Peptides show up everywhere in biology and in research labs, but the term is often used loosely. Here is a plain-language look at what a peptide is, how it differs from a protein, and why scientists study them.
The short answer
A peptide is a short chain of amino acids linked together by chemical bonds called peptide bonds. Amino acids are the building blocks of all proteins. Link two of them and you have a dipeptide. Link a few dozen and you have a polypeptide.
Peptide vs. protein
The line between the two is about size and structure. Peptides are generally chains of about 2 to 50 amino acids. Proteins are longer chains, often hundreds of amino acids, that fold into complex three-dimensional shapes. The cutoff is a convention, not a hard rule, so you will see some molecules described both ways.
Examples found in the body
- Glutathione: 3 amino acids. A major antioxidant inside cells.
- Oxytocin: 9 amino acids. A hormone involved in childbirth and social bonding.
- GLP-1: about 30 amino acids. A gut hormone that helps regulate insulin and appetite.
- Insulin: 51 amino acids across two chains. Often called the smallest protein or the largest peptide hormone.
What peptides do
Many peptides act as signals. They bind to receptors on the surface of cells and switch specific processes on or off. Peptide hormones regulate blood sugar, digestion, growth, sleep and stress responses. Other peptides act as antimicrobials, neurotransmitters or structural fragments of larger proteins.
How peptides are made
In living cells, ribosomes assemble amino acids into chains based on instructions from DNA. In the lab, most research peptides are built with solid-phase peptide synthesis, a method developed by Robert Bruce Merrifield in the early 1960s. It adds one amino acid at a time to a chain anchored on a resin bead. The method was so important that Merrifield received the 1984 Nobel Prize in Chemistry.
After synthesis, peptides are purified, often by high-performance liquid chromatography (HPLC), and their identity is confirmed by mass spectrometry. Purity testing is one of the main quality checks for research-grade material.
Why researchers study them
Peptides are highly specific: a given peptide tends to bind one target receptor, which makes them useful tools for studying how biological systems work. That specificity is also why peptide-based medicines, from insulin in the 1920s to modern GLP-1 drugs, have become a major area of drug development.
Handling and storage basics
Research peptides are usually supplied as a freeze-dried (lyophilized) powder, which is more stable than a liquid. In the lab they are typically stored cold and away from light, and reconstituted with a sterile diluent such as bacteriostatic water when needed. Always follow the storage guidance on the product documentation.
This article is for educational purposes only and is not medical advice. Products sold by Cacti Research Solutions are for research/laboratory use only. Human or animal use and/or consumption is strictly prohibited.
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