📚 Enzymes: The Biological Catalysts | 酶：生物催化剂
Enzymes are essential proteins that speed up chemical reactions in living organisms without being used up themselves. This article covers everything you need to revise for the Edexcel IGCSE Science exam.
酶是生命中至关重要的蛋白质，它们能加速生物体内的化学反应，而自身却不被消耗。本文将帮助您复习 Edexcel IGCSE 科学考试中所有关于酶的核心考点。
1. What Are Enzymes? | 什么是酶？
Enzymes are biological catalysts made of protein. Each enzyme has a specific three-dimensional shape with an active site where substrate molecules bind.
酶是由蛋白质构成的生物催化剂。每种酶都具有特定的三维结构，其中有一个活性位点，用于结合底物分子。
- Catalyst – speeds up a reaction without being changed itself.
- Specific – each enzyme works on only one substrate.
- Reusable – enzymes can be used again after a reaction.
Enzyme + Substrate → Enzyme-Substrate Complex → Enzyme + Product
酶 + 底物 → 酶-底物复合物 → 酶 + 产物
- 催化剂 – 加速反应，自身不发生变化。
- 专一性 – 每种酶只作用于一种底物。
- 可重复使用 – 反应后酶可再次利用。
2. The Lock and Key Model | 锁钥模型
The lock and key model explains enzyme specificity. The active site has a fixed shape that exactly matches the substrate (like a key fits a lock).
锁钥模型解释了酶的专一性。活性位点的形状固定，与底物精确匹配（就像钥匙配锁）。
However, the induced fit model is more accurate – the active site changes shape slightly to fit the substrate more tightly.
然而，诱导契合模型更为准确——活性位点在结合底物时会发生轻微变形，以更紧密地结合底物。
If the substrate does not fit, the reaction cannot occur. This is why enzymes are highly specific.
如果底物不匹配，反应便无法进行。这就是酶具有高度专一性的原因。
3. Factors Affecting Enzyme Activity | 影响酶活性的因素
Enzyme activity is affected by temperature, pH, substrate concentration, and enzyme concentration.
酶活性受温度、pH、底物浓度和酶浓度的影响。
- Temperature – increases reaction rate until the optimum, then decreases.
- pH – each enzyme has an optimum pH; extreme pH denatures it.
- Substrate concentration – rate rises until all active sites are occupied.
- Enzyme concentration – rate rises as more active sites are available.
- 温度 – 在最适温度前反应速率随温度升高而加快，之后则下降。
- pH – 每种酶都有最适 pH；极端 pH 会导致酶变性。
- 底物浓度 – 速率上升直至所有活性位点被占满。
- 酶浓度 – 可用活性位点越多，反应速率越快。
4. Temperature and Enzyme Activity | 温度与酶活性
At low temperatures, molecules move slowly, so enzyme-substrate collisions are rare. As temperature rises, molecules gain kinetic energy and collide more often.
低温下，分子运动缓慢，酶与底物碰撞的机会少。随着温度升高，分子获得动能，碰撞更加频繁。
The optimum temperature for most human enzymes is around 37 °C (body temperature). Above the optimum, bonds in the enzyme break, changing the shape of the active site – this is denaturation.
大多数人体酶的最适温度约为 37 °C（体温）。超过最适温度后，酶内部的化学键断裂，活性位点形状改变——即变性。
Reaction rate → increases to optimum, then drops sharply after denaturation.
反应速率 → 升至最适温度后，因变性而急剧下降。
5. pH and Enzyme Activity | pH 与酶活性
Each enzyme works best at a particular pH. For example, pepsin in the stomach works at pH 2, while trypsin in the intestine works at pH 8.
每种酶都在特定的 pH 下作用最佳。例如，胃中的胃蛋白酶在 pH 2 时工作，而肠道中的胰蛋白酶在 pH 8 时工作。
Changes in pH alter the charges in the enzyme's amino acids, disrupting hydrogen bonds and ionic bonds. This changes the shape of the active site, leading to denaturation at extreme pH values.
pH 变化会改变酶氨基酸上的电荷，破坏氢键和离子键。这会改变活性位点的形状，在极端 pH 下导致变性。
| Enzyme | Optimum pH |
| Pepsin (胃蛋白酶) | 2 |
| Catalase (过氧化氢酶) | 7 |
| Trypsin (胰蛋白酶) | 8 |
6. Denaturation | 变性
Denaturation is the permanent loss of an enzyme's active site shape due to excessive heat or wrong pH. The enzyme cannot bind to its substrate, so the reaction stops.
变性是由于过热或 pH 不当导致酶活性位点形状永久丧失。酶无法与底物结合，反应因此停止。
In denaturation, the peptide bonds remain intact, so the primary structure is unchanged, but the tertiary structure (3D shape) is destroyed.
变性时，肽键仍然完整，一级结构未变，但三级结构（三维形状）被破坏。
Denaturation ≠ broken peptide bonds; it is loss of 3D shape.
变性 ≠ 肽键断裂；而是三维结构丧失。
7. Substrate and Enzyme Concentration | 底物浓度与酶浓度
When enzyme concentration is constant, increasing substrate concentration raises the reaction rate until all active sites are occupied. Further increases have no effect.
当酶浓度恒定时，增加底物浓度会提高反应速率，直到所有活性位点都被占据。再增加底物则无更多效果。
When substrate concentration is in excess, increasing enzyme concentration increases the rate proportionally, because more active sites are available for catalysis.
当底物过量时，增加酶浓度会使速率按比例上升，因为可用的活性位点更多。
- At low substrate: rate is directly proportional to substrate concentration.
- At high substrate: rate plateaus (V-max).
- 在低底物浓度下：速率与底物浓度成正比。
- 在高底物浓度下：速率趋于平缓（最大速率）。
8. Enzyme, Substrate, and Product Names | 常见酶、底物与产物
You should know these classic IGCSE examples:
您需要掌握以下 IGCSE 经典例子：
| 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 脂肪酸和甘油 |
| Catalase 过氧化氢酶 | Hydrogen peroxide 过氧化氢 | Water + oxygen 水和氧气 |
9. Enzymes in Digestion | 消化中的酶
The human digestive system uses enzymes to break down large insoluble molecules into smaller soluble ones that can be absorbed.
人体消化系统利用酶将大分子不溶性物质分解为可吸收的小分子可溶性物质。
- Salivary amylase (mouth) breaks starch into maltose.
- Pepsin (stomach) breaks protein into peptides.
- Pancreatic enzymes (small intestine) break starch, protein, and lipids.
- Maltase, sucrase, lactase (small intestine) break disaccharides into monosaccharides.
- 唾液淀粉酶（口腔）将淀粉分解为麦芽糖。
- 胃蛋白酶（胃）将蛋白质分解为多肽。
- 胰酶（小肠）分解淀粉、蛋白质和脂肪。
- 麦芽糖酶、蔗糖酶、乳糖酶（小肠）将双糖分解为单糖。
10. Uses of Enzymes in Biotechnology | 酶在生物技术中的应用
Enzymes are used in industry due to their specificity and efficiency. For IGCSE, focus on these examples:
酶因其专一性和高效性而广泛应用于工业。IGCSE 考试重点关注以下例子：
- Pectinase – used to clarify fruit juices by breaking down pectin.
- Protease – used in biological washing powders to remove protein stains.
- Lactase – used to produce lactose-free milk.
- Immobilised enzymes – attached to a solid surface so they can be reused easily.
- 果胶酶 – 分解果胶，用于澄清果汁。
- 蛋白酶 – 用于生物洗衣粉，去除蛋白质污渍。
- 乳糖酶 – 用于生产无乳糖牛奶。
- 固定化酶 – 附着在固体表面，便于重复使用。
Advantages of immobilised enzymes: reusable, more stable, product is easier to separate.
固定化酶的优势：可重复使用、更稳定、产物易分离。
Published by TutorHao | Science Revision Series | aleveler.com
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