What are peptides?

Peptides are short chains of amino acids, which are the fundamental building blocks of proteins. Like proteins, peptides are composed of amino acids linked together by peptide bonds, but they differ primarily in size and complexity. Typically, peptides are defined as polymers consisting of between 2 and 100 amino acids; however, some scientific definitions consider peptides to contain no more than 50 amino acids. Once a chain exceeds this threshold, it is usually classified as a protein, though the dividing line can vary depending on the biological or biochemical context.

To visualize peptides, imagine a string of uniquely shaped beads—these beads represent the 20 standard (proteinogenic) amino acids that are universally encoded by the genetic code in humans and most other organisms. These amino acids can be linked in a vast array of sequences, each combination potentially resulting in a peptide with distinct biological functions or properties. The sequence and arrangement of these amino acids determine how the peptide folds, interacts with other molecules, and performs its specific biological role.

For instance, consider collagen, one of the most abundant and essential structural proteins in the body, providing strength and elasticity to skin, tendons, and cartilage. Collagen is characterized by a repeating tripeptide motif in which the amino acid glycine (Gly) appears at every third residue. The general pattern follows: …–Xaa–Yaa–Gly–…, where Xaa is often proline (Pro) and Yaa is frequently hydroxyproline. This repetitive sequence allows collagen to form a tight, triple-helical structure, contributing to its tensile strength and durability.

While peptides are often biologically active on their own—functioning as hormones, neurotransmitters, or signaling molecules—they can also act as precursors or fragments of larger proteins. Their versatility and targeted biological activity make peptides a focal point in biomedical research and therapeutic development, including in areas like regenerative medicine, metabolic disorders, and skin health.