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

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

In IGCSE Biology, enzymes are one of the most important topics because they explain how reactions inside living cells are controlled. This article covers the key concepts, definitions, graphs and practical applications that you need for your Edexcel exam.

在IGCSE生物中，酶是最重要的主题之一，因为它解释了活细胞内的反应是如何被调控的。这篇文章涵盖了你在爱德思考试中需要掌握的核心概念、定义、图像和实际应用。

1. What Are Enzymes? | 什么是酶？

Enzymes are biological catalysts that speed up chemical reactions without being used up or permanently changed in the process. They are made of protein and have a specific three-dimensional shape.

酶是生物催化剂，能够在不被消耗或永久改变的情况下加速化学反应。它们由蛋白质构成，具有特定的三维形状。

Almost all metabolic reactions in cells rely on enzymes. Without enzymes, reactions such as respiration and photosynthesis would be far too slow to support life.

细胞中几乎所有的代谢反应都依赖酶。没有酶，呼吸作用和光合作用等反应会慢到无法维持生命。

2. The Active Site | 活性位点

Each enzyme has a region called the active site. The active site has a specific shape that only allows certain substrate molecules to bind to it. This is called the lock and key model.

每种酶都有一个称为活性位点的区域。活性位点具有特定形状，只允许特定的底物分子与其结合。这称为锁钥模型。

In the lock and key model, the enzyme is the lock and the substrate is the key. When the substrate fits into the active site, an enzyme-substrate complex is formed, and the reaction then takes place.

在锁钥模型中，酶是锁，底物是钥匙。当底物与活性位点匹配时，会形成酶-底物复合物，随后反应发生。

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

酶 + 底物 → 酶-底物复合物 → 酶 + 产物

3. Enzyme Specificity | 酶的专一性

Enzymes are specific because the active site has a unique shape that only one type of substrate can exactly fit. This explains why enzymes that break down starch cannot break down protein or fat.

酶具有专一性，因为活性位点具有独特的形状，只有一种底物能够精确匹配。这就解释了为什么分解淀粉的酶不能分解蛋白质或脂肪。

Examples include amylase, which breaks down starch into maltose, and protease, which breaks down proteins into amino acids. Each enzyme works on a particular substrate only.

例如，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。每种酶只作用于特定底物。

4. Enzyme-Controlled Reactions in Daily Life | 酶在日常生活中的作用

Enzymes are used in many biological processes. In digestion, amylase is produced in the salivary glands and pancreas. Protease is produced in the stomach and pancreas, while lipase is produced in the pancreas and breaks down fats into fatty acids and glycerol.

酶在众多生物过程中发挥作用。在消化中，唾液腺和胰腺分泌淀粉酶。胃和胰腺分泌蛋白酶，而胰腺分泌脂肪酶，将脂肪分解为脂肪酸和甘油。

Enzymes are also used in industry, for example in biological washing powders where lipase and protease remove fat and protein stains. They work at low temperatures, which saves energy.

酶也用于工业，例如在生物洗衣粉中，脂肪酶和蛋白酶去除油渍和蛋白污渍。它们在低温下工作，从而节省能源。

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

Temperature affects the rate of enzyme-controlled reactions. As temperature increases, particles move faster and collide more often, so the rate of reaction increases. However, this only happens up to a certain point.

温度影响酶促反应的速率。随着温度升高，颗粒运动加快，碰撞更频繁，因此反应速率加快。然而，这只是在一定范围内如此。

The optimum temperature for most human enzymes is around 37 °C. Above this temperature, the rate increases briefly, but then the enzyme begins to denature.

大多数人体酶的最适温度约为37 °C。超过这一温度后，反应速率会短暂上升，但随后酶开始变性。

Denaturation is a permanent change in the shape of the active site. The substrate can no longer fit, so the reaction stops. In most enzymes, denaturation begins around 40-45 °C and is irreversible.

变性是活性位点形状的永久改变。底物无法再与之结合，反应停止。大多数酶在约40-45 °C开始变性，且不可逆。

Denaturation: 3D shape of active site changes permanently → reaction stops

变性：活性位点的三维形状永久改变 → 反应停止

6. The Temperature Graph | 温度曲线图

When plotting rate of reaction against temperature, the curve rises to a peak at the optimum temperature, then falls sharply to zero after denaturation. The shape is roughly a curve that increases then decreases.

当绘制反应速率对温度的曲线时，曲线在最适温度处达到峰值，然后在变性后急剧下降至零。曲线形状大致先升后降。

Remember to label the optimum temperature as the highest point on the graph. For human enzymes, this is about 37 °C, but for enzymes from bacteria that live in hot springs, the optimum can be much higher.

记住将曲线最高点标记为最适温度。人体酶的最适温度约为37 °C，但对于生活在热泉中的细菌酶，最适温度要高得多。

Low temperature: slow movement, fewer collisions, low rate.
低温：运动慢，碰撞少，速率低。
Optimum temperature: highest rate of reaction.
最适温度：反应速率最高。
High temperature: enzyme denatures, rate drops to zero.
高温：酶变性，速率降至零。

7. pH and Enzyme Activity | pH与酶活性

Each enzyme has an optimum pH. Most enzymes work best in neutral conditions around pH 7, but some have different optima. For example, pepsin in the stomach works best at pH 2.

每种酶都有最适pH。大多数酶在中性条件（pH 7左右）下活性最高，但有些酶有不同的最适pH。例如，胃中的胃蛋白酶在pH 2时活性最高。

Extreme pH values can denature enzymes. High levels of hydrogen ions can break the hydrogen bonds that hold the protein structure together, changing the shape of the active site permanently.

极端pH值会使酶变性。高浓度的氢离子会破坏维持蛋白质结构的氢键，使活性位点的形状永久改变。

In the exam, you may be asked to interpret a pH graph. The curve is usually bell-shaped, with a peak at the optimum pH and lower rates on both sides.

在考试中，你可能会被要求解读pH曲线图。曲线通常呈钟形，峰值在最适pH处，两侧速率较低。

8. Substrate Concentration and Enzyme Activity | 底物浓度与酶活性

If the amount of enzyme is fixed, increasing substrate concentration will initially increase the rate of reaction. This is because more substrate means more frequent collisions with active sites.

如果酶量固定，增加底物浓度会最初增加反应速率。这是因为更多的底物意味着与活性位点碰撞更频繁。

However, after a certain point, all active sites are occupied. This is called saturation. Adding more substrate will not increase the rate any further because the enzyme is working at its maximum rate.

然而，超过一定点后，所有活性位点都被占据。这称为饱和。继续增加底物不会再提高速率，因为酶已经以最大速率工作。

The graph of rate against substrate concentration is a curve that increases steeply at first and then flattens into a horizontal plateau.

反应速率对底物浓度的曲线先急剧上升，然后趋于平坦，呈平台状。

9. Enzyme Concentration and Enzyme Activity | 酶浓度与酶活性

If substrate is in excess, increasing enzyme concentration will increase the rate of reaction linearly. More enzyme molecules mean more active sites available, so more reactions can occur per unit time.

如果底物过量，增加酶浓度会线性增加反应速率。酶分子越多，可用的活性位点越多，因此单位时间内发生的反应也越多。

If enzyme concentration is doubled, the rate of reaction roughly doubles, as long as there is enough substrate and other conditions remain constant.

酶的浓度加倍，反应速率大约加倍，前提是有足够的底物且其他条件保持不变。

When the enzyme concentration is the limiting factor, the graph is a straight line passing through the origin. There is no plateau because enzyme is always being added.

当酶浓度是限制因素时，曲线是一条通过原点的直线。不存在平台，因为酶在不断增加。

10. Inhibitors and Their Effects | 抑制剂及其作用

Inhibitors are substances that reduce the rate of an enzyme-controlled reaction. There are two main types: competitive inhibitors and non-competitive inhibitors.

抑制剂是降低酶促反应速率的物质。主要有两种类型：竞争性抑制剂和非竞争性抑制剂。

A competitive inhibitor has a shape similar to the substrate. It competes with the substrate for the active site. If it binds, the enzyme is temporarily blocked. Increasing substrate concentration can overcome this type of inhibition.

竞争性抑制剂的形状与底物相似。它与底物竞争活性位点。如果它结合了，酶被暂时阻断。增加底物浓度可以克服这种抑制。

A non-competitive inhibitor binds to another part of the enzyme, not the active site. This changes the shape of the active site, so the substrate cannot bind. Increasing substrate concentration does not help because the enzyme is permanently changed.

非竞争性抑制剂结合在酶的其他位置，而非活性位点。这会改变活性位点的形状，使底物无法结合。增加底物浓度没有帮助，因为酶已经永久改变。

Heavy metal ions such as mercury and lead are examples of non-competitive inhibitors. They can be toxic to living organisms because they stop vital enzymes from working.

重金属离子如汞和铅是非竞争性抑制剂的例子。它们对生物体有毒，因为会阻断关键酶的活性。

11. Enzymes in Biotechnology | 生物技术中的酶

Enzymes are widely used in biotechnology. For example, a microorganism can be genetically modified to produce human insulin using enzymes. In the food industry, enzymes are used to make cheese, bread and fruit juice.

酶在生物技术中广泛使用。例如，可以用酶改造微生物使其产生人胰岛素。在食品工业中，酶用于制作奶酪、面包和果汁。

In genetic engineering, enzymes called restriction enzymes cut DNA at specific sequences. DNA ligase joins DNA fragments together. These enzymes are essential tools for creating recombinant DNA.

在基因工程中，称为限制性内切酶的酶在特定序列处切割DNA。DNA连接酶将DNA片段连接在一起。这些酶是创造重组DNA的重要工具。

Enzymes are chosen for industrial use because they are specific, work at moderate temperatures, and are biodegradable, making them environmentally friendly compared to chemical catalysts.

酶被选择用于工业是因为它们具有专一性、在温和温度下工作，并且可生物降解，因此比化学催化剂更环保。

12. Experimental Design and Exam Tips | 实验设计与考试技巧

In Edexcel IGCSE Biology experiments, you may use amylase with starch and iodine solution to show how temperature affects enzyme activity. The iodine solution turns blue-black in the presence of starch. A faster disappearance of colour means a faster reaction.

在爱德思IGCSE生物实验中，你可能会用淀粉酶、淀粉和碘液来显示温度如何影响酶活性。碘液遇淀粉变蓝黑色。颜色消失越快说明反应越快。

When designing an experiment, measure the time for the starch to be fully digested. Use a water bath to control temperature and repeat each measurement to improve reliability. Keep the concentration of amylase and starch constant throughout.

设计实验时，测量淀粉完全被消化所需的时间。使用水浴控制温度，并重复每次测量以提高可靠性。在整个过程中保持淀粉酶和淀粉的浓度不变。

For a model of the lock and key theory, you can use shapes to show how only certain puzzles fit together. Remember that the active site shape is essential for specificity and any change leads to loss of function.

对于锁钥模型的演示，你可以用形状展示只有特定的拼图能组合在一起。记住，活性位点的形状对专一性至关重要，任何改变都会导致功能丧失。

Summary | 总结: Enzymes are specific biological catalysts whose activity is affected by temperature, pH, substrate concentration and inhibitors. Understanding the lock and key model and being able to interpret graphs are essential for exam success.

总结：酶是专一的生物催化剂，其活性受温度、pH、底物浓度和抑制剂影响。理解锁钥模型并能够解读曲线图对考试成功至关重要。

Published by TutorHao | Biology Revision Series | aleveler.com

更多咨询请联系16621398022（同微信）

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