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What are peptides

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.

In the human body, peptides are found in every cell and tissue and perform a wide range of essential functions. Maintenance of appropriate concentration and activity levels of peptides is necessary to achieve homeostasis and maintain health.

The function that a peptide carries out is dependent on the types of amino acids involved in the chain and their sequence, as well as the specific shape of the peptide. Peptides often act as hormones and thus constitute biologic messengers carrying information from one tissue through the blood to another. Two common classes of hormones are peptide and steroid hormones. Peptide hormones are produced in glands, and a number of other tissues including the stomach, the intestine and the brain. Examples of peptide hormones are those involved in blood glucose regulation, including insulin, glucagon-like-peptide 1 (GLP-1) and glucagon, and those regulating appetite, including ghrelin.

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 analogue (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.