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

📚 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. They are highly specific and work under particular conditions, making them vital for processes such as digestion, respiration, and photosynthesis.

酶是生物体内不可或缺的蛋白质，它们能加速化学反应，而自身不会被消耗。酶具有高度专一性，并在特定条件下发挥作用，对消化、呼吸和光合作用等过程至关重要。

1. What Are Enzymes? | 什么是酶？

Enzymes are biological catalysts made of protein molecules. Each enzyme has a unique three-dimensional shape with an active site where substrate molecules bind. The reaction then occurs, and the product is released while the enzyme remains unchanged, ready to catalyse another reaction.

酶是由蛋白质分子构成的生物催化剂。每种酶都有独特的三维结构，其中有一个活性位点，底物分子在此结合。随后反应发生，产物被释放，而酶保持不变，可继续催化下一个反应。

The molecule that binds to the enzyme is called the substrate. For example, amylase breaks down starch into maltose, so starch is the substrate. The relationship is often compared to a ‘lock and key’: only the correct substrate fits the enzyme’s active site.

与酶结合的物质称为底物。例如，淀粉酶将淀粉分解为麦芽糖，因此淀粉是底物。这种关系常被比作“锁和钥匙”：只有正确的底物才能与酶的活性位点匹配。

2. The Lock and Key Hypothesis | 锁钥假说

The lock and key hypothesis suggests that the active site of an enzyme has a fixed shape that exactly complements the substrate. When the substrate binds, an enzyme-substrate complex forms, and the reaction proceeds rapidly. This explains why enzymes are highly specific — only one type of substrate fits each enzyme.

锁钥假说认为，酶的活性位点具有固定的形状，与底物完全互补。当底物结合时，形成酶-底物复合物，反应迅速进行。这解释了酶的高度专一性——每种酶只能匹配一种类型的底物。

However, modern research shows that the active site is slightly flexible. The induced fit model is an update: the enzyme changes shape slightly to accommodate the substrate, like a glove moulding to a hand. Still, the lock and key model is a useful simplification for understanding enzyme specificity.

然而，现代研究表明活性位点具有一定柔性。诱导契合模型是更新的观点：酶的形状会略微改变以适应底物，就像手套贴合手形一样。尽管如此，锁钥假说仍是理解酶专一性的有效简化模型。

3. Enzyme-Substrate Complex | 酶-底物复合物

When a substrate binds to the active site, the enzyme and substrate temporarily join to form an enzyme-substrate complex. During this time, chemical bonds in the substrate are weakened, lowering the activation energy needed for the reaction. This speeds up the reaction dramatically.

当底物与活性位点结合时，酶和底物暂时连接形成酶-底物复合物。在此过程中，底物内部的化学键被削弱，从而降低了反应所需的活化能，大大加快了反应速度。

For example, catalase breaks down hydrogen peroxide into water and oxygen. The enzyme-substrate complex forms almost instantly, releasing oxygen gas. Without catalase, this reaction would be extremely slow at body temperature.

例如，过氧化氢酶将过氧化氢分解为水和氧气。酶-底物复合物几乎瞬间形成，并释放氧气。没有过氧化氢酶，该反应在体温下将极其缓慢。

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

Temperature affects the kinetic energy of molecules. As temperature increases, molecules move faster and collide more often, increasing the rate of enzyme-substrate complex formation. The rate rises up to an optimum temperature, usually around 37°C in human enzymes.

温度影响分子的动能。随着温度升高，分子运动加快，碰撞频率增加，从而提高了酶-底物复合物的形成速率。反应速率上升到最适温度，人体酶通常约为37°C。

Above the optimum temperature, the enzyme’s structure begins to denature. The vibrations break hydrogen bonds that hold the protein in shape, causing the active site to change shape permanently. The enzyme can no longer bind to its substrate, and the reaction stops.

超过最适温度后，酶的结构开始变性。振动会破坏维持蛋白质形状的氢键，导致活性位点永久改变形状。酶无法再与底物结合，反应随之停止。

Rate of reaction ↑ as temperature ↑ → optimum → rapid ↓ after denaturation

反应速率随温度升高而上升 → 达到最适温度 → 变性后急剧下降

5. 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 in the stomach works best at pH 2, while trypsin in the small intestine works best at pH 8. Changes in pH alter the charges on amino acid residues and can disrupt the enzyme’s shape.

每种酶都有其最适pH，此时活性最高。例如，胃中的胃蛋白酶在pH 2时活性最强，而小肠中的胰蛋白酶在pH 8时活性最强。pH的改变会影响氨基酸残基的电荷，从而破坏酶的形状。

If the pH is too high or too low, hydrogen bonds and ionic bonds within the enzyme break, leading to denaturation. The active site changes shape, and the enzyme cannot function. Unlike temperature denaturation, extreme pH denaturation is also irreversible in most cases.

如果pH过高或过低，酶内部的氢键和离子键会被破坏，导致变性。活性位点形状改变，酶无法发挥作用。与温度变性类似，极端pH导致的变性在大多数情况下也是不可逆的。

6. Factors Affecting Enzyme Activity: Substrate Concentration | 影响酶活性的因素：底物浓度

As substrate concentration increases, the rate of reaction increases because more substrate molecules are available to collide with the enzyme active sites. However, this only happens up to a point. Once all active sites are occupied, the enzyme is saturated.

随着底物浓度增加，反应速率加快，因为更多的底物分子可与酶活性位点碰撞。但这种情况只在一定范围内成立。一旦所有活性位点都被占据，酶便达到饱和。

At saturation, adding more substrate does not increase the rate further. The only way to speed up the reaction is to add more enzyme molecules. This principle is important in industrial and biological systems where enzyme concentration is limited.

在饱和状态下，增加更多底物也不能进一步提高反应速率。唯一的加速方法是增加更多的酶分子。这一原理在酶浓度受限的工业和生物系统中尤为重要。

7. Enzyme Concentration | 酶浓度

When substrate is in excess, increasing enzyme concentration increases the rate of reaction proportionally. More enzymes mean more active sites available for substrate molecules to bind, so more product is formed per unit time.

当底物过量时，增加酶浓度会使反应速率按比例增加。更多的酶意味着有更多活性位点可供底物结合，因此单位时间内生成更多产物。

Eventually, the rate may plateau if other factors, such as substrate concentration or time, become limiting. In a closed system, the reaction will slow down as substrate is consumed, and the product may even inhibit the enzyme in some cases.

最终，如果其他因素（如底物浓度或时间）成为限制因素，反应速率可能会达到平台期。在封闭体系中，随着底物被消耗，反应会减慢，某些情况下产物甚至可能抑制酶活性。

8. Denaturation | 变性

Denaturation is a permanent change in the three-dimensional structure of an enzyme, leading to loss of its biological activity. High temperatures, extreme pH values, and exposure to heavy metals can cause denaturation. The peptide bonds remain intact, but the protein unfolds.

变性是酶三维结构的永久性改变，导致其失去生物活性。高温、极端pH值和重金属暴露均可引起变性。肽键仍然完整，但蛋白质结构展开。

Once denatured, the active site is no longer complementary to the substrate. Even if conditions return to normal, the enzyme cannot recover its original shape. This is why fever above 40°C can be dangerous — vital enzymes in the body begin to denature.

一旦变性，活性位点便不再与底物互补。即使条件恢复正常，酶也无法恢复其原始形状。这就是为什么超过40°C的高烧很危险——体内重要的酶开始变性。

9. Enzymes in Digestion | 消化中的酶

Digestion relies on several enzymes. Amylase in saliva and pancreatic juice breaks down starch into maltose. Proteases, such as pepsin and trypsin, hydrolyse proteins into amino acids. Lipases break down fats into fatty acids and glycerol. These reactions occur at different body sites with different pH optima.

消化过程依赖多种酶。唾液和胰液中的淀粉酶将淀粉分解为麦芽糖。蛋白酶（如胃蛋白酶和胰蛋白酶）将蛋白质水解为氨基酸。脂肪酶将脂肪分解为脂肪酸和甘油。这些反应发生在体内不同部位，各有不同的最适pH。

Bile, produced by the liver, is not an enzyme but helps emulsify fats, increasing the surface area for lipase to act. The coordinated action of enzymes and bile ensures efficient absorption of nutrients in the small intestine.

肝脏产生的胆汁不是酶，但它有助于乳化脂肪，增加脂肪酶作用的表面积。酶和胆汁的协同作用确保小肠对营养物质的有效吸收。

10. Industrial Use of Enzymes | 酶的工业应用

Enzymes are widely used in industry because they are specific, efficient, and environmentally friendly. For example, biological washing powders contain proteases and lipases to remove protein and fat stains at moderate temperatures. This saves energy compared to hot washing.

酶在工业中被广泛使用，因为它们专一、高效且环保。例如，加酶洗衣粉含有蛋白酶和脂肪酶，可在适中温度下去除蛋白质和脂肪污渍。与热水洗涤相比，这能节约能源。

In food production, enzymes like rennet are used to make cheese, and invertase is used to produce soft-centred chocolates. In medicine, enzymes such as streptokinase help dissolve blood clots. Enzymes offer a greener alternative to harsh chemical catalysts.

在食品生产中，凝乳酶用于制作奶酪，转化酶用于生产软心巧克力。在医学中，链激酶等酶有助于溶解血栓。酶比刺激性化学催化剂更环保。

11. Investigations on Enzyme Activity | 酶活性实验探究

A common IGCSE investigation measures the rate of breakdown of hydrogen peroxide by catalase. You can collect the oxygen gas produced and measure the volume per unit time. Changing temperature or pH while keeping everything else constant shows how these factors affect the rate.

一个常见的IGCSE实验是测量过氧化氢酶分解过氧化氢的速率。你可以收集产生的氧气并测量单位时间内的体积。在保持其他条件不变的情况下改变温度或pH，可以观察这些因素对速率的影响。

When testing temperature, remember to allow the enzyme and substrate to reach the target temperature separately before mixing. This prevents the reaction from occurring before the desired temperature is reached. Repeat experiments and calculate averages for reliability.

测试温度时，应让酶和底物分别达到目标温度后再混合，以防止反应在到达设定温度前就发生。重复实验并计算平均值以确保可靠性。

12. Key Points for Revision | 复习要点

Remember that enzymes are specific catalysts with an active site. Temperature and pH affect enzyme activity through changes in shape, with extremes causing denaturation. Substrate and enzyme concentration affect the rate until saturation or exhaustion. Use graphs to interpret these relationships.

请记住：酶是具有活性位点的专一催化剂。温度和pH通过改变形状影响酶活性，极端情况会导致变性。底物和酶浓度影响反应速率，直到饱和或耗尽。要会用图表来解释这些关系。

In exams, always refer to the ‘enzyme-substrate complex’ and ‘active site’ in your answers. For rate questions, state that rate increases until the optimum, then decreases sharply due to denaturation. For concentration questions, mention saturation of active sites. These precise phrases earn marks.

在考试中，回答时要提到“酶-底物复合物”和“活性位点”。对于速率问题，说明速率上升到最适点后因变性而急剧下降。对于浓度问题，提到活性位点的饱和。使用这些精确术语可以获得分数。

Published by TutorHao | Science Revision Series | aleveler.com

更多咨询请联系16621398022（同微信）

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