Enzymes in Action: How Biological Catalysts Work | 酶的作用：生物催化剂的工作原理

📚 Enzymes in Action: How Biological Catalysts Work | 酶的作用：生物催化剂的工作原理

Enzymes are remarkable biological molecules that accelerate chemical reactions in living organisms, acting as catalysts to sustain life. In the Edexcel IGCSE Science syllabus, understanding enzymes is essential for topics in biology and chemistry, from digestion to industrial processes.

酶是神奇的生物分子，它们作为催化剂加速生物体内的化学反应，维持生命的运转。在Edexcel IGCSE科学大纲中，理解酶对于从消化到工业过程等生物和化学主题至关重要。

1. What Are Enzymes? | 什么是酶？

Enzymes are biological catalysts, usually proteins, that speed up chemical reactions without being used up in the process. They are essential for life because most metabolic reactions would be too slow at body temperature without them.

酶是生物催化剂，通常是蛋白质，它们能加快化学反应速率，而自身在反应中不被消耗。酶对生命至关重要，因为大多数代谢反应在没有酶的情况下，在体温下会慢得无法维持生命。

Enzymes are highly specific, meaning each enzyme only catalyses one type of reaction. For example, amylase breaks down starch into maltose but does not affect proteins or lipids.

酶具有高度特异性，即每种酶只催化一种类型的反应。例如，淀粉酶将淀粉分解为麦芽糖，但不影响蛋白质或脂质。

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2. The Active Site and Substrate Specificity | 活性位点与底物特异性

The active site is a specially shaped region on the enzyme’s surface where the substrate molecule binds. The shape of the active site is complementary to the substrate, which explains why enzymes are specific.

活性位点是酶表面一个特殊形状的区域，底物分子在此结合。活性位点的形状与底物互补，这就解释了酶的特异性。

In the lock-and-key model, the substrate (key) fits perfectly into the active site (lock). This simple model helps us understand enzyme-substrate specificity in the Edexcel IGCSE course.

在锁钥模型中，底物（钥匙）完美契合活性位点（锁）。这个简单的模型有助于我们理解Edexcel IGCSE课程中的酶-底物特异性。

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3. Induced Fit Model: A More Accurate View | 诱导契合模型：更准确的观点

The induced-fit model is an updated version that states the active site is not a rigid shape; it changes shape slightly to allow the substrate to bind more tightly. This makes the enzyme more flexible and explains how some enzymes work on more than one similar substrate.

诱导契合模型是更新的版本，它认为活性位点不是刚性形状，而是会稍微改变形状以让底物更紧密地结合。这使得酶更加灵活，也解释了一些酶如何作用于多个相似底物。

After the reaction, the product is released, and the enzyme returns to its original shape, ready for another substrate molecule.

反应后，产物被释放，酶恢复其原有形状，准备与下一个底物分子结合。

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4. Reducing Activation Energy | 降低活化能

Every chemical reaction has an activation energy (Eₐ) – the minimum energy needed for the reaction to occur. Enzymes reduce this energy, making it easier for reactants to reach the transition state.

每个化学反应都有活化能（Eₐ）——即反应发生所需的最低能量。酶能降低这种能量，使反应物更容易达到过渡态。

By lowering Eₐ, enzymes can increase the rate of reaction by millions of times. The enzyme provides an alternative pathway with a lower energy barrier, but it does not change the overall energy change of the reaction.

通过降低活化能，酶可以使反应速率提高数百万倍。酶提供了一条能量屏障更低的替代途径，但不会改变反应的总能量变化。

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5. Effect of Temperature | 温度的影响

Temperature affects enzyme activity in two ways. As temperature rises from cold, particles gain kinetic energy and collide more often, so the rate of reaction increases. This continues until the optimum temperature is reached.

温度对酶活性有双重影响。当温度从低温升高时，粒子获得动能，碰撞更频繁，因此反应速率加快。这种趋势一直持续到达到最适温度。

For most human enzymes, the optimum is around 37°C. Beyond this, the enzyme begins to denature, and the rate rapidly falls to zero.

大多数人体酶的最适温度约为37°C。超过这个温度，酶开始变性，反应速率迅速下降直至为零。

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6. Effect of pH and Salt Concentration | pH和盐浓度的影响

Each enzyme has an optimum pH. 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 the enzyme’s active site, affecting substrate binding.

每种酶都有最适pH。例如，胃中的胃蛋白酶在pH 2时活性最高，而小肠中的胰蛋白酶在pH 8时活性最高。pH的变化会改变酶活性位点上的电荷，影响底物结合。

Extreme pH, too acidic or too alkaline, can break the bonds that hold the enzyme in shape, causing denaturation. Salt concentration has a similar effect; very high ionic strength disrupts hydrogen bonds and hydrophobic interactions.

极端的pH值，过酸或过碱，会破坏维持酶形状的键，导致变性。盐浓度也有类似影响；非常高的离子强度会破坏氢键和疏水相互作用。

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7. Substrate Concentration and Enzyme Concentration | 底物浓度和酶浓度

At a fixed enzyme concentration, increasing substrate concentration increases the rate of reaction up to a point. This is because more substrate molecules mean more collisions with active sites. Eventually, all active sites are occupied, and the rate reaches a plateau.

在酶浓度固定的情况下，增加底物浓度会在一定限度内提高反应速率。因为更多的底物分子意味着与活性位点的碰撞更多。最终，所有活性位点都被占据，速率达到平台期。

In contrast, increasing enzyme concentration (with excess substrate) increases the rate proportionally, because there are more active sites available. This relationship is important for understanding enzyme kinetics.

相反，在底物过量时增加酶浓度，速率会成比例增加，因为可用的活性位点更多了。这种关系对理解酶动力学很重要。

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8. Denaturation of Enzymes | 酶的变性

Denaturation is a permanent change in the enzyme’s three-dimensional shape, caused by high temperature or extreme pH. The active site is destroyed, so the substrate can no longer bind, and the enzyme loses its catalytic function.

变性是酶三维形状的永久性改变，由高温或极端pH引起。活性位点被破坏，底物无法再结合，酶失去催化功能。

Denaturation is irreversible in most cases because the bonds (like hydrogen bonds and disulfide bridges) that maintain the structure are broken. However, slow cooling from a slightly high temperature may sometimes allow recovery in some enzymes.

在大多数情况下，变性是不可逆的，因为维持结构的键（如氢键和二硫键）被破坏。然而，从略高的温度缓慢冷却有时可能使一些酶恢复活性。

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9. Competitive and Non-competitive Inhibitors | 竞争性和非竞争性抑制剂

Competitive inhibitors have a shape similar to the substrate, so they occupy the active site and block the real substrate. Their effect can be reduced by increasing substrate concentration.

竞争性抑制剂的形状与底物相似，因此它们占据活性位点并阻止真正的底物结合。增加底物浓度可以减轻其抑制作用。

Non-competitive inhibitors bind to a different site on the enzyme, changing the shape of the active site. Increasing substrate concentration cannot overcome this type of inhibition, because the enzyme’s structure is altered.

非竞争性抑制剂结合在酶的其他部位，改变活性位点的形状。增加底物浓度无法克服这种抑制，因为酶的结构已经改变。

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10. Biological Applications of Enzymes | 酶的生物学应用

Enzymes are vital in digestion: amylase, protease, and lipase break down carbohydrates, proteins, and lipids respectively. Each is secreted at optimal conditions to help the body absorb nutrients.

酶在消化中至关重要：淀粉酶、蛋白酶和脂肪酶分别分解碳水化合物、蛋白质和脂质。它们各自在最佳条件下分泌，帮助身体吸收营养。

Enzymes also play a role in DNA replication and transcription, where polymerase enzymes form new DNA strands. Without them, cell division would be impossible.

酶在DNA复制和转录中也发挥作用，聚合酶在此过程中形成新的DNA链。没有它们，细胞分裂就无法进行。

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11. Industrial and Medical Uses | 工业和医疗应用

Industrially, enzymes are used to make foods, medicines, and washing powders. For example, proteases in biological detergents break down protein stains, and isomerase is used to convert glucose into fructose for sweeteners.

在工业上，酶被用于制造食品、药物和洗衣粉。例如，生物洗衣粉中的蛋白酶分解蛋白质污渍，而异构酶用于将葡萄糖转化为果糖作为甜味剂。

Medical uses include lactose-free milk production and diagnostic tests like glucose sensors. Enzymes are also used in biosensors because of their high specificity.

医疗应用包括生产无乳糖牛奶以及葡萄糖传感器等诊断测试。由于酶的高特异性，它们也用于生物传感器中。

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12. Practical: Investigating the Effect of pH | 实验：探究pH的影响

A common IGCSE experiment uses amylase to hydrolyse starch at different pH values. Buffer solutions create varying pH environments, and iodine solution tests for starch presence every few seconds to measure the time until starch disappears.

一个常见的IGCSE实验使用淀粉酶在不同pH下水解淀粉。缓冲溶液创造不同pH环境，每隔几秒用碘液检测淀粉是否存在，以测定淀粉消失所需时间。

Typical results show a minimum time at the optimum pH and longer times or no breakdown at extreme pH. You should be able to plot a graph of rate against pH and describe the bell-shaped curve.

典型结果显示，在最佳pH下消失时间最短，而在极端pH下时间变长或淀粉不分解。你应该能够绘制速率对pH的曲线图，并描述钟形曲线。

Exam tip: When explaining pH results, refer to hydrogen ion concentration altering enzyme shape and denaturation at extremes.

考试提示：在解释pH结果时，要提到氢离子浓度改变酶形状以及极端条件下发生变性。

Published by TutorHao | Science Revision Series | aleveler.com

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