Enzymes | 酶

📚 Enzymes | 酶

Enzymes are biological catalysts that speed up chemical reactions in living organisms without being used up in the process. They are essential for almost every metabolic reaction, from digestion to DNA replication.

酶是生物催化剂，能在生物体内加速化学反应，而自身在反应过程中不被消耗。几乎每一种代谢反应——从消化到DNA复制——都离不开酶的参与。

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1. What Are Enzymes? | 什么是酶？

Enzymes are globular proteins made up of long chains of amino acids folded into a specific three-dimensional shape. This shape includes an active site where substrate molecules bind.

酶是由氨基酸长链折叠成的特定三维形状的球状蛋白质。该形状包含一个活性位点，底物分子在此结合。

• Enzymes are specific – each enzyme catalyses only one reaction or type of reaction.
• 酶的专一性——每种酶只催化一种或一类反应。
• Enzymes are not changed permanently by the reaction and can be reused.
• 酶在反应后不会发生永久改变，可以被重复利用。
• Enzymes lower the activation energy needed for a reaction.
• 酶能降低反应所需的活化能。

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2. The Lock and Key Model | 锁钥模型

The lock and key model describes enzyme action: the substrate fits into the active site like a key fits into a lock. Only the correct substrate can bind to the active site.

锁钥模型描述酶的作用方式：底物像钥匙插入锁孔一样进入活性位点。只有正确的底物才能与活性位点结合。

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

酶 + 底物 → 酶-底物复合物 → 酶 + 产物

Once the enzyme-substrate complex forms, the reaction occurs, and the products are released, leaving the enzyme unchanged.

一旦形成酶-底物复合物，反应随即发生，产物被释放，酶保持不变。

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3. Enzyme Specificity | 酶的专一性

Enzyme specificity is due to the unique shape of the active site. The active site has a precise arrangement of amino acid residues that interact with the substrate through weak bonds.

酶的专一性源于活性位点的独特形状。活性位点的氨基酸残基通过弱键与底物发生精确的相互作用。

• Amylase acts on starch, not on protein or fat.
• 淀粉酶作用于淀粉，而不作用于蛋白质或脂肪。
• Protease acts on proteins, breaking them into amino acids.
• 蛋白酶作用于蛋白质，将其分解为氨基酸。
• Lipase acts on fats (lipids) to produce fatty acids and glycerol.
• 脂肪酶作用于脂肪（脂质），生成脂肪酸和甘油。

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4. Effect of Temperature | 温度的影响

Temperature affects the rate of enzyme-controlled reactions. As temperature increases, particles move faster, and more collisions occur between enzyme and substrate, so the rate increases.

温度影响酶促反应的速率。随着温度升高，分子运动加快，酶与底物之间的碰撞增多，反应速率加快。

Q₁₀ ≈ 2 for many enzyme reactions (rate doubles for every 10 °C rise, up to optimum)

许多酶反应的温度系数Q₁₀ ≈ 2（在到达最适温度前，温度每升高10 °C，速率约加倍）

However, above the optimum temperature (often 37 °C in humans), the enzyme begins to denature. Denaturation alters the shape of the active site, so the substrate can no longer bind.

然而，一旦超过最适温度（人体内通常为37 °C），酶开始变性。变性改变活性位点的形状，底物无法再结合。

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5. Effect of pH | pH的影响

Each enzyme has an optimum pH. Changes in pH affect the charges on amino acid residues and the hydrogen bonds that maintain the enzyme’s structure, disrupting the active site.

每种酶都有最适pH。pH的变化会影响氨基酸残基的电荷以及维持酶结构的氢键，从而破坏活性位点。

• Pepsin in the stomach works best at pH 2.
• 胃中的胃蛋白酶在pH 2时活性最强。
• Amylase in the mouth and small intestine works best at pH 7–8.
• 口腔和小肠中的淀粉酶在pH 7–8时活性最强。

Extreme pH values cause denaturation, just like high temperature.

极端的pH值同样会导致酶变性，与高温类似。

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6. Effect of Substrate Concentration | 底物浓度的影响

As substrate concentration increases, the rate of reaction increases because more substrate molecules are available to occupy active sites. However, once all active sites are occupied, the enzyme is saturated, and the rate plateaus.

随着底物浓度增加，反应速率加快，因为更多底物分子可供活性位点结合。然而，当所有活性位点都被占据时，酶达到饱和，反应速率不再增加，出现平台期。

Rate ∝ [S] (at low [S]); Rate = V_max (at saturation)

低底物浓度时，速率 ∝ [S]；饱和时，速率 = V_max

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7. Effect of Enzyme Concentration | 酶浓度的影响

When substrate is present in excess, increasing enzyme concentration increases the number of active sites available, so the rate of reaction increases proportionally.

当底物过量时，增加酶浓度会增加可用的活性位点数量，因此反应速率按比例提高。

If enzyme concentration is doubled, the rate is expected to double, provided substrate is not limiting.

如果酶浓度加倍，在底物不限制的前提下，反应速率预计也会加倍。

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8. Competitive Inhibition | 竞争性抑制

A competitive inhibitor has a shape similar to the substrate and competes for the active site. It blocks the active site temporarily, reducing the rate of reaction.

竞争性抑制剂具有与底物相似的形状，并争夺活性位点。它暂时占据活性位点，从而降低反应速率。

• Increasing substrate concentration can overcome competitive inhibition.
• 增加底物浓度可以克服竞争性抑制。
• An example is malonate competing with succinate in the Krebs cycle.
• 例如丙二酸在克雷布斯循环中与琥珀酸竞争。

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9. Non-Competitive Inhibition | 非竞争性抑制

A non-competitive inhibitor binds to a site other than the active site (an allosteric site). This changes the enzyme’s shape, including the active site, so the substrate cannot bind effectively.

非竞争性抑制剂结合在活性位点以外的位点（变构位点）。这会改变酶的整体形状，包括活性位点，使底物无法有效结合。

Increasing substrate concentration does not fully overcome non-competitive inhibition because the enzyme is permanently altered.

增加底物浓度不能完全克服非竞争性抑制，因为酶已经发生不可逆改变。

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10. Enzymes in Digestion | 消化中的酶

Digestive enzymes break down large insoluble food molecules into small soluble molecules that can be absorbed into the blood.

消化酶将大的不溶性食物分子分解成可被血液吸收的小分子可溶性物质。

Enzyme	Substrate	Product
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	Fat / lipid 脂肪/脂质	Fatty acids + glycerol 脂肪酸 + 甘油

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11. Enzymes in Industry and Medicine | 酶在工业和医药中的应用

Enzymes are widely used in biological washing powders, food production, and medical diagnostics.

酶广泛应用于生物洗衣粉、食品生产和医学诊断中。

• Proteases and lipases in biological detergents break down protein and fat stains at low temperatures.
• 生物洗涤剂中的蛋白酶和脂肪酶可在低温下分解蛋白质和脂肪污渍。
• Lactase is used to produce lactose-free milk for people with lactose intolerance.
• 乳糖酶用于生产无乳糖牛奶，供乳糖不耐受人群食用。
• Enzyme biosensors, such as glucose meters, use glucose oxidase to measure blood sugar.
• 酶生物传感器（如血糖仪）利用葡萄糖氧化酶测量血糖。

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12. Denaturation | 变性

Denaturation is the permanent change in the three-dimensional structure of an enzyme, causing the active site to lose its shape. The enzyme can no longer function.

变性是指酶的三维结构发生永久性改变，导致活性位点失去原有形状。酶因此无法再发挥功能。

Denaturation can be caused by high temperature, extreme pH, or exposure to heavy metals. It is irreversible.

高温、极端pH或重金属接触均可导致变性。变性是不可逆的。

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Published by TutorHao | Biology Revision Series | aleveler.com

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