A-Level Biology: Proteins – Exam Essentials | A-Level 生物：蛋白质 考点精讲

📚 A-Level Biology: Proteins – Exam Essentials | A-Level 生物：蛋白质 考点精讲

Proteins are one of the most diverse and essential macromolecules in living organisms. In A-Level Biology, mastering their structure – from amino acid sequence to functional quaternary assemblies – is fundamental to understanding processes such as enzyme action, cell signalling, and molecular transport.

蛋白质是生物体中最具多样性且必不可少的大分子之一。在A-Level生物中，掌握蛋白质的结构——从氨基酸序列到功能性四级组装——是理解酶作用、细胞信号传导和分子运输等过程的基础。

1. Amino Acids: The Building Blocks | 氨基酸：构成蛋白质的基本单位

All proteins are polymers of amino acid monomers. A typical amino acid has a central α-carbon bonded to an amino group (–NH₂), a carboxyl group (–COOH), a hydrogen atom, and a variable R group (side chain).

所有蛋白质都是由氨基酸单体组成的聚合物。一个典型的氨基酸含有中央α-碳原子，分别连接着氨基 (–NH₂)、羧基 (–COOH)、氢原子和可变的R基团（侧链）。

There are 20 standard amino acids, each with a unique R group that determines its chemical properties – non-polar, polar uncharged, acidic (negatively charged), or basic (positively charged). Glycine is the simplest amino acid, with R = H.

共有20种标准氨基酸，每种都具有独特的R基团，决定了其化学性质——非极性、极性不带电、酸性（带负电）或碱性（带正电）。甘氨酸是最简单的氨基酸，其R基团为氢原子。

Essential amino acids cannot be synthesised by the human body and must be obtained from the diet.

必需氨基酸是人体无法合成、必须从饮食中摄取的氨基酸。

2. Peptide Bonds and Condensation | 肽键与缩合反应

Amino acids are linked by condensation reactions. The carboxyl group of one

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