📚 Enzymes: Biological Catalysts | 酶：生物催化剂
Enzymes are biological catalysts that control almost every chemical reaction inside living cells. Without enzymes, reactions such as digestion and respiration would be far too slow to support life. This revision article explains the structure of enzymes, how they act, the factors that affect their activity, and their practical applications, in line with the Edexcel IGCSE Biology specification.
酶是控制活细胞内几乎一切化学反应的生物催化剂。没有酶，消化和呼吸等反应会慢到无法维持生命。本文系统讲解酶的结构、作用方式、影响酶活性的因素及其实际应用，完全符合 Edexcel IGCSE 生物考纲的要求。
1. What Are Enzymes? | 什么是酶？
Enzymes are proteins that speed up chemical reactions without being used up in the process. A substance that increases the rate of a reaction but remains chemically unchanged at the end is called a catalyst. Enzymes are therefore often described as biological catalysts.
酶是能加速化学反应的蛋白质，但自身在反应过程中不会被消耗。能够提高反应速率并最终保持化学性质不变的物质称为催化剂，因此酶常被称为生物催化剂。
Enzymes are globular proteins. Long chains of amino acids fold into a compact, roughly spherical shape. This shape is vital because it creates a special region called the active site, where the substrate binds. Because each enzyme has a unique three-dimensional structure, each enzyme is usually specific to one reaction or one type of substrate.
酶属于球状蛋白质。氨基酸长链折叠成致密、近似球形的结构。这种形状至关重要，因为它形成了一个称为活性位点的特殊区域，底物在这里结合。由于每种酶的立体结构独一无二，所以一种酶通常只专一催化一种反应或一类底物。
2. Active Site and Specificity | 活性位点与专一性
The active site is usually a small cleft or pocket on the surface of the enzyme. The shape of the active site is complementary to the shape of the substrate, the reactant on which the enzyme acts. Amino acid side chains around the active site form hydrogen bonds, ionic bonds and other weak interactions that hold the substrate in the correct position.
活性位点通常是酶表面的一个小裂缝或凹陷。活性位点的形状与底物（即酶作用的反应物）的形状互补。活性位
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