📚 Enzymes and Their Role in Biological Reactions | 酶及其在生物反应中的作用
Enzymes are biological catalysts that speed up chemical reactions in living organisms without being used up themselves. They are essential for processes such as digestion, respiration, and photosynthesis.
酶是生物催化剂，能在不自身消耗的情况下加快生物体内的化学反应。它们对于消化、呼吸和光合作用等过程至关重要。
1. What Are Enzymes? | 什么是酶？
Enzymes are proteins made of long chains of amino acids folded into specific three-dimensional shapes. Each enzyme has a unique shape that determines its function.
酶是由氨基酸长链折叠成特定三维形状的蛋白质。每种酶都有决定其功能的独特形状。
- Enzymes are not changed permanently by the reactions they catalyse; they can be reused many times.
- 酶不会被其催化的反应永久改变；它们可以多次重复使用。
- Enzymes lower the activation energy of a reaction, making it happen faster at normal body temperatures.
- 酶降低了反应的活化能，使反应在正常体温下更快进行。
- Enzymes are specific – each enzyme catalyses only one type of reaction.
- 酶具有特异性——每种酶只催化一种类型的反应。
2. The Active Site and Specificity | 活性位点与特异性
The active site is a small region on the enzyme surface where substrate molecules bind. The shape of the active site is complementary to the substrate’s shape.
活性位点是酶表面的一个小区域，底物分子在此结合。活性位点的形状与底物的形状互补。
If the substrate does not fit the active site, no reaction occurs. This is why enzymes are highly specific – for example, amylase only breaks down starch, not proteins or fats.
如果底物不能匹配活性位点，反应就不会发生。这就是为什么酶具有高度特异性——例如，淀粉酶只分解淀粉，而不分解蛋白质或脂肪。
3. The Lock and Key Hypothesis | 锁钥假说
The lock and key hypothesis explains enzyme specificity. The enzyme is the lock, the substrate is the key. Only the correct key fits the lock.
锁钥假说解释了酶的特异性。酶是锁，底物是钥匙。只有正确的钥匙才能打开锁。
Enzyme + Substrate → Enzyme-Substrate Complex → Enzyme + Product
酶 + 底物 → 酶-底物复合物 → 酶 + 产物
During the reaction, the enzyme and substrate bind temporarily to form an enzyme-substrate complex. The reaction occurs, and the products are released, leaving the enzyme unchanged.
在反应过程中，酶和底物暂时结合形成酶-底物复合物。反应发生后，产物被释放，酶保持不变。
4. Effect of Temperature on Enzyme Activity | 温度对酶活性的影响
Temperature affects the rate of enzyme-controlled reactions. As temperature increases, molecules move faster and collide more often, so the rate increases.
温度影响酶促反应的速率。随着温度升高，分子运动加快，碰撞更频繁，因此速率增加。
| Temperature (°C) | Effect on Enzyme Activity |
| 0–40 | Rate increases steadily |
| Around 40 (optimum) | Maximum rate |
| Above 45–60 | Rate falls sharply; enzyme denatures |
At high temperatures, the enzyme’s bonds break and its shape changes irreversibly. This is called denaturation. The active site no longer fits the substrate, so the enzyme stops working.
在高温下，酶内部的键断裂，形状发生不可逆变化。这称为变性。活性位点不再匹配底物，因此酶停止工作。
5. Effect of pH on Enzyme Activity | pH对酶活性的影响
Each enzyme has an optimum pH. Most human enzymes work best at pH 7 (neutral), but pepsin in the stomach works best at pH 2.
每种酶都有最适pH。大多数人体酶在pH 7（中性）时活性最高，但胃中的胃蛋白酶在pH 2时活性最高。
Extreme pH values can denature enzymes by disrupting ionic bonds and hydrogen bonds, altering the active site’s shape. This is why maintaining a stable pH is important for organisms.
极端pH值会破坏离子键和氢键，改变活性位点形状，从而使酶变性。这就是为什么维持稳定的pH对生物体非常重要。
6. Enzyme Concentration and Substrate Concentration | 酶浓度与底物浓度
At a constant substrate concentration, increasing enzyme concentration increases the rate of reaction, because more active sites are available.
在底物浓度恒定时，增加酶浓度会提高反应速率，因为有更多的活性位点可用。
At a constant enzyme concentration, increasing substrate concentration increases the rate up to a point. After that, the rate levels off because all active sites are occupied.
在酶浓度恒定时，增加底物浓度在一定范围内会提高速率。之后速率趋于平稳，因为所有活性位点都被占用。
Rate ∝ [Enzyme] when substrate is in excess
当底物过量时，速率 ∝ [酶浓度]
Rate reaches V_max when enzyme sites are saturated
当酶位点饱和时，速率达到最大反应速度 V_max
7. Inhibitors | 抑制剂
Inhibitors are molecules that reduce or stop enzyme activity. They can be competitive or non-competitive.
抑制剂是降低或停止酶活性的分子。它们可分为竞争性抑制剂和非竞争性抑制剂。
- Competitive inhibitors have a similar shape to the substrate and block the active site. Their effect can be overcome by increasing substrate concentration.
- 竞争性抑制剂与底物形状相似，占据活性位点。增加底物浓度可克服其抑制作用。
- Non-competitive inhibitors bind elsewhere on the enzyme, changing its shape so the active site no longer works. Increasing substrate concentration does not help.
- 非竞争性抑制剂结合在酶的其他部位，改变酶的形状，使活性位点不再起作用。增加底物浓度无法克服。
Some inhibitors are irreversible, such as heavy metals or cyanide; they permanently destroy enzyme function.
一些抑制剂是不可逆的，如重金属或氰化物；它们会永久破坏酶的功能。
8. Uses of Enzymes in Industry and Medicine | 酶在工业和医药中的应用
Enzymes are widely used in biotechnology, food production, and medicine.
酶广泛应用于生物技术、食品生产和医药领域。
| Application | Enzyme(s) Used | Purpose |
| Biological detergents | Proteases, lipases | Break down protein and fat stains |
| Food industry | Amylase, glucose isomerase | Convert starch into sugars and syrups |
| Medicine | Streptokinase | Dissolve blood clots |
Enzymes are also used in diagnosing diseases, such as glucose sensors for diabetes, and in genetic engineering to cut and paste DNA.
酶也用于疾病诊断，例如糖尿病的血糖传感器，以及在基因工程中剪切和拼接DNA。
Published by TutorHao | Science Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
屏轩国际教育cambridge primary/secondary checkpoint, cat4, ukiset,ukcat,igcse,alevel,PAT,STEP,MAT, ibdp,ap,ssat,sat,sat2课程辅导，国外大学本科硕士研究生博士课程论文辅导