Introduction to Peptides

What Are Peptides?

Peptides are short chains of amino acids linked by covalent amide bonds, typically ranging from 2 to approximately 50 amino acid residues in length. They occupy a unique position in biochemistry, bridging the gap between individual amino acids and larger proteins. While the boundary between peptides and proteins is not rigidly defined, most biochemists consider chains shorter than 50 residues to be peptides and longer chains to be proteins.

Amino Acids: The Building Blocks

Twenty standard amino acids serve as the monomeric units of peptide chains. Each amino acid contains an amino group (-NH2), a carboxyl group (-COOH), a hydrogen atom, and a distinctive side chain (R group), all bonded to a central alpha-carbon. The side chain determines each amino acid’s chemical properties, including charge, polarity, size, and reactivity.

When amino acids join together through condensation reactions, water is released and a peptide bond forms between the carboxyl group of one amino acid and the amino group of the next. This reaction is thermodynamically unfavorable under standard conditions, which is why biological systems and laboratory synthesis both require energy input or activation chemistry to drive bond formation.

Classification by Size

Peptides are commonly classified by the number of amino acid residues they contain:

• Dipeptides – Two amino acid residues (e.g., carnosine)
• Tripeptides – Three residues (e.g., glutathione, GHK)
• Oligopeptides – Typically 2-20 residues
• Polypeptides – Approximately 20-50 residues, though usage varies

Natural Occurrence and Function

Peptides are ubiquitous in biological systems. Endogenous peptides serve as hormones (insulin, oxytocin), neurotransmitters (enkephalins, substance P), antimicrobial agents (defensins, cathelicidins), and signaling molecules (cytokines, growth factors). The human body produces thousands of distinct peptides that regulate virtually every physiological process.

Many naturally occurring peptides are produced through enzymatic cleavage of larger precursor proteins. For example, insulin is initially synthesized as preproinsulin (110 amino acids), which is processed into proinsulin and then cleaved to yield the mature 51-amino-acid hormone.

Peptides in Modern Research

The study of peptides has expanded dramatically over the past three decades. Advances in solid-phase peptide synthesis (SPPS), analytical characterization techniques, and computational modeling have made it possible to design, synthesize, and evaluate peptides with unprecedented precision. Research peptides are used in studies spanning oncology, neuroscience, endocrinology, immunology, and metabolic disease.

As of 2024, over 80 peptide-based therapeutics have received regulatory approval worldwide, with more than 170 in active clinical trials and approximately 600 in preclinical development. This trajectory underscores the growing importance of peptide science in biomedical research.

Further Reading

• Peptide Bonds – Learn about the chemistry holding peptides together
• Peptides vs Proteins – Understand the key differences
• Peptide Synthesis – How research peptides are manufactured

For research use only. Not for human consumption. All products sold by Epiq Aminos are intended for laboratory research purposes only.