From the venom of the cone snail to the cocoa in your chocolate bar — peptides are everywhere. Explore, calculate, and discover the molecules that shape life.
A peptide is a short chain of amino acids — the same building blocks that make up proteins, but linked in sequences typically ranging from 2 to about 50 residues. Despite their small size, peptides are extraordinarily diverse: they act as hormones, antibiotics, neurotransmitters, and toxins. Your body produces thousands of different peptides every day, coordinating everything from digestion to immunity to mood.
Known as the "love hormone," oxytocin is a nonapeptide produced in the hypothalamus. It plays a central role in social bonding, trust, and childbirth — and is one of the most studied peptides in neuroscience.
Your body is a peptide factory. The human proteome encodes thousands of bioactive peptides that carry out indispensable roles — from regulating blood sugar after a meal to transmitting pain signals in milliseconds.
The body's chemical messengers. Insulin (51 AA, from pancreatic β-cells) regulates blood glucose after meals; glucagon (29 AA) raises it when levels drop. Oxytocin (9 AA) triggers uterine contractions and milk ejection, and plays a key role in social bonding. These hormones act at nanomolar concentrations.
Peptides that transmit or modulate signals in the nervous system. β-Endorphin (31 AA), released during intense exercise, binds opioid receptors and produces natural pain relief. Enkephalins (5 AA: Met-YGGFM and Leu-YGGFL) are the brain's endogenous analgesics. Substance P (11 AA) amplifies pain signals.
The innate immune system's first line of defense. Human β-defensins (18–45 AA) punch holes in bacterial membranes. Cathelicidin LL-37 (37 AA) is active against bacteria, fungi, and enveloped viruses. Over 3,000 natural antimicrobial peptides have been catalogued — a major focus in antibiotic resistance research.
Peptides that orchestrate digestion. Cholecystokinin (CCK, 33 AA) triggers gallbladder contraction and pancreatic enzyme release. Secretin (27 AA) prompts bicarbonate release to neutralise stomach acid. Ghrelin (28 AA), produced in the stomach, is the primary hunger signal before meals.
Atrial natriuretic peptide (ANP, 28 AA) lowers blood pressure by promoting sodium excretion by the kidneys. Bradykinin (9 AA) dilates blood vessels. Angiotensin II (8 AA) is a potent vasoconstrictor; drugs that block its formation (ACE inhibitors) are among the most widely prescribed medicines worldwide.
Thymosin α1 (28 AA), secreted by the thymus, promotes T-cell maturation and has been used clinically to boost immune responses. Thymulin (9 AA) is essential for T-cell development. Tuftsin (4 AA: Thr-Lys-Pro-Arg), cleaved from immunoglobulin G, stimulates macrophage phagocytic activity.
Practical tools for researchers, students, and anyone curious about peptide biochemistry.
Enter any peptide sequence and instantly get molecular weight, formula, and net charge at physiological pH.
Open tool →Calculate the isoelectric point of any peptide sequence — the pH at which the molecule carries zero net charge.
Open tool →Visualize the Kyte-Doolittle hydrophobicity profile of your peptide.
Open tool →Convert between 1-letter and 3-letter amino acid codes instantly.
Open tool →Searchable reference of 200+ peptides — filter by source, type, length, or MW.
Browse →Complete reference of all 20 standard amino acids with codes, MW, pKa, and hydrophobicity.
Open →From scorpion venom to the cocoa in your chocolate — peptides shape the natural world in remarkable ways.
Venoms, silk, frog secretions — how the animal kingdom uses peptides as weapons and signals.
Explore →From Fischer's 1901 synthesis to Nobel Prizes, blockbuster drugs, and modern solid-phase synthesis.
Read →The most toxic, most expensive, longest, fastest-acting — the extremes of the peptide world.
See records →Clear definitions of 100+ peptide science terms, explained without excessive jargon.
Browse glossary →Many of the peptides you encounter aren't made by your body — they're in your diet. Some form during food processing or fermentation, others are released when digestive enzymes break down food proteins.
Casein (~80% of milk protein) releases bioactive peptides during digestion. β-Casomorphins (7 AA) bind opioid receptors in the gut. Lactotripeptides IPP (Ile-Pro-Pro) and VPP (Val-Pro-Pro), concentrated in fermented dairy, are well-characterised ACE inhibitors studied in clinical trials as natural antihypertensives.
Fermentation is a powerful peptide generator. Aged cheeses accumulate ACE-inhibitory peptides over months. Japanese natto contains nattokinase (a fibrin-cleaving enzyme) plus antioxidant peptides from soy proteins. Soy sauce and miso, produced by Aspergillus fermentation, are rich in short peptides and glutathione precursors.
Collagen's triple helix is built from Gly-X-Y repeats, where X is often proline and Y is hydroxyproline (Hyp). Digestive enzymes release characteristic peptides — especially Pro-Hyp and Hyp-Gly — from collagen-rich foods. Stable-isotope labelling studies show these peptides are absorbed intact and appear in blood within 1–2 hours.
In normal digestion, gluten proteins are fully broken down. In celiac disease, a single gliadin fragment — the 33-mer (33 AA) — resists all human digestive enzymes and triggers an immune cascade in the small intestine; it is considered the primary immunogenic driver of the disease. Wheat exorphins, opioid-like peptides from gluten digests, have also been characterised biochemically.
Dark chocolate contains cocoa-derived peptides formed during fermentation and roasting of cacao beans.
Spider dragline silk is made of spidroin proteins — long polypeptide chains with repeating motifs of glycine and alanine.
Oxytocin, the molecule of bonding and trust, is a tiny nonapeptide: just 9 amino acids in a ring structure.
The gut and brain communicate through peptide hormones. Ghrelin signals hunger, while GLP-1, released after eating, tells the brain satiety has been reached.