20種不同的有機分子結合起來組成多肽鏈或蛋白質。這20個氨基酸主結構相同，但每種又分別有各自不同的側基團。氨基酸的主要結構包括氨基（-NH2），羧基（-COOH）和中央碳原子，20個不同的側鏈（R基團）就結合在上面。R基團賦予氨基酸物理化學特性，例如極性（親水性和疏水性）以及電荷（酸性或正電荷，堿性或負電荷）。氨基酸連接起來形成多肽鏈，多肽鏈又折疊壓縮成球狀三維結構的功能蛋白。這種三維構造通過肽鏈上不同部位上的氨基酸連在一起，決定了蛋白活性。因此氨基酸序列和組成決定了蛋白的形狀和功能活性。

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.