Peptides are naturally occurring biological molecules. Peptides are found in all living organisms and play a key role in all manner of biological activity. Like proteins, peptides are formed (synthesized) naturally from transcription of a sequence of the genetic code, DNA. Transcription is the biological process of copying a specific DNA gene sequence into a messenger molecule, mRNA, which then carries the code for a given peptide or protein. Reading from the mRNA, a chain of amino acids is joined together by peptide bonds to form a single molecule.
There are 20 naturally-occurring amino acids and, like letters into words, they can be combined into an immense variety of different molecules. When a molecule consists of 2-50 amino acids it is called a peptide, whereas a larger chain of > 50 amino acids generally is referred to as a protein. 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.
Peptides primarily creates a biological effect by binding to cell surface receptors:
For a peptide to exert its effect, it needs to bind to a receptor specific for that peptide and which is located in the membrane of relevant cells. A receptor penetrates the cell membrane and consists of an extracellular domain where the peptide binds, and an intracellular domain through which the peptide exerts its function upon binding and activation of the receptor. An example is the GLP-1 receptor, which is located on beta cells in the pancreas. Upon activation of the receptor by natural GLP-1 or a peptide analog (a synthesized molecule mimicking the effect of natural GLP-1, such as our lixisenatide), the cell is stimulated through a series of biological events to release insulin.
Peptides in Foods:
Peptides are naturally present in foodstuffs. Most simple peptides are the result of partial hydrolysis of protein polypeptide chains. On the other hand, nonprotein peptides have also been recorded in foods. Such peptides usually differ in structure from the peptides derived from proteins, and these structural variations may protect them from the action of peptidases.
Peptides may also be present in foods because they have been used as additives (e.g., sweeteners, flavor enhancers, or bulking agents for light beverages) to improve food quality. Some peptides produced by the enzymatic hydrolysis of proteins possess better functional properties than the parent proteins and consequently are used by the food industry for a variety of purposes.
Peptides have lower molecular weight and less secondary structures, as well as higher number of ionizable groups and exposure of hydrophobic groups than native proteins. These facts imply that solubility, surface activity, foaming, and emulsifying properties may be different from that of the intact protein.
Are peptides overhyped?
The term peptide has been over-generalised to a degree. There are specific roles of peptides and some are more active and successful than others. As with all ingredients, including retinol and vitamin C, there are different qualities of peptides. And as science evolves, so does the quality of peptides, so watch this space.
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