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

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

Enzymes are specialised proteins that act as biological catalysts, speeding up chemical reactions without being used up themselves. They are essential for almost every process in living organisms, from digestion to DNA replication.

酶是特殊的蛋白质，作为生物催化剂，能加速化学反应，而自身不会被消耗。它们几乎参与生物体内的所有过程，从消化到DNA复制都至关重要。

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1. What Are Enzymes? | 什么是酶？

An enzyme is a globular protein with a unique three-dimensional shape. Each enzyme has an active site where specific substrate molecules bind. The ‘lock and key’ model describes this specificity: only the correct substrate fits into the active site, just like a key fits a specific lock.

酶是一种具有独特三维形状的球状蛋白质。每种酶都有一个活性位点，特定的底物分子在此结合。”锁钥模型”描述了这种专一性：只有正确的底物才能与活性位点结合，就像特定的钥匙只能打开对应的锁一样。

• Protein nature: Enzymes are made of amino acid chains folded into complex shapes.

• Active site: A small region on the enzyme surface where catalysis occurs.

• Substrate: The reactant molecule that binds to the active site.

• 蛋白质本质：酶由氨基酸链折叠成复杂形状构成。

• 活性位点：酶表面发生催化作用的小区域。

• 底物：与活性位点结合的反应物分子。

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2. The Lock and Key Model | 锁钥模型

In the lock and key model, the enzyme is the ‘lock’ and the substrate is the ‘key’. The substrate fits exactly into the active site, forming an enzyme-substrate complex. This specific fit ensures that each enzyme only catalyses one type of reaction.

在锁钥模型中，酶是”锁”，底物是”钥匙”。底物精确地嵌入活性位点，形成酶-底物复合物。这种精确匹配确保了每种酶只催化一种类型的反应。

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

酶 + 底物 ⇌ 酶-底物复合物 → 产物 + 酶

After the reaction, the products are released, and the enzyme remains unchanged, ready to catalyse another reaction.

反应结束后，产物被释放，酶保持不变，可继续催化下一个反应。

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3. Enzyme Specificity | 酶的专一性

Enzymes are highly specific. For example, sucrase only breaks down sucrose, while protease only breaks down proteins. This specificity is due to the precise shape of the active site, which matches only one substrate under normal conditions.

酶具有高度专一性。例如，蔗糖酶只分解蔗糖，而蛋白酶只分解蛋白质。这种专一性源于活性位点的精确形状，在正常条件下只匹配一种底物。

Enzyme | 酶	Substrate | 底物	Product(s) | 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

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

Temperature has a significant effect on enzyme activity. As temperature rises, molecules move faster, increasing the chance of enzyme-substrate collisions. The rate of reaction therefore increases up to an optimum temperature (usually around 37°C in humans).

温度对酶活性有显著影响。随着温度升高，分子运动加快，酶与底物碰撞的机会增加。因此，反应速率在达到最适温度（人体内通常约为37°C）之前持续上升。

However, above the optimum temperature, the enzyme’s bonds begin to break. The active site changes shape and the enzyme becomes denatured. The substrate can no longer bind, and the reaction slows dramatically or stops.

然而，超过最适温度后，酶的化学键开始断裂，活性位点形状改变，酶发生变性。底物无法再结合，反应速率急剧下降甚至停止。

Optimum temperature ≈ 37°C (human enzymes) | 最适温度 ≈ 37°C（人体酶）

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

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

酶也有最适pH。大多数人体酶在pH 7（中性）时活性最强，但有些酶例外。例如，胃中的胃蛋白酶最适pH为2，小肠中的胰蛋白酶最适pH为8。

If the pH deviates too far from the optimum, hydrogen bonds are disrupted, altering the enzyme’s shape and causing denaturation. This is often permanent.

如果pH偏离最适值过大，氢键会被破坏，改变酶的形状并导致变性。这种变性通常是不可逆的。

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6. Enzymes and Metabolic Reactions | 酶与代谢反应

Metabolic reactions are either anabolic (building larger molecules) or catabolic (breaking down larger molecules). Enzymes control both types. For example, DNA polymerase builds new DNA strands during replication, while catalase breaks down hydrogen peroxide into water and oxygen.

代谢反应分为合成代谢（构建大分子）和分解代谢（分解大分子）。酶控制这两类反应。例如，DNA聚合酶在复制过程中构建新的DNA链，而过氧化氢酶将过氧化氢分解为水和氧气。

2H₂O₂ → 2H₂O + O₂

Catalase is one of the fastest enzymes known, protecting cells from toxic hydrogen peroxide.

过氧化氢酶是已知最快的酶之一，保护细胞免受有毒过氧化氢的伤害。

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7. Enzymes in Digestion | 消化中的酶

Digestive enzymes are secreted along the alimentary canal. Salivary amylase breaks down starch in the mouth, pepsin digests proteins in the stomach, and pancreatic enzymes continue digestion in the small intestine.

消化酶沿消化道分泌。唾液淀粉酶在口腔中分解淀粉，胃蛋白酶在胃中消化蛋白质，胰酶在小肠中继续消化。

• Amylase: Starch → Maltose

• Protease: Proteins → Amino acids

• Lipase: Lipids → Fatty acids + Glycerol

• 淀粉酶：淀粉 → 麦芽糖

• 蛋白酶：蛋白质 → 氨基酸

• 脂肪酶：脂质 → 脂肪酸 + 甘油

Bile, produced by the liver, is not an enzyme. It emulsifies fats, increasing the surface area for lipase to work on.

肝脏分泌的胆汁不是酶。它乳化脂肪，增大脂肪与脂肪酶作用的表面积。

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8. Industrial and Medical Uses of Enzymes | 酶在工业和医疗中的应用

Enzymes are widely used in biotechnology. Biological detergents contain proteases and lipases to remove stains. In medicine, enzymes are used to diagnose diseases, such as testing for cardiac enzymes after a heart attack.

酶在生物技术中被广泛使用。加酶洗涤剂含有蛋白酶和脂肪酶以去除污渍。在医学上，酶用于诊断疾病，例如心脏病发作后检测心肌酶。

Enzymes are also used in food production. For example, rennet contains enzymes that help make cheese, and invertase is used to soften chocolate centres.

酶也用于食品生产。例如，凝乳酶中的酶帮助制作奶酪，转化酶用于软化巧克力夹心。

However, enzymes can be sensitive to conditions. Industrial processes must maintain optimal temperature and pH to keep enzymes active.

然而，酶对环境条件敏感。工业过程必须维持最适温度和pH以保持酶活性。

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Published by TutorHao | Biology Revision Series | aleveler.com

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