📚 Enzymes: The Biological Catalysts | 酶：生物催化剂
Enzymes are proteins that act as biological catalysts, dramatically speeding up chemical reactions inside cells. They are vital for life, enabling processes such as digestion, respiration, and photosynthesis to occur at rates that sustain living organisms. This article covers the structure, function, and real-world applications of enzymes for the Edexcel IGCSE Biology syllabus.
酶是作为生物催化剂的蛋白质，能极大地加快细胞内的化学反应。它们对生命至关重要，使消化、呼吸和光合作用等过程能够以维持生命所需的速度发生。本文面向 Edexcel IGCSE 生物课程，系统讲解酶的结构、功能及实际应用。
1. What Are Enzymes? | 什么是酶？
Enzymes are globular proteins made from chains of amino acids. Each enzyme has a specific three-dimensional shape, which is essential for its function. The unique shape comes from the way the amino acid chain folds, held together by bonds such as hydrogen bonds and disulfide bridges.
酶是由氨基酸链组成的球状蛋白质。每一种酶都有特定的三维结构，这对它的功能至关重要。这种独特的形状来自氨基酸链的折叠方式，由氢键和二硫键等化学键维持。
Enzymes are not used up during a reaction; they can be used repeatedly. In a reaction, the enzyme binds to a reactant called the substrate, lowers the activation energy needed, and converts it into product(s).
酶在反应过程中不会被消耗，可以反复使用。在反应中，酶与称为底物的反应物结合，降低所需的活化能，并将其转化为产物。
2. The Active Site and Specificity | 活性位点与特异性
Each enzyme has an active site – a region with a specific shape that fits only one particular substrate (or a small group of substrates). This is why enzymes are specific: the enzyme amylase only breaks down starch, while lipase only breaks down fats.
每种酶都有一个活性位点——一个具有特定形状的区域，只能匹配一种特定底物（或一小类底物）。这就是酶具有特异性的原因：淀粉酶只分解淀粉，而脂肪酶只分解脂肪。
The substrate molecule binds to the active site to form an enzyme-substrate complex. If the substrate shape does not match, it cannot bind, and no reaction occurs. This specificity is often compared to a key fitting into a lock.
底物分子与活性位点结合形成酶-底物复合物。如果底物形状不匹配，就无法结合，反应便不会发生。这种特异性常被比作钥匙插入锁孔。
3. Lock and Key vs Induced Fit | 锁钥模型与诱导契合模型
Two models explain how enzymes bind to substrates. The lock and key model suggests that the active site is rigid, and only an exactly matching substrate can bind. This simple model explains enzyme specificity but does not account for all observations.
有两种模型解释酶与底物的结合方式。锁钥模型认为活性位点是刚性的，只有完全匹配的底物才能结合。这个简单模型解释了酶的特异性，但无法解释所有观察现象。
The induced fit model is more accurate: the active site is flexible, and when the substrate binds, the shape of the active site changes slightly to achieve a perfect fit. This stresses the enzyme molecule and lowers the activation energy further, increasing reaction speed.
诱导契合模型更为准确：活性位点是柔性的，当底物结合时，活性位点的形状会发生轻微改变，达到完美匹配。这会拉伸酶分子，进一步降低活化能，提高反应速度。
4. Factors Affecting Enzyme Activity: Temperature | 影响酶活性的因素：温度
Temperature affects the rate of enzyme-controlled reactions. As temperature rises, particles gain kinetic energy, so enzyme-substrate complexes form more frequently. The rate approximately doubles for every 10 °C rise, up to the optimum temperature.
温度影响酶促反应速率。随着温度升高，粒子获得更多动能，酶-底物复合物形成得更频繁。温度每升高 10 °C，反应速率大约翻一倍，直到达到最适温度。
For most human enzymes, the optimum temperature is about 37 °C. Above this, the enzyme's structure begins to vibrate and bonds break. The active site changes shape and can no longer bind the substrate; the enzyme is denatured. Denaturation is permanent.
大多数人体酶的最适温度约为 37 °C。超过此温度，酶的结构会剧烈振动，化学键开始断裂。活性位点改变形状，无法再与底物结合；酶发生变性。变性是不可逆的。
on rate → Temperature graph: rate rises to optimum, then falls sharply after denaturation.
反应速率 → 温度曲线：速率升至最适点，变性后骤降。
5. Factors Affecting Enzyme Activity: pH | 影响酶活性的因素：pH
Enzymes also have an optimum pH. Most enzymes in the human body work best at pH 7 (neutral), but stomach enzymes like pepsin work best at pH 2, which is highly acidic. The pH affects the charges on the amino acids and the hydrogen bonds that hold the enzyme's shape.
酶也有最适 pH。人体内大多数酶在 pH 7（中性）时活性最高，但胃蛋白酶等胃部酶在 pH 2 的强酸环境中活性最高。pH 影响氨基酸上的电荷和维持酶形状的氢键。
If the pH is too high or too low, the bonds within the enzyme break, changing the shape of the active site. This means the substrate cannot fit, and the enzyme becomes denatured. Thus, each enzyme functions only within a narrow pH range.
如果 pH 过高或过低，酶内部的化学键会断裂，改变活性位点的形状。这导致底物无法结合，酶发生变性。因此，每种酶只能在很窄的 pH 范围内发挥作用。
6. Enzyme Concentration and Substrate Concentration | 酶浓度与底物浓度
Increasing enzyme concentration increases the rate of reaction, as long as substrate is available. More enzyme molecules mean more active sites, so more enzyme-substrate complexes can form per second.
只要底物充足，增加酶浓度会提高反应速率。更多的酶分子意味着更多的活性位点，因此每秒能形成更多酶-底物复合物。
Increasing substrate concentration also increases the rate until a saturation point. At saturation, all active sites are occupied, and further addition of substrate has no effect, because the enzyme is working at its maximum rate. Adding more enzyme at this point will increase the rate again.
增加底物浓度也会提高反应速率，直到饱和点。达到饱和时，所有活性位点均被占满，再增加底物也不会改变速率，因为酶已经以最大速率工作。此时增加酶浓度则会再次提高速率。
Substrate concentration → Rate: increases then plateaus.
底物浓度 → 反应速率：先上升后趋于平稳。
7. Inhibitors | 抑制剂
Inhibitors are substances that slow down or stop enzyme activity. Competitive inhibitors have a shape similar to the substrate and compete for the active site. If they bind, the substrate cannot bind. Their effect can be reduced by adding more substrate.
抑制剂是使酶活性降低或停止的物质。竞争性抑制剂具有与底物相似的形状，与底物竞争活性位点。一旦结合，底物就无法结合。其抑制作用可以通过增加底物浓度来减轻。
Non-competitive inhibitors bind to a site other than the active site, changing the enzyme's shape so that the active site no longer works. Adding more substrate does not help. Some inhibitors are reversible, others are irreversible; heavy metals like lead and mercury are powerful non-competitive inhibitors.
非竞争性抑制剂结合在活性位点以外的位置，改变酶的整体形状，使活性位点失效。增加底物浓度也无济于事。有些抑制剂是可逆的，有些是不可逆的；铅和汞等重金属是强效的非竞争性抑制剂。
8. Enzymes in Digestion | 酶在消化中的作用
The digestive system uses enzymes to break down large food molecules into small, soluble molecules that can be absorbed. Amylase breaks starch into maltose, produced in the salivary glands and pancreas. Proteases such as pepsin break proteins into amino acids in the stomach and small intestine. Lipase breaks fats into fatty acids and glycerol in the small intestine.
消化系统利用酶将大分子食物分解成可吸收的小分子可溶性物质。淀粉酶将淀粉分解为麦芽糖，由唾液腺和胰腺分泌。胃和小肠中的胃蛋白酶等蛋白酶将蛋白质分解为氨基酸。小肠中的脂肪酶将脂肪分解为脂肪酸和甘油。
Bile is not an enzyme, but it emulsifies fats, increasing the surface area for lipase to work on. The small intestine has a very high pH, which is optimal for pancreatic enzymes, and the stomach has a very low pH, optimal for pepsin.
胆汁不是酶，但它能将脂肪乳化，增大脂肪酶作用的表面积。小肠内 pH 较高，适合胰酶发挥作用；胃内 pH 很低，适合胃蛋白酶发挥作用。
9. Enzymes in Industry and Medicine | 酶在工业和医学中的应用
Enzymes are widely used in manufacturing and medicine. In biological washing powders, lipases and proteases remove fat and protein stains at temperatures lower than traditional laundering, saving energy. In food production, enzymes are used to make cheese, bread, and fruit juice.
酶广泛用于制造业和医学。在生物洗衣粉中，脂肪酶和蛋白酶能在低于传统洗涤的温度下去除油渍和蛋白质污渍，节约能源。在食品生产中，酶被用于制作奶酪、面包和果汁。
In medicine, enzymes are used in diagnostic tests and treatments. For example, glucose oxidase is used in test strips for people with diabetes, and lactase supplements help people who are lactose intolerant digest dairy products. Scientists also use enzymes to cut and modify DNA in genetic engineering.
在医学上，酶用于诊断测试和治疗。例如，葡萄糖氧化酶用于糖尿病患者的试纸条，乳糖酶补充剂帮助乳糖不耐受人群消化乳制品。科学家还利用酶在基因工程中切割和修饰 DNA。
10. The Importance of Enzymes | 酶的重要性
Enzymes control virtually every metabolic reaction in living cells, from cellular respiration to DNA replication. Without enzymes, reactions would require extreme temperatures or strong chemicals, which would destroy cells. Their specificity and efficiency make them indispensable for life.
酶控制着活细胞中几乎所有的代谢反应，从细胞呼吸到 DNA 复制。没有酶，反应将需要极高的温度或强化学试剂，这会破坏细胞。酶的特异性和高效性使其成为生命不可或缺的物质。
Understanding enzymes also helps us develop medicines, industrial processes, and agricultural products. From answering exam questions on denaturation to explaining why we digest food, enzymes remain a cornerstone of biology and a key topic for IGCSE success.
理解酶还有助于我们开发药物、改进工业流程和农业产品。从回答关于变性的考题，到解释我们为何能消化食物，酶始终是生物学的基石，也是 IGCSE 考试的关键主题。
Published by TutorHao | Biology Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
或截图后用「扫一扫 → 相册」选择本图