Enzymes: Catalysts of Life | 酶：生命的催化剂

📚 Enzymes: Catalysts of Life | 酶：生命的催化剂

Enzymes are biological molecules that speed up chemical reactions in living organisms. They are essential for processes such as digestion, respiration, and photosynthesis. Without enzymes, most reactions in cells would be too slow to sustain life.

酶是生物体内能够加速化学反应的生物分子。它们对消化、呼吸和光合作用等过程至关重要。没有酶，细胞中的大多数反应将慢得无法维持生命。

1. What Are Enzymes? | 什么是酶？

Enzymes are proteins made of long chains of amino acids folded into specific three-dimensional shapes. Each enzyme has a unique shape that allows it to carry out a particular function. The shape of an enzyme is crucial because it determines which substrate the enzyme can bind to.

酶是由氨基酸长链折叠成特定三维形状的蛋白质。每种酶都有独特的形状，使其能够执行特定的功能。酶的形状至关重要，因为它决定了酶能结合哪种底物。

The substance on which an enzyme acts is called the substrate. The site where the substrate binds is called the active site. The active site is a small region of the enzyme with a shape complementary to the substrate.

酶作用的物质称为底物。底物结合的位置称为活性位点。活性位点是酶上的一小部分区域，其形状与底物互补。

Enzymes are biological catalysts.
酶是生物催化剂。
They are not used up in reactions.
它们在反应中不会被消耗。

2. The Structure of Enzymes | 酶的结构

Enzymes are made of amino acids linked by peptide bonds. The sequence of amino acids determines how the protein folds. Folding creates a globular shape with an active site on the surface. Hydrogen bonds and other interactions hold the structure together.

酶由氨基酸通过肽键连接而成。氨基酸序列决定了蛋白质如何折叠。折叠形成球状形状，表面有活性位点。氢键和其他相互作用维持其结构。

Any change in temperature or pH can break these bonds, especially the hydrogen bonds. When the bonds break, the enzyme changes shape and stops working. This permanent change is called denaturation.

温度或 pH 的任何变化都可能破坏这些键，尤其是氢键。当键断裂时，酶会改变形状并停止工作。这种永久性变化称为变性。

Amino acids → Polypeptide chain → Folded protein → Enzyme

氨基酸 → 多肽链 → 折叠蛋白质 → 酶

3. How Enzymes Work: Lock and Key | 酶的工作原理：锁钥模型

The most common model for enzyme action is the lock and key model. The enzyme is the lock, and the substrate is the key. Only the correct key fits into the lock, so only the correct substrate can bind to the active site.

最常见的酶作用模型是锁钥模型。酶是锁，底物是钥匙。只有正确的钥匙才能插入锁中，因此只有正确的底物才能与活性位点结合。

When the substrate binds to the active site, an enzyme-substrate complex is formed. The reaction takes place, and the products are released. The enzyme is unchanged and can be reused.

当底物与活性位点结合时，会形成酶-底物复合体。反应发生，产物释放。酶不变并可重复使用。

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

酶 + 底物 → 酶-底物复合体 → 酶 + 产物

4. Enzyme Specificity | 酶的专一性

Enzymes are highly specific. Each enzyme only catalyses one reaction or a small group of reactions. This is because the active site has a specific shape that only fits one substrate, just like a key fits a lock.

酶具有高度专一性。每种酶只催化一种反应或一小类反应。这是因为活性位点具有特定的形状，只适合一种底物，就像钥匙配锁一样。

For example, amylase only breaks down starch, and lipase only breaks down fats. Protease only breaks down proteins. If the substrate does not fit the active site, no reaction occurs.

例如，淀粉酶只分解淀粉，脂肪酶只分解脂肪。蛋白酶只分解蛋白质。如果底物与活性位点不匹配，反应就不会发生。

5. Effect of Temperature | 温度的影响

Temperature has a significant effect on enzyme activity. As temperature increases, particles move faster and collide more often, so the rate of reaction increases. The optimum temperature is the temperature at which the enzyme works fastest.

温度对酶活性有显著影响。随着温度升高，粒子运动加快，碰撞更频繁，因此反应速率增加。最适温度是酶工作最快的温度。

Temperature / 温度	Effect on Enzyme Activity / 对酶活性的影响
Low / 低	Slow reaction rate / 反应速率慢
Optimum (e.g. 37 °C in humans) / 最适（如人体 37 °C）	Maximum activity / 活性最大
High (above optimum) / 高（超过最适）	Denaturation occurs / 发生变性

For most human enzymes, the optimum temperature is about 37 °C. Above this temperature, the enzyme begins to denature. The active site changes shape and the substrate can no longer bind.

对于大多数人体酶，最适温度约为 37 °C。超过此温度，酶开始变性。活性位点形状改变，底物无法再结合。

6. Effect of pH | pH 的影响

Enzymes also have an optimum pH. Most enzymes work best in neutral conditions (pH 7), but some have different optima. For example, pepsin in the stomach works best at pH 2, while trypsin works best at pH 8.

酶也有最适 pH。大多数酶在中性条件（pH 7）下工作最佳，但有些酶的最适 pH 不同。例如，胃中的胃蛋白酶在 pH 2 时工作最佳，而胰蛋白酶在 pH 8 时最佳。

If the pH is above or below the optimum, the rate of reaction decreases. Extreme pH changes break the bonds that maintain the enzyme’s shape, leading to denaturation.

如果 pH 高于或低于最适值，反应速率会下降。极端的 pH 变化会破坏维持酶形状的键，导致变性。

pH too high or too low → Denaturation → Loss of enzyme activity

pH 过高或过低 → 变性 → 酶活性丧失

7. Substrate and Enzyme Concentration | 底物浓度和酶浓度

Enzyme concentration affects the rate of reaction. As enzyme concentration increases, the rate of reaction increases, provided there is enough substrate. Eventually, a point is reached where the substrate is used up quickly and the rate slows down.

酶浓度影响反应速率。随着酶浓度增加，反应速率增加，前提是有足够的底物。最终会达到一个点，底物被迅速消耗，速率减慢。

Substrate concentration also matters. Increasing substrate concentration at a fixed enzyme concentration increases the rate until all active sites are occupied. At that point, the rate becomes constant because the enzymes are saturated.

底物浓度也很重要。在酶浓度固定时增加底物浓度，速率会提高，直到所有活性位点都被占据。此时速率保持恒定，因为酶已饱和。

More enzyme → more active sites → faster rate.
更多酶 → 更多活性位点 → 更快速率。
More substrate → more collisions → faster rate up to a limit.
更多底物 → 更多碰撞 → 速率提高至极限。

8. Enzyme Denaturation | 酶的变性

Denaturation is a permanent change in the three-dimensional shape of an enzyme. It occurs when the protein structure is disrupted by high temperature or extreme pH. The hydrogen bonds that hold the enzyme in shape break, and the active site is destroyed.

变性是酶三维形状的永久改变。当高温或极端 pH 破坏蛋白质结构时就会发生。维持酶形状的氢键断裂，活性位点被破坏。

A denatured enzyme can no longer catalyse reactions because its active site no longer fits the substrate. This process is irreversible. Cooking an egg is an example of protein denaturation.

变性的酶无法再催化反应，因为其活性位点不再适合底物。这个过程是不可逆的。煮鸡蛋就是蛋白质变性的一个例子。

9. Enzymes in Digestion | 消化中的酶

Digestive enzymes break down large food molecules into small soluble molecules that can be absorbed into the blood. Each enzyme targets a specific food group.

消化酶将大的食物分子分解为可吸收进入血液的小的可溶分子。每种酶针对特定的食物类别。

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	Lipids / 脂质	Fatty acids + glycerol / 脂肪酸 + 甘油

Amylase is produced in the salivary glands and pancreas. Protease and lipase are mainly produced in the pancreas and small intestine.

淀粉酶由唾液腺和胰腺产生。蛋白酶和脂肪酶主要由胰腺和小肠产生。

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

Enzymes are widely used in industry and medicine. They are used because they are specific, work at mild temperatures, and are biodegradable. This makes them more environmentally friendly than many chemical catalysts.

酶广泛应用于工业和医学。它们被使用是因为具有专一性、能在温和温度下工作，并且可生物降解。这使得它们比许多化学催化剂更环保。

Biological washing powders: contain proteases and lipases to remove stains.
生物洗衣粉：含有蛋白酶和脂肪酶来去除污渍。
Cheese production: uses rennin to clot milk.
奶酪生产：使用凝乳酶使牛奶凝结。
Glucose production: amylase converts starch into sugar.
葡萄糖生产：淀粉酶将淀粉转化为糖。

11. Investigating Enzymes: Practical Work | 酶的研究：实验

The effect of temperature on enzyme activity can be investigated using amylase and starch. Starch is detected with iodine solution; it turns from orange-brown to blue-black in the presence of starch. If starch is broken down, the iodine remains orange-brown.

可以使用淀粉酶和淀粉来研究温度对酶活性的影响。淀粉用碘液检测；有淀粉时碘液从橙棕色变为蓝黑色。如果淀粉被分解，碘液保持橙棕色。

Steps: add amylase and starch to a test tube at a set temperature. Take samples every minute and add iodine. Measure how long it takes for starch to disappear. Repeat at different temperatures.

步骤：在设定温度下向试管中加入淀粉酶和淀粉。每分钟取样并加入碘液。测量淀粉消失所需的时间。在不同温度下重复。

The optimum temperature is where starch disappears fastest. At high temperatures, starch may not disappear because the enzyme is denatured.

最适温度是淀粉消失最快时的温度。在高温下，淀粉可能不会消失，因为酶已经变性。

12. Key Exam Summary | 考点总结

Remember the key points: enzymes are biological catalysts made of protein. They have an active site that is specific to one substrate. Temperature and pH affect activity; extreme conditions cause denaturation. Enzymes remain unchanged after a reaction.

记住要点：酶是由蛋白质组成的生物催化剂。它们有一个对一种底物专一的活性位点。温度和 pH 影响活性；极端条件导致变性。酶在反应后保持不变。

In the exam, make sure you can describe the lock and key model, interpret graphs of enzyme activity, and state examples of digestive enzymes and their substrates.

考试中，请确保你能描述锁钥模型、解释酶活性图表，并说出消化酶及其底物的例子。

Enzyme = Catalyst = Speeds up reaction = Reusable

酶 = 催化剂 = 加速反应 = 可重复使用

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Enzymes: Catalysts of Life | 酶：生命的催化剂