再添加底物也不会产生进一步影响。

If enzyme concentration doubles, rate roughly doubles (with excess substrate).
如果酶浓度加倍（底物过量），速率大约加倍。
At high substrate concentration, the reaction reaches Vmax.
在高底物浓度下，反应达到最大速率。

8. Inhibitors | 抑制剂

Inhibitors are substances that reduce the activity of an enzyme. Competitive inhibitors compete with the substrate for the active site.

抑制剂是降低酶活性的物质。竞争性抑制剂与底物竞争活性位点。

Non-competitive inhibitors bind elsewhere on the enzyme, changing its shape so that the active site no longer works.

非竞争性抑制剂结合在酶的其他部位，改变其形状，使活性位点不再工作。

In medicine, inhibitors are used to control harmful enzymes in bacteria or cancer cells.

在医学中，抑制剂被用来控制细菌或癌细胞中的有害酶。

9. Enzymes in Digestion | 消化中的酶

Digestive enzymes break large food molecules into smaller, soluble molecules that can be absorbed.

消化酶将大的食物分子分解成可吸收的小的可溶性分子。

Enzyme	Substrate	Product	酶	底物	产物
Amylase	Starch	Maltose	淀粉酶	淀粉	麦芽糖
Protease	Protein	Amino acids	蛋白酶	蛋白质	氨基酸
Lipase	Lipids	Fatty acids + glycerol	脂肪酶	脂类	脂肪酸 + 甘油

10. Industrial Uses of Enzymes | 酶的工业应用

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

酶在工业中被广泛使用，因为它们具有特异性、在温和温度下工作，并且可生物降解。

Biological washing powders use proteases and lipases to remove stains.
生物洗衣粉使用蛋白酶和脂肪酶去除污渍。
Glucose syrup is made from starch using amylase and glucoamylase.
葡萄糖浆是用淀粉酶和葡萄糖淀粉酶从淀粉中制成的。
Lactase is used to produce lactose-free milk.
乳糖酶用于生产无乳糖牛奶。

11. Enzyme Technology in Everyday Life | 酶在日常生活中的应用

Enzymes also appear in food processing, brewing, and medical diagnostics.

酶也出现在食品加工、酿造和医学诊断中。

For example, catalase is used to remove hydrogen peroxide in food packaging, and restriction enzymes are used in genetic engineering to cut DNA at specific sequences.

例如，过氧化氢酶用于去除食品包装中的过氧化氢，限制性内切酶用于基因工程中在特定序列处切割DNA。

Understanding enzymes allows scientists to design better drugs and sustainable industrial processes.

理解酶使科学家能够设计更好的药物和可持续的工业过程。

12. Summary and Exam Tips | 总结与考试提示

In IGCSE Science exams, you must be able to interpret graphs of enzyme activity, explain denaturation, and state the effect of inhibitors.

在IGCSE科学考试中，你必须能够解读酶活性曲线图、解释变性，并说明抑制剂的影响。

Remember the key vocabulary: substrate, active site, product, denaturation, optimum, competitive inhibitor.

记住关键词汇：底物、活性位点、产物、变性、最适、竞争性抑制剂。

Rate of reaction ∝ 1 / time taken

反应速率 ∝ 1 / 所需时间

Always use ‘denatured’ instead of ‘killed’ for enzymes, because enzymes are not alive.

对于酶，始终使用’变性’而不是’杀死’，因为酶不是活的。

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Enzymes: Biological Catalysts | 酶：生物催化剂