protein, peptide, amino acid 有咩關係?

Notes on terminology

A polypeptide is a single linear chain of amino acids. 幾多粒都算
A protein are one or more polypeptides more than about 50 amino acids long.
An oligopeptide or (simply) a peptide is a polypeptide less than 30-50 amino acids long.
A dipeptide has two amino acids.
A tripeptide has three amino acids.
A pentapeptide has five amino acids.
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polypeptide 只係一條長長的 peptide chain 而無立體結構.
protein 可以由一條或多條polypeptide 組成, 每條polypeptide 可以有自己既立體結構, 由disulphide bond 連結貼好, 例如有d位打個髮夾圈[loop] 或成螺旋形[spiral]. polypeptide 之間又有bond 連結貼好, 形成一個大分子.
protein 的例子: 血紅素haemoglobin 係由4條polypeptide 串在一起, 中間加1個含鐵離子的 haeme group.

Protein>Peptide>Amino Acid

amino acid is the basic unit of a protein.
dipeptide is the product of the condesation (縮合作用) between 2 amino acid, in the other words,dipeptide is a peptidechain which contain just 2 amino acid.But polypeptide is a peptidechain which contain more than2amino acid.
generally, protein can be divided into 3 structure: primary,secondary, tertiary structure.
we know that there are several kinds of bonding between different polypeptides or a same polypeptide,includind 1.hydrogen bond 2.disulfide bond 3.ionic bond 4.hydrophobic interaction.these bonding can make polypeptide bend and have a specific shape(active site). therefore, the different between polypeptide and protein is protein can have a biotic function (because it have active site(s))

protein係蛋白質, 係一個由chains 組成的
peptide係組成protein的chains
amino acid 係組成peptide的基本單位