Peptides are short chains of amino acids linked by peptide bonds. Typically, peptides contain less than 50 amino acids. Anything longer is considered a protein.
Peptides serve many important biological functions. For example:
Some peptides act as chemical messengers and play roles in cell signaling, like hormones and neurotransmitters.
Other peptides have antimicrobial, antifungal, or antiviral properties that form part of the innate immune system.
Peptides are also involved in various cellular processes like blood clotting, nutrient transport, enzyme activation, etc.
There are several ways to classify peptides:
Size: Peptides can be categorized by length as dipeptides (2 amino acids), tripeptides (3 amino acids), tetrapeptides (4 amino acids), pentapeptides (5 amino acids), etc.
Function: Such as signaling peptides, antimicrobial peptides, cell-penetrating peptides, etc.
Structure: Linear, cyclic, branched peptides.
Some examples of important peptides include:
Oxytocin - a peptide hormone that stimulates uterine contractions during childbirth and milk let-down during breastfeeding
Glutathione - an antioxidant peptide that protects cells from oxidative damage
Bradykinin - a vasodilatory peptide that lowers blood pressure
How are peptides synthesized?
There are two main approaches:
Chemical peptide synthesis
The amino acids are sequentially coupled together on a solid resin support. Common methods are solid-phase peptide synthesis (SPPS) and solution-phase peptide synthesis.
Biosynthesis by cells or cell extracts
Cells can manufacture peptides by translating mRNA sequences and producing peptide chains via ribosomal synthesis.
Peptides can also be biosynthesized enzymatically in cell-free extracts.
In summary, peptides are short chains of amino acids that serve many key biological roles in cell signaling, immunity, catalysis, and more. Their small size yet vast diversity enables them to conduct precise interactions throughout the body. Advances in peptide synthesis methods continue to expand their therapeutic and commercial potential. Understanding the fundamentals of peptide structure and function provides insight into biological systems at the molecular level.