20种不同的有机分子结合起来组成多肽链或蛋白质。这20个氨基酸主结构相同，但每种又分别有各自不同的侧基团。氨基酸的主要结构包括氨基（-NH2），羧基（-COOH）和中央碳原子，20个不同的侧链（R基团）就结合在上面。R基团赋予氨基酸物理化学特性，例如极性（亲水性和疏水性）以及电荷（酸性或正电荷，碱性或负电荷）。氨基酸连接起来形成多肽链，多肽链又折叠压缩成球状三维结构的功能蛋白。这种三维构造通过肽链上不同部位上的氨基酸连在一起，决定了蛋白活性。因此氨基酸序列和组成决定了蛋白的形状和功能活性。

One of the 20 different organic molecules that are joined together to form a polypeptide chain or a protein The twenty amino acids share a common backbone, but each has a specific side-group. The backbone structure of an amino acid consists of an amino (-NH₂) group, a carboxylic acid (-COOH) group, and a central carbon atom (designated C-alpha), to which one of twenty different side chains (the R-group) is attached. The R-groups give the amino acids their physical-chemical characteristics such as polarity (hydrophobic or hydrophilic) and charge (acidic or positive versus basic or negative). The joining of the amino acids into a chain results in the formation of a polypeptide chain which then folds into the compact, globular three-dimensional structure that is a functional protein. This three-dimensional conformation is held together by the interactions of the amino acids at different parts of the polypeptide chain with each other, and determines the activity of the protein. Thus, the amino acid order and content determines the shape and functional activity of the protein.