Both peptide and protein are fundamental components of cells that carry out important biological functions. They are made up of strings of the body’s basic building blocks — amino acids — and held together by peptide bonds (also called amide bonds). However, peptides and proteins are still very different in structure, function and other factors.
Amino acid, Peptide and Protein
To identify the difference between peptides and proteins, we should firstly know something about amino acid. Biologically, different numbers of amino acids are linked in peptide bond order to form peptides or peptides of different lengths, called multiple peptides or polypeptide. A certain spatial structure formed by folding a polypeptide chain is a protein. Therefore, it’s widely known that, amino acid is the most basic substance that constitutes a biological protein and is related to life activities. It is the basic unit that constitutes a protein molecule in a living organism and has a very close relationship with the life activities of living things. There are 20 kinds of amino acids naturally present in proteins.
Peptide and Protein
The structural hierarchy of a protein can be abbreviated as: C, H, O, N and other elements → amino acid → polypeptide (peptide chain) → protein. So obviously we can see that peptides and proteins are in two different hierarchy levels, the mainly difference is as follows:
The basic distinguishes is structure. Peptides are smaller than proteins. Traditionally, peptides are defined as molecules that consist of between 2 and 50 amino acids, whereas proteins are made up of 50 or more amino acids. Let’s make it more specifically for some examples, Melanotan 2, abbreviation as MT2. From it’s full chemical sequence: Ac-Ser-Tyr-Ser-Nle-Glu-His-D-Phe-Arg-Trp-Gly-Lys-Pro-Val-NH2, we can know that MT2 has 13 amino acids, so MT2 is a peptide. We also call it a peptide hormone. Another peptide BPC-157, chemical formula: Gly-Glu-Pro-Pro-Pro-Gly-Lys-Pro-Ala-Asp-Asp-Ala-Gly-Leu-Val, with 15 amino acids, so apparently BPC-157 is also peptide.
In addition, peptides tend to be less well defined in structure than proteins, which can adopt complex conformations known as secondary, tertiary, and quaternary structures. A polypeptide is a subunit of a protein molecule. Some protein molecules have only one polypeptide chain, and some are composed of several polypeptide chains. A polypeptide is only the primary structural form of a protein, and a protein has a certain spatial structure. Protein is a combination of peptides and other substances. Simply put, a protein molecule can be composed of one peptide chain or a plurality of peptide chains connected by a certain chemical bond.
Peptides and proteins is also different in functional distinctions. Polypeptides are often biologically inactive and proteins are biologically active. Polypeptides are generally inactive ( for example, polypeptides produced by digestion of proteins in the stomach and small intestine), and with a very small number of active (such as vasopressin is a peptide hormone). Compared to proteins, polypeptides have a small molecular weight, no spatial structure, and are generally inactive. The protein has a large molecular weight, with a spatial structure, and is active. (the activity decreases or disappears after degeneration, and the activity disappears is called inactivation)