Topic 423: Enzymes: Structure, Function and Factors | 主题423：酶的结构、功能与影响因素

📚 Topic 423: Enzymes: Structure, Function and Factors | 主题423：酶的结构、功能与影响因素

Enzymes are biological catalysts that speed up chemical reactions in all living organisms. They are essential for life because they allow reactions to occur rapidly at body temperature and under mild conditions. This topic explores the structure of enzymes, how they work, and the factors that affect their activity.

酶是所有生物体内加速化学反应的生物催化剂。它们对生命至关重要，因为酶能使反应在体温和温和条件下快速进行。本主题探讨酶的结构、作用方式以及影响酶活性的因素。

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1. What Are Enzymes? | 什么是酶？

Enzymes are large proteins made up of long chains of amino acids folded into a specific three-dimensional shape. This shape includes a region called the active site, where the substrate molecule binds and reacts.

酶是由氨基酸长链折叠成特定三维结构的大型蛋白质。该结构包含一个称为活性位点的区域，底物分子在此结合并发生反应。

• Enzymes are specific: each enzyme only works with one type of substrate.

  酶具有专一性：每种酶只作用于一种类型的底物。

• Enzymes are not used up by the reaction, so they can be reused.

  酶在反应中不会被消耗，因此可以重复使用。

• Enzymes are denatured at high temperatures or extreme pH values.

  酶在高温或极端pH条件下会变性。

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2. The Lock and Key Model | 锁钥模型

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

解释酶作用的最常见模型是锁钥模型。底物是钥匙，酶是锁。只有正确的底物才能嵌入活性位点。

Once the substrate binds, the enzyme changes shape slightly to form an enzyme-substrate complex. This lowers the activation energy, allowing the reaction to proceed faster. The product then leaves, and the enzyme is unchanged.

底物结合后，酶的形状发生微小改变，形成酶-底物复合物。这降低了活化能，使反应加速。产物随后离开，酶保持不变。

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

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

Temperature has a major effect on enzyme activity. At low temperatures, molecules move slowly and the rate of reaction is low. As temperature increases, the rate increases because particles have more kinetic energy and more collisions happen per second.

温度对酶活性有重大影响。低温时，分子运动缓慢，反应速率低。随着温度升高，粒子获得更多动能，每秒碰撞次数增加，反应速率加快。

However, there is an optimum temperature (usually around 37 °C in the human body). Above this temperature, the enzyme’s shape begins to change. The active site becomes distorted, so the substrate no longer fits. The enzyme is said to be denatured.

然而，存在一个最适温度（人体内通常约为37 °C）。超过此温度，酶的形状开始改变，活性位点变形，底物不再能结合。此时称酶发生了变性。

Rate increases up to optimum → then decreases sharply after denaturation

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

Each enzyme has an optimum pH at which its activity is highest. For example, pepsin works best in the acidic conditions of the stomach (about pH 2), while amylase works best at neutral pH around 7.

每种酶都有其最适pH，在此pH下活性最高。例如，胃蛋白酶在胃酸环境中（约pH 2）活性最高，而淀粉酶在中性环境（约pH 7）下活性最佳。

Changes in pH alter the charges on the amino acids that make up the enzyme. This disrupts the ionic and hydrogen bonds holding the protein in its shape. At extreme pH values, the enzyme denatures permanently.

pH变化会改变组成酶的氨基酸所带的电荷，破坏维持蛋白质形状的离子键和氢键。在极端pH条件下，酶会永久变性。

• Optimum pH varies for different enzymes.

  不同酶的最适pH不同。

• Buffers are used in experiments to keep pH constant.

  实验中常用缓冲液保持pH恒定。

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5. Measuring Enzyme Activity | 测量酶活性

Enzyme activity can be measured by tracking the rate of product formation or the rate of substrate disappearance. A common experiment uses amylase and starch.

测量酶活性可以通过跟踪产物生成速率或底物消失速率。常见实验使用淀粉酶和淀粉。

To measure the rate, samples are taken at intervals and tested with iodine solution. Iodine turns blue-black in the presence of starch. When the iodine no longer changes colour, all the starch has been broken down.

测量时，每隔一定时间取样并用碘液测试。碘液遇淀粉变蓝黑色。当碘不再变色时，说明淀粉已全部被分解。

Alternatively, the time for the reaction to complete can be measured. A shorter time means a higher rate of reaction.

另一种方法是测定反应完成所需的时间。时间越短，反应速率越高。

Rate = 1 / time taken for reaction to complete

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

Increasing the enzyme concentration increases the rate of reaction up to a point, because more active sites are available for substrate molecules to bind to.

增加酶浓度会在一定限度内提高反应速率，因为可用的活性位点更多，更多底物分子可以结合。

Increasing the substrate concentration also increases the rate, but only until all active sites are occupied. After that, adding more substrate has no effect because the enzyme molecules are saturated.

增加底物浓度同样会提高速率，但直到所有活性位点都被占据为止。此后，再增加底物不会有影响，因为酶分子已饱和。

• At saturation, the only way to increase the rate further is to add more enzyme.

  饱和时，进一步提高速率的唯一方法是添加更多酶。

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7. Enzymes in Digestion | 消化中的酶

Enzymes play crucial roles in digestion. They hydrolyse large, insoluble food molecules into small, soluble ones that can be absorbed into the blood.

酶在消化中起着关键作用。它们将大而不溶于水的食物分子水解为可溶于血液的小分子。

Enzyme	Substrate	Product
Amylase	Starch	Maltose
Protease	Protein	Amino acids
Lipase	Fats	Fatty acids + glycerol

Amylase is produced in the salivary glands and pancreas. Protease is produced in the stomach (pepsin), pancreas and small intestine. Lipase is produced in the pancreas and small intestine.

淀粉酶由唾液腺和胰腺分泌。蛋白酶由胃（胃蛋白酶）、胰腺和小肠分泌。脂肪酶由胰腺和小肠分泌。

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8. Uses of Enzymes in Industry | 酶在工业中的应用

Enzymes are used widely in biotechnology and industry because they work at low temperatures and are specific.

酶在生物技术和工业中广泛应用，因为它们在较低温度下工作且具有专一性。

• Biological detergents: contain proteases and lipases to break down protein and fat stains.

  生物洗涤剂：含有蛋白酶和脂肪酶，用于分解蛋白质和脂肪污渍。

• Fruit juice production: pectinase breaks down pectin in fruit cell walls, increasing juice yield.

  果汁生产：果胶酶分解水果细胞壁中的果胶，提高出汁率。

• Lactose-free products: lactase converts lactose into glucose and galactose for people who are lactose intolerant.

  无乳糖产品：乳糖酶将乳糖转化为葡萄糖和半乳糖，供乳糖不耐受人群使用。

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9. Summary: Key Points for Revision | 总结：复习要点

Enzymes are specific protein catalysts. Their activity depends on temperature and pH. Increasing enzyme or substrate concentration speeds up the reaction, but substrate saturation stops this effect. Denaturation destroys the active site permanently.

酶是专一性的蛋白质催化剂。其活性取决于温度和pH。增加酶或底物浓度会加快反应，但底物饱和会停止这种效应。变性会永久破坏活性位点。

• Enzymes reduce the activation energy of reactions.

  酶降低反应的活化能。

• The lock and key model explains enzyme specificity.

  锁钥模型解释了酶的专一性。

• Optimum conditions vary for each enzyme.

  每种酶都有各自的最适条件。

• Denaturation is irreversible.

  变性是不可逆的。

Remember to practise drawing and interpreting graphs of enzyme activity against temperature and pH. These are common exam questions.

请记住练习绘制和解释酶活性随温度及pH变化的曲线图。这些都是常见考点。

Published by TutorHao | Science Revision Series | aleveler.com

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