What are peptides? Peptides are short chains of amino acids that are linked by a chemical bond called the peptide bond. Most peptides contain between 2 and about 50 amino acids. The body produces thousands of them, for example as hormones and signalling molecules, and chemists can make the same or modified sequences in the laboratory. This guide explains how peptides are built, how they differ from proteins, how synthetic research peptides are made and tested, and in which research areas they are used.
What are peptides? A short definition
A peptide is a molecule made of amino acids in a fixed order. This order is called the sequence. The sequence decides the shape of the peptide, and the shape decides which receptors or other molecules the peptide can bind to. Two peptides with the same amino acids in a different order are two different compounds.
Scientists name peptides by their length. The names come from Greek number words:
Dipeptide: 2 amino acids
Tripeptide: 3 amino acids, for example glutathione
Tetrapeptide: 4 amino acids, for example Epitalon (Ala-Glu-Asp-Gly)
Pentadecapeptide: 15 amino acids, for example BPC-157
Oligopeptide and polypeptide: general terms for short and longer chains
How peptides are built: amino acids and the peptide bond
Amino acids are the building blocks of all peptides. Each amino acid has an amino group (–NH2), a carboxyl group (–COOH) and a side chain. The side chain is different for each amino acid. It makes an amino acid water-loving or water-repelling, charged or neutral. Living organisms use 20 standard amino acids. Laboratories can also use modified amino acids that do not occur in nature.
A peptide bond forms when the carboxyl group of one amino acid reacts with the amino group of the next one. One molecule of water is released in this reaction. Chemists call this a condensation reaction, and the bond is an amide bond. The chain therefore has two different ends: the N-terminus with a free amino group and the C-terminus with a free carboxyl group. Sequences are always written from the N-terminus to the C-terminus.
Because the side chains differ, peptides of the same length can behave very differently. Some dissolve easily in water, others need a different solvent. Some are stable for years as dry powder, others are sensitive to oxidation. These properties matter later, when peptides are stored and handled in the laboratory.
Peptides vs proteins: where the line is
Peptides and proteins are built in the same way. Both are chains of amino acids joined by peptide bonds. The difference is mainly size and structure. A common rule of thumb places the line at about 50 amino acids: shorter chains are peptides, longer chains are proteins. The rule is not strict. Insulin has 51 amino acids and is often called a peptide hormone.
The more important difference is the three-dimensional shape. A protein folds into a stable structure with several levels of organisation, and often several chains work together. Most peptides are more flexible. Many have no fixed shape until they bind to their target. This is one reason why researchers can synthesise and modify peptides much more easily than whole proteins.
Natural and synthetic peptides in research
Natural peptides are produced by living organisms. Examples are hormones such as oxytocin and glucagon, the incretin hormones GLP-1 and GIP from the gut, and antimicrobial peptides of the immune system. Many fragments of larger proteins are also active as peptides.
Synthetic peptides are made by chemical synthesis. They fall into three groups. Some copy a natural sequence exactly. Some are fragments of a larger protein, such as TB-500, which is based on a segment of the protein thymosin beta-4. Others are analogues: the sequence is changed on purpose, for example with a fatty acid side chain that makes the molecule more stable. Semaglutide is such an analogue of human GLP-1. The research peptide BPC-157 is a synthetic 15-amino-acid sequence that was derived from a protein in gastric juice.
Peptides are also an established class of medicines. According to a review by Muttenthaler and colleagues in Nature Reviews Drug Discovery (2021), more than 80 peptide drugs have reached the market since the introduction of insulin. Research peptides sold for laboratory work are a different category. They are research chemicals, not approved medicines, even when the sequence is the same.
How research peptides are made: synthesis and lyophilisation
Almost all research peptides are made by solid-phase peptide synthesis, or SPPS. Robert Bruce Merrifield described the method in 1963 and received the Nobel Prize in Chemistry in 1984 for it. The principle is simple. The first amino acid is attached to a small resin bead. The chemist then adds one amino acid after the other. Protecting groups block the reactive parts of each amino acid so that only the intended bond forms. After each step, a wash removes the excess reagents.
When the full sequence is complete, the peptide is cut from the resin and the protecting groups are removed. The crude product still contains shorter sequences and by-products. Preparative HPLC (high-performance liquid chromatography) separates the target peptide from these impurities.
The purified peptide is then lyophilised. Lyophilisation means freeze-drying: the solution is frozen and the water is removed under vacuum. The result is a white, dry powder. Without water, most degradation reactions of peptides stop or slow down strongly. For this reason research peptides are supplied as lyophilised powder in sealed glass vials. Our guide on freeze-thaw cycles and peptide stability explains why the powder is robust and the solution is not.
How the quality of research peptides is documented
A label states which peptide should be in a vial. Only an analysis shows what is in the vial. The standard document for this is the certificate of analysis, or COA. For research peptides it usually reports two tests:
Mass spectrometry (MS): measures the mass of the molecule and compares it with the mass calculated from the sequence. This test confirms identity.
HPLC: separates the components of the sample and reports the share of the target peptide as a percentage. This test reports purity.
Lot number: connects the certificate to one specific production batch and to the number printed on the vial.
Both tests are needed, because each one answers a different question. Our guide mass spectrometry vs HPLC explains how to read the two results in one minute. Products with a certificate of analysis on file are collected under lab-tested peptides.
Research areas: what peptides are studied for
Research peptides are tools for laboratory questions. Each compound is linked to a receptor or a biological pathway, and researchers group them by the area in which they are studied. The range at peptidebio follows these areas:
Tissue repair models: BPC-157 and TB-500, studied in tendon, ligament, muscle and gut tissue models. See repair and recovery research peptides.
Incretin and metabolic research: Semaglutide (GLP-1 receptor), Tirzepatide (GLP-1 and GIP receptors) and Retatrutide (GLP-1, GIP and glucagon receptors). See GLP-1 and metabolic peptides.
Growth hormone axis: Ipamorelin, a selective agonist of the ghrelin receptor.
Ageing and circadian research: Epitalon, a tetrapeptide studied in telomerase and circadian models.
These descriptions name research areas. They are not statements about an effect in humans. For most research peptides, the published data come from cell cultures and animal models. The complete range is listed under all research peptides.
Regulatory status: why research peptides are for laboratory use only
Research peptides are sold as research chemicals. They are not medicines, food supplements, foods or cosmetics. A medicine needs a marketing authorisation, for example from the European Medicines Agency or a national authority. This authorisation requires clinical trials, controlled manufacturing and approved product information. Research peptides do not have this authorisation.
Several research peptides are also listed by the World Anti-Doping Agency. The WADA Prohibited List names BPC-157 in class S0 (non-approved substances), which covers substances without approval for human therapeutic use. Rules on import and possession differ between countries. Buyers outside the EU should check the rules of their own country before they order.
For these reasons peptidebio supplies all compounds strictly for laboratory research. We give no dosing or medical advice. Questions about a specific product go to our customer service team; the contact page is linked in the footer.
Frequently asked questions about peptides
Are peptides the same as amino acids?
No. An amino acid is a single building block. A peptide is a chain of at least two amino acids that are joined by peptide bonds.
Are collagen peptides the same as research peptides?
No. Collagen peptides are a food product. They are a mixture of many different fragments from digested collagen. A research peptide is one defined sequence with a documented identity and purity.
Why are research peptides supplied as powder and not as a solution?
Water starts most degradation reactions. As lyophilised powder in a sealed vial, a peptide stays stable much longer than in solution. The solvent is added in the laboratory. Our guide on bacteriostatic water per vial explains how the volume is chosen.
How long can a sealed peptide vial be stored?
For long-term storage, keep sealed vials at -20 °C, dry and dark. For a few weeks, 2 to 8 °C is sufficient. The certificate of analysis and the product page state the conditions for each compound.
Sources for this guide to peptides
Muttenthaler M, King GF, Adams DJ, Alewood PF (2021). Trends in peptide drug discovery. Nature Reviews Drug Discovery 20(4):309–325. PubMed 33536635
Lau JL, Dunn MK (2018). Therapeutic peptides: Historical perspectives, current development trends, and future directions. Bioorganic & Medicinal Chemistry 26(10):2700–2707. PubMed 28720325
Merrifield RB (1963). Solid phase peptide synthesis. I. The synthesis of a tetrapeptide. Journal of the American Chemical Society 85(14):2149–2154. doi:10.1021/ja00897a025
World Anti-Doping Agency. The Prohibited List. wada-ama.org
For laboratory research use only. Not for human or veterinary use. Not a medicine, supplement, food or cosmetic. This guide is not dosing or medical advice.