📚 Enzymes: The Catalysts of Life | 酶：生命的催化剂
Enzymes are one of the most frequently tested topics in Edexcel IGCSE Science (Biology). Examiners love to ask about the lock-and-key model, the effects of temperature and pH on enzyme activity, and real-world applications such as biological detergents. This revision guide pairs every key idea with Chinese explanations, so you can master the scientific vocabulary and the concepts behind it at the same time.
酶是 Edexcel IGCSE 科学（生物）中最高频的考点之一。考官特别喜欢考察锁钥模型、温度和 pH 对酶活性的影响，以及生物洗涤剂等实际应用。本复习指南将每个关键概念都配上中文解释，帮助你同时掌握科学词汇和背后的原理。
1. What Are Enzymes? | 什么是酶？
Enzymes are biological catalysts. A catalyst is a substance that speeds up a chemical reaction but is not used up or permanently changed by the reaction. This means one enzyme molecule can be used over and over again. Almost all enzymes are proteins, and their function depends entirely on their three-dimensional shape.
酶是生物催化剂。催化剂是一种能加速化学反应，但自身不会被反应消耗或永久改变的物质。这意味着一个酶分子可以反复使用。几乎所有的酶都是蛋白质，其功能完全取决于它们的三维形状。
Each enzyme catalyses only one reaction or one type of reaction. This property is called specificity. For example, amylase only breaks down starch; it does not break down protein or fat. You must be able to name some common enzymes and their substrates.
每种酶只催化一种反应或一类反应，这个特性称为特异性。例如，淀粉酶只分解淀粉，不会分解蛋白质或脂肪。你必须能够说出一些常见酶及其底物。
| Enzyme 酶 | Substrate 底物 | Product 产物 |
| Amylase 淀粉酶 | Starch 淀粉 | Maltose 麦芽糖 |
| Protease 蛋白酶 | Protein 蛋白质 | Amino acids 氨基酸 |
| Lipase 脂肪酶 | Lipid 脂肪 | Fatty acids + glycerol 脂肪酸 + 甘油 |
| Catalase 过氧化氢酶 | Hydrogen peroxide 过氧化氢 | Water + oxygen 水 + 氧气 |
2. The Lock and Key Hypothesis | 锁钥模型
The active site is a small region on the surface of an enzyme where the substrate binds. The shape of the active site is complementary to the shape of the substrate, which is why only a specific substrate can fit. According to the lock-and-key model, the enzyme is the lock, the substrate is the key, and only the correct key can open the lock.
活性位点是酶表面上一小块与底物结合的区域。活性位点的形状与底物的形状互补，因此只有特定的底物才能匹配。根据锁钥模型，酶是锁，底物是钥匙，只有正确的钥匙才能打开这把锁。
When the substrate enters the active site, an enzyme-substrate complex is formed. The reaction happens quickly, and the products leave the active site. The enzyme is unchanged and can immediately accept another substrate molecule. You should be able to draw and label this sequence in a diagram question.
当底物进入活性位点后，就形成了酶-底物复合物。反应迅速发生，产物离开活性位点。酶本身没有改变，可以立即接受下一个底物分子。在作图题中，你应该能够画出并标注这一过程。
Enzyme + Substrate → Enzyme-Substrate Complex → Enzyme + Products
酶 + 底物 → 酶-底物复合物 → 酶 + 产物
3. Effect of Temperature | 温度的影响
Temperature affects the rate of an enzyme-controlled reaction because it changes the kinetic energy of the molecules. At low temperatures, enzyme and substrate molecules move slowly, so they collide less frequently and the rate is low. As the temperature rises, the molecules gain energy, collide more often, and the rate of reaction increases.
温度通过改变分子的动能来影响酶促反应速率。在低温下，酶和底物分子运动缓慢，碰撞次数少，因此反应速率低。随着温度升高，分子获得更多能量，碰撞更频繁，反应速率随之升高。
The rate reaches a maximum at the optimum temperature. For enzymes in the human body, this is usually around 37 °C. After the optimum, the rate falls sharply. The heat causes vibrations inside the enzyme molecule to become so violent that the weak bonds holding the protein in its exact shape break. The active site changes shape permanently and can no longer bind the substrate. The enzyme is said to be denatured.
速率在最适温度时达到最大值。人体内酶的最适温度通常约为 37 °C。超过最适温度后，速率急剧下降。热量使酶分子内部的振动过于剧烈，维持蛋白质精确形状的弱键发生断裂。活性位点永久改变形状，无法再结合底物，这时称酶发生了变性。
Remember that denaturation is permanent — an enzyme cannot ‘recover’ once denatured. This is why washing clothes at very high temperatures destroys the enzymes in biological detergents. Also, you must never write that enzymes are ‘killed’ — enzymes are not alive.
请记住，变性是不可逆的——酶一旦变性就无法“恢复”。这就是为什么用极高温的水洗衣服会破坏生物洗涤剂中的酶。另外，绝不要写酶被“杀死”——酶没有生命。
Graph shape: a bell-shaped curve. At first the rate rises steadily, reaches a peak at the optimum temperature, then drops steeply to zero at high temperatures.
图形特征：钟形曲线。开始时速率平稳上升，在最适温度达到峰值，然后在高温下急剧下降至零。
4. Effect of pH | pH 的影响
Each enzyme has an optimum pH at which it works fastest. Changes in pH alter the charges on the amino acids that make up the enzyme and break the hydrogen bonds that maintain the active site’s shape. If the pH is too high or too low, the enzyme denatures and the rate falls to zero.
每种酶都有其活性最高的最适 pH。pH 的改变会改变组成酶的氨基酸所带的电荷，并破坏维持活性位点形状的氢键。如果 pH 过高或过低，酶会变性，反应速率降至零。
Most enzymes in the human body work best at a pH near 7 (neutral). However, pepsin, which digests protein in the stomach, has an optimum pH of about 2 because the stomach contains hydrochloric acid. This is a classic example you may be asked to recall.
人体内大多数酶在中性（pH 约 7）附近活性最高。然而，在胃中消化蛋白质的胃蛋白酶，其最适 pH 约为 2，因为胃中含有盐酸。这是一个你可能被要求回忆的经典例子。
In exam graphs, the optimum pH is shown by the peak of the curve. On either side of the peak, the rate falls steeply. Unlike enzyme concentration curves, there is no flat plateau at high pH — the rate always falls to zero at extreme pH values.
在考试的图形中，曲线峰值对应最适 pH。在峰值两侧，速率急剧下降。与酶浓度曲线不同，pH 曲线在极端值处没有平坦的平台——速率在极端 pH 下总是降到零。
5. Substrate and Enzyme Concentration | 底物浓度与酶浓度
At a fixed enzyme concentration, increasing the substrate concentration causes the rate of reaction to rise because there are more substrate molecules to collide with the active sites. However, once all the active sites are occupied at the same time, the enzyme is working at full capacity. Adding more substrate after this point has no further effect, and the rate becomes constant. This maximum rate is called Vₘₐₓ.
在酶浓度固定的情况下，增加底物浓度会使反应速率升高，因为有更多底物分子能与活性位点碰撞。然而，一旦所有活性位点同时被占据，酶就已满负荷工作。此时再增加底物也不会产生更多影响，速率保持不变。这个最大速率称为 Vₘₐₓ。
If you keep substrate in excess and increase the enzyme concentration, the rate increases proportionally. More enzymes mean more active sites, so more enzyme-substrate complexes can form per second. On a graph of rate against enzyme concentration, you should draw a straight line through the origin.
如果在底物过量时增加酶浓度，速率会成比例增加。酶越多，活性位点就越多，每秒能形成的酶-底物复合物也更多。在以酶浓度为横坐标的速率图上，你应该画一条经过原点的直线。
6. Inhibitors | 抑制剂
An inhibitor is a substance that reduces or stops the activity of an enzyme. In competitive inhibition, the inhibitor has a shape very similar to the substrate and competes with the substrate for the active site. If the inhibitor occupies the active site, the substrate cannot bind, so the reaction slows down. This type of inhibition can be reversed by adding more substrate.
抑制剂是能降低或阻止酶活性的物质。在竞争性抑制中，抑制剂的形状与底物非常相似，与底物竞争活性位点。如果抑制剂占据了活性位点，底物就无法结合，反应因此减慢。这种抑制可以通过增加底物浓度来逆转。
In non-competitive inhibition, the inhibitor binds to a different part of the enzyme. This changes the overall shape of the enzyme, including the active site, so the substrate can no longer fit. Adding more substrate does not help, because the active site itself is deformed.
在非竞争性抑制中，抑制剂结合在酶的其他部位。这会改变酶的整体形状，包括活性位点，使底物无法匹配。增加底物也无济于事，因为活性位点本身已经变形。
At IGCSE level, you should also know that heavy metals such as mercury and lead, as well as extreme pH, can act as enzyme inhibitors. This explains why heavy metals are toxic to living organisms.
在 IGCSE 阶段，你还应该知道汞、铅等重金属以及极端 pH 可以作为酶的抑制剂。这就解释了为什么重金属对生物体有毒。
7. Enzymes in Industry | 酶在工业中的应用
Enzymes are widely used in industry because they are specific, work at moderate temperatures, and reduce the need for expensive heating or harsh chemicals. Proteases and lipases are added to biological detergents to break down protein stains and fat or oil stains. They allow stains to be removed at lower temperatures, saving energy.
酶在工业中被广泛应用，因为酶具有特异性、能在温和温度下工作，并且减少了对昂贵加热或强化学试剂的需求。蛋白酶和脂肪酶被加入生物洗涤剂中，用于分解蛋白质污渍和油脂污渍。这样一来，污渍就可以在较低温度下被去除，从而节省能源。
| Enzyme 酶 | Industrial use 工业用途 |
| Protease 蛋白酶 | Removing protein stains in biological detergents 去除生物洗涤剂中的蛋白质污渍 |
| Lipase 脂肪酶 | Removing fat and grease stains in washing powders 去除洗衣粉中的油脂污渍 |
| Pectinase 果胶酶 | Clarifying fruit juices by breaking down pectin 分解果胶以澄清果汁 |
| Glucose isomerase 葡萄糖异构酶 | Converting glucose syrup into sweeter fructose syrup 将葡萄糖浆转化为更甜的果糖浆 |
One key advantage of enzymes is that they work at low temperatures, which saves energy and reduces costs. A second advantage is their high specificity, which means fewer unwanted side reactions and purer products.
酶的一大优点是能在较低温度下工作，从而节省能源、降低成本。第二个优点是特异性强，这意味着副反应更少，产物更纯。
8. Enzymes in Medicine and Daily Life | 酶在医学和日常生活中的应用
Enzymes also play important roles in medicine. Glucose test strips used by people with diabetes contain the enzyme glucose oxidase, which reacts with glucose in the blood to produce a colour change. Some enzymes are used to dissolve blood clots in patients who have had a heart attack or stroke.
酶在医学中也扮演着重要角色。糖尿病患者使用的血糖试纸含有葡萄糖氧化酶，它能与血液中的葡萄糖反应并产生颜色变化。一些酶被用于溶解心脏病发作或中风患者体内的血栓。
In daily life, some people who are lactose intolerant take lactase supplements. Lactase breaks down lactose, the sugar in milk, into glucose and galactose. These supplements allow people to digest dairy products comfortably.
在日常生活中，一些乳糖不耐受的人会服用乳糖酶补充剂。乳糖酶将牛奶中的乳糖分解为葡萄糖和半乳糖。这些补充剂帮助人们顺利消化乳制品。
You should be able to match each enzyme to its use in a table format, and to explain why using enzymes is better than using high temperatures or strong chemicals in terms of both safety and energy saving.
你应该能够将每种酶与其用途一一对应，并且能够从安全和节能两方面解释为什么使用酶比使用高温或强化学试剂更好。
9. Common Exam Mistakes | 常见考试错误
Students often lose marks in enzyme questions because of a small number of repeated mistakes. Learn these now to avoid them in the real exam.
学生在酶相关题目中常常因为少数几个反复出现的错误而丢分。现在就学会避开它们，以免在真正的考试中出错。
-
Saying enzymes are ‘killed’ by heat. Correct term: denatured.
说酶被高温“杀死”。正确术语：变性。
-
Confusing the effect of temperature with the effect of pH. Temperature shows a rise then a sharp drop; pH also shows a rise and drop, but the optimum is specific to each enzyme.
混淆温度与 pH 的影响。温度曲线先升后骤降；pH 曲线同样是先升后降，但最适值因酶而异。
-
Forgetting to label the optimum point on a graph. Always mark it clearly.
在图上忘记标注最适点。一定要清楚标出。
-
Writing that enzymes are used up in reactions. They are not — they are reusable catalysts.
写酶在反应中被消耗掉。酶不会被消耗，它们是可以重复使用的催化剂。
-
Confusing substrate concentration and enzyme concentration graphs. Substrate curve plateaus at Vₘₐₓ; enzyme curve continues to rise linearly if substrate is in excess.
混淆底物浓度曲线和酶浓度曲线。底物曲线在 Vₘₐₓ 处趋于平台；而底物过量时酶浓度曲线持续线性上升。
10. Revision Checklist | 复习清单
Use this checklist to test yourself before your IGCSE Science exam. If you cannot tick an item, go back and revise that section again.
在 IGCSE 科学考试前，用这份清单自测。如果某一项你无法打勾，就回头重新复习那一部分。
-
I can define enzyme, catalyst, substrate, product and active site.
我能定义酶、催化剂、底物、产物和活性位点。
-
I can describe the lock-and-key model and explain why enzymes are specific.
我能描述
Published by TutorHao | IGCSE Science Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
屏轩国际教育cambridge primary/secondary checkpoint, cat4, ukiset,ukcat,igcse,alevel,PAT,STEP,MAT, ibdp,ap,ssat,sat,sat2课程辅导，国外大学本科硕士研究生博士课程论文辅导