Are proteins also peptides?


Peptide is a compound in which α-amino acids are linked together by peptide bonds, and it is also an intermediate product of protein hydrolysis.

Generally, the number of amino acids contained in the peptide is two to nine. According to the number of amino acids in the peptide, the peptide has various different names: a compound obtained by dehydration condensation of two amino acid molecules is called a dipeptide, and the analogy is analogous. Peptides, tetrapeptides, pentapeptides, etc., up to the nonapeptide. Compounds, usually dehydrated and condensed from 10 to 100 amino acids, are called polypeptides. They have a molecular weight of less than 10,000 Da (Dalton, Dalton) and are transparent to the semi-permeable membrane and are not precipitated by trichloroacetic acid and ammonium sulfate. There are also literatures that refer to peptides consisting of 2 to 10 amino acids as oligopeptides (small molecule peptides); peptides composed of 10 to 50 amino acids are called polypeptides; peptides composed of more than 50 amino acids are called proteins, in other words, Protein is sometimes referred to as a polypeptide. Polypeptide, also referred to as peptide, were discovered in the 20th century.


Protein is a substance having a certain spatial structure formed by twisting a polypeptide chain composed of an amino acid in an “dehydration condensation” manner. Proteins must contain carbon, hydrogen, oxygen, and nitrogen.

Protein is a polymer compound in which a-amino acids are combined in a certain order to form a polypeptide chain, and then one or more polypeptide chains are combined in a specific manner. Protein is the scaffold and main substance that constitutes the tissues and organs of the human body, and plays an important role in human life activities.

Amino acids are the basic building blocks of proteins. It is a substance that is closely linked to life and to various forms of life. Protein is involved in every cell and all important components in the body. Protein accounts for 16% to 20% of the body’s weight, that is, a 60kg adult has about 9.6~12kg of protein in the body. There are many kinds of proteins in the human body, and their properties and functions are different. However, they are composed of more than 20 kinds of amino acids (Amino acid) in different proportions, and are continuously metabolized and renewed in the body.


Proteins and peptides are basic components of cells and have important biological functions.Proteins, for example, shape cells and respond to signals from the extracellular environment.Certain peptides play a key role in regulating the activity of other molecules.Proteins and peptides are very similar in structure and consist of chains of amino acids joined together by peptide bonds (also known as amide bonds).So what’s the difference between a peptide and a protein?The basic differentiating factors are size and structure.Peptides are smaller than proteins.Traditionally, peptides have been defined as molecules of 2 to 50 amino acids, while proteins are composed of 50 or more amino acids.In addition, peptides are often less structurally defined than proteins, which may have complex conformations such as secondary, tertiary, and quaternary structures.There may also be functional differences between peptides and proteins.However, peptides can be subdivided into oligopeptides, which contain very few amino acids (e.g., 2 to 20), and polypeptides, which contain many amino acids.Proteins are formed by the joining together of one or more polypeptides.So proteins are essentially very large peptides.In fact, some researchers use the word peptide specifically to refer to oligopeptides, or relatively short chains of amino acids, while polypeptides are used to describe proteins, or chains of 50 or more amino acids.

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