Enzymes: How They Work and Factors Affecting Them | 酶：工作原理与影响因素

📚 Enzymes: How They Work and Factors Affecting Them | 酶：工作原理与影响因素

Enzymes are biological catalysts that speed up chemical reactions inside living organisms without being used up themselves. They are essential for processes such as digestion, respiration, and photosynthesis. Understanding how enzymes work and what affects their activity is a core topic in IGCSE Science and appears frequently in Edexcel exams.

酶是生物催化剂，能在不消耗自身的前提下加速生物体内的化学反应。它们对消化、呼吸、光合作用等过程至关重要。理解酶的工作原理以及影响其活性的因素，是 IGCSE 科学的核心考点，也经常出现在 Edexcel 考试中。

1. What Are Enzymes? | 什么是酶？

Enzymes are proteins made up of long chains of amino acids folded into specific three-dimensional shapes. Each enzyme is highly specific and only catalyses one type of reaction or acts on one type of substrate. Without enzymes, many chemical reactions would occur too slowly to sustain life.

酶是由氨基酸长链折叠成特定三维形状的蛋白质。每种酶都具有高度专一性，只催化某一类反应或只作用于某一类底物。如果没有酶，许多化学反应就会慢得无法维持生命。

Enzymes remain unchanged after a reaction, so they can be reused.
They lower the activation energy needed for reactions.

酶在反应后保持不变，因此可以重复使用。
它们降低了反应所需的活化能。

2. Enzyme Structure and Active Site | 酶的结构与活性位点

The structure of an enzyme includes a region called the active site. The active site has a specific shape that fits the substrate molecule. The rest of the enzyme helps maintain this shape. Any change in temperature or pH can alter the shape of the active site and affect enzyme activity.

酶的结构中包含一个称为活性位点的区域。活性位点具有与底物分子匹配的特定形状。酶的其余部分帮助维持这一形状。温度或 pH 的任何变化都可能改变活性位点的形状，从而影响酶活性。

Term	Meaning
Substrate	The molecule that binds to the active site
Product	The molecule(s) formed after the reaction
Active site	The region where the substrate binds and reacts

术语	含义
底物	与活性位点结合的分子
产物	反应后生成的分子
活性位点	底物结合并发生反应的区域

3. The Lock-and-Key Model | 锁钥模型

The classic model used to explain enzyme specificity is the lock-and-key model. In this model, the active site is the ‘lock’ and the substrate is the ‘key’. Only the correctly shaped substrate can fit into the active site, just as only the correct key can open a lock. Once bound, the enzyme catalyses the conversion of substrate to product.

解释酶专一性的经典模型是锁钥模型。在该模型中，活性位点如同 ‘锁’，底物如同 ‘钥匙’。只有形状匹配的底物才能进入活性位点，就像只有正确的钥匙才能打开锁一样。一旦结合，酶便催化底物转化为产物。

Another model, called the induced-fit model, suggests that the active site changes shape slightly to accommodate the substrate. However, the lock-and-key model is sufficient for most IGCSE explanations.

另一种称为诱导契合模型的模型认为，活性位点会发生轻微形变以容纳底物。但对于 IGCSE 考试，锁钥模型通常足够。

4. Catalysis and Activation Energy | 催化与活化能

For a chemical reaction to begin, a certain amount of energy is needed; this is called the activation energy. Enzymes provide an alternative pathway with a lower activation energy. This means that more molecules have enough energy to react, so the reaction proceeds much faster.

化学反应开始时需要一定能量，这称为活化能。酶提供了一条活化能较低的替代途径。这意味着更多分子拥有足够的能量发生反应，因此反应速度大大加快。

Enzyme effect: substrates → products (rate increased by lowering activation energy)

酶的作用：底物 → 产物（通过降低活化能提高反应速率）

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

As temperature increases from cold, molecules move faster and collide more often, so enzyme activity increases. The rate of reaction doubles roughly for every 10 °C rise, up to an optimum temperature. For human enzymes, the optimum is usually about 37 °C. Above the optimum, the enzyme begins to lose its shape and becomes denatured.

当温度从低温升高时，分子运动加快，碰撞更频繁，因此酶活性增加。在达到最适温度之前，温度每升高 10 °C，反应速率大约翻倍。人体酶的最适温度通常约为 37 °C。超过最适温度后，酶开始变形并失活（变性）。

At low temperatures, enzymes are inactive but still functional.
At high temperatures, the active site changes permanently.
Denaturation is usually irreversible.

低温时，酶活性较低但仍能发挥功能。
高温时，活性位点发生永久性改变。
变性通常是不可逆的。

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

Each enzyme has an optimum pH at which it works best. For example, pepsin in the stomach works best at pH 2, while amylase in the mouth and pancreas works best at pH 7. Changes in pH affect the bonding and shape of the enzyme. Extreme pH values can cause denaturation by disrupting hydrogen bonds and other interactions.

每种酶都有其作用最佳的最适 pH。例如，胃中的胃蛋白酶最适 pH 约为 2，而口腔和胰腺中的淀粉酶最适 pH 约为 7。pH 的变化会影响酶的化学键和形状。极端 pH 会破坏氢键和其他相互作用，从而导致酶变性。

pH too high or too low → active site shape changes → enzyme denatures

pH 过高或过低 → 活性位点形状改变 → 酶变性

7. Substrate Concentration | 底物浓度

At a fixed enzyme concentration, increasing the substrate concentration will increase the rate of reaction, because more substrate molecules are available to collide with active sites. However, once all active sites are occupied, the rate reaches a maximum and adding more substrate has no further effect. The enzyme has become saturated.

在酶浓度固定的情况下，增加底物浓度会提高反应速率，因为更多底物分子可与活性位点碰撞。然而，一旦所有活性位点都被占据，反应速率达到最大值，此时再增加底物也不会加快反应。酶已达到饱和状态。

Linear increase at low substrate concentrations.
Plateau at high substrate concentrations.

低底物浓度时速率线性上升。
高底物浓度时速率达到平台。

8. Enzyme Concentration | 酶浓度

If substrate is present in excess, increasing the enzyme concentration increases the rate of reaction linearly. More enzymes mean more available active sites, so more substrate can be converted to product in the same time. There is no saturation limit as long as substrate is not limiting.

如果底物过量，增加酶浓度会使反应速率线性增加。更多酶意味着有更多活性位点可用，因此在相同时间内可以转化更多底物。只要底物不成为限制因素，就不会出现酶饱和上限。

In practice, very high enzyme concentrations may become limited by other factors such as product accumulation or insufficient mixing.

在实际中，非常高的酶浓度可能会受到产物积累或混合不均等其他因素的限制。

9. Inhibitors | 抑制剂

Substances that reduce enzyme activity are called inhibitors. Competitive inhibitors have a similar shape to the substrate and compete with it for the active site. Non-competitive inhibitors bind away from the active site and change the enzyme’s shape, making the active site less effective. Some inhibitors are reversible, while others are irreversible.

降低酶活性的物质称为抑制剂。竞争性抑制剂与底物形状相似，并与底物竞争活性位点。非竞争性抑制剂则结合在活性位点以外的位置，改变酶的形状，使活性位点效率降低。有些抑制剂是可逆的，有些是不可逆的。

Type	Effect	Overcome by more substrate?
Competitive	Blocks active site	Yes
Non-competitive	Changes enzyme shape	No

类型	作用	增加底物能否缓解？
竞争性	占据活性位点	能
非竞争性	改变酶的形状	不能

10. Applications of Enzymes in Industry and Medicine | 酶在工业与医学中的应用

Enzymes are widely used commercially because they are specific and work under mild conditions. Biological washing powders contain proteases and lipases to break down protein and fat stains. In medicine, enzymes are used to diagnose diseases, clean wounds, and even in some treatments. In food production, enzymes help convert starch into sugar, and yeast enzymes are used for fermentation.

酶因其专一性和温和的工作条件而广泛应用于商业领域。加酶洗衣粉中含有蛋白酶和脂肪酶，用于分解蛋白质和脂肪污渍。在医学中，酶可用于疾病诊断、清洁伤口，甚至用于某些治疗。在食品生产中，酶帮助将淀粉转化为糖，而酵母中的酶则用于发酵。

Protease in washing powder breaks down protein stains.
Amylase is used to convert starch to sugar in syrups.
Glucose oxidase is used in blood glucose sensors.

洗衣粉中的蛋白酶可分解蛋白质污渍。
淀粉酶用于将淀粉转化为糖浆中的糖。
葡萄糖氧化酶用于血糖传感器。

11. Practical Skills: Measuring Enzyme Activity | 实验技能：测量酶活性

In IGCSE practical work, enzyme activity can be measured by observing the rate of product formation or substrate disappearance. For example, amylase breaks down starch to maltose; adding iodine solution will show a colour change from blue-black to brown when starch is no longer present. Catalase activity can be measured by the volume of oxygen gas produced over time.

在 IGCSE 实验操作中，酶活性可通过观察产物生成速率或底物消耗速率来测量。例如，淀粉酶将淀粉分解为麦芽糖；加入碘液后，当淀粉不再存在时，颜色会从蓝黑色变为棕色。过氧化氢酶活性可通过收集单位时间内产生的氧气体积来衡量。

To find the optimum temperature or pH, repeat the experiment at different conditions and plot the rate against the variable. The peak of the graph gives the optimum value.

若要找出最适温度或 pH，可在不同条件下重复实验，并以速率为纵轴、变量为横轴作图。曲线最高点即为最适值。

12. Conclusion | 结论

Enzymes are vital catalysts with specific active sites that lower activation energy. Their activity is affected by temperature, pH, and concentrations of substrate and enzyme. Understanding the factors that affect enzymes allows us to control reactions usefully in industry, medicine, and everyday life. In Edexcel IGCSE Science, make sure you can describe the lock-and-key model, interpret graphs of enzyme activity, and explain denaturation.

酶是重要的催化剂，具有特定的活性位点并能降低活化能。其活性受温度、pH、底物浓度和酶浓度的影响。理解影响酶活性的因素，有助于我们在工业、医学和日常生活中有效控制反应。在 Edexcel IGCSE 科学考试中，请务必能够描述锁钥模型、解读酶活性曲线并解释变性过程。

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Enzymes: How They Work and Factors Affecting Them | 酶：工作原理与影响因素