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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.

In just over a decade, GLP-1 research moved from twice-daily injections to once-weekly dosing and then to molecules that hit two or three hormone receptors at once. Here is a short timeline of how the field got here.

Semaglutide and the weight-loss shift

Novo Nordisk’s semaglutide was approved for type 2 diabetes as the weekly injection Ozempic in 2017, followed by an oral tablet, Rybelsus, in 2019. In the STEP 1 trial, adults with obesity lost about 15% of body weight on average over 68 weeks, and the FDA approved semaglutide for chronic weight management as Wegovy in 2021.

Heart outcomes

The SELECT trial, reported in 2023, followed more than 17,000 adults with overweight or obesity and existing cardiovascular disease but no diabetes. Semaglutide cut major adverse cardiovascular events by about 20% compared with placebo, which moved the conversation beyond weight alone.

Two receptors: tirzepatide

Eli Lilly’s tirzepatide activates both the GIP and GLP-1 receptors. It was approved as Mounjaro for type 2 diabetes in 2022 and as Zepbound for weight management in November 2023. In the SURMOUNT-1 trial, the highest dose produced an average weight loss of about 21% over 72 weeks.

Three receptors: retatrutide

The next step under study is retatrutide, an investigational triple agonist of the GIP, GLP-1 and glucagon receptors. In a phase 2 trial published in 2023, the highest dose produced an average weight loss of about 24% at 48 weeks. Phase 3 studies are ongoing, and the compound is not approved by the FDA.

What to watch

Current research is focused on oral small-molecule GLP-1 agonists, combination therapies, and new uses in conditions such as sleep apnea, kidney disease and liver disease. Watch for phase 3 readouts and FDA decisions as the field keeps moving.

This article is for educational purposes only and is not medical advice. Products sold by Cacti Research Solutions are for research/laboratory use only.

One of the most unlikely turns in GLP-1 history runs through the desert Southwest. The Gila monster, a slow-moving venomous lizard that can go months between meals, turned out to carry a molecule that changed diabetes research.

A discovery at the VA

In the early 1990s, John Eng, an endocrinologist at the Bronx VA Medical Center, was screening animal venoms for new hormones. In 1992 he reported exendin-4, a peptide from Gila monster venom that shares about half its sequence with human GLP-1 and activates the same receptor.

Built to last

The key difference: exendin-4 resists breakdown by the DPP-4 enzyme. Where human GLP-1 lasts only minutes in the bloodstream, exendin-4 lasts for hours. That durability solved the main obstacle that had kept GLP-1 from becoming a practical therapy.

Exenatide reaches the market

Eng patented the peptide and licensed it to Amylin Pharmaceuticals, which developed a synthetic version called exenatide with Eli Lilly. The FDA approved it as Byetta in April 2005, making it the first GLP-1 receptor agonist on the market. It was taken by injection twice a day.

The race for longer action

Exenatide opened the door. Novo Nordisk took a different route, modifying human GLP-1 with a fatty acid chain that binds albumin and slows clearance. The result, liraglutide, was approved in the U.S. in 2010 for type 2 diabetes as a once-daily injection, setting up the next decade of longer-acting compounds.

This article is for educational purposes only and is not medical advice. Products sold by Cacti Research Solutions are for research/laboratory use only.

Long before GLP-1 became a household name, researchers noticed something odd: glucose taken by mouth triggers a much larger insulin response than the same amount of glucose delivered straight into a vein. The gut, it seemed, was sending its own signal to the pancreas.

A century-old idea

The concept of gut hormones dates to 1902, when William Bayliss and Ernest Starling described secretin. In 1932 the Belgian physiologist Jean La Barre coined the term “incretin” for a gut factor that lowers blood sugar. When reliable insulin assays arrived in the 1960s, the oral versus intravenous glucose experiments put hard numbers behind the idea, which became known as the incretin effect.

From GIP to the proglucagon gene

The first incretin identified was GIP (glucose-dependent insulinotropic polypeptide) in the 1970s. The second came from molecular biology. In the early 1980s, cloning of the proglucagon gene revealed that it encodes more than glucagon. It also carries two related sequences, later named glucagon-like peptide-1 and glucagon-like peptide-2.

Finding the active form

Work in the mid-1980s, including research by Svetlana Mojsov and Joel Habener in Boston and by Jens Juul Holst in Copenhagen, showed that a truncated form of GLP-1 strongly stimulates insulin release in a glucose-dependent way. Daniel Drucker and others helped map its wider biology, including effects on glucagon, gastric emptying and appetite.

The catch: a two-minute half-life

Natural GLP-1 is broken down by the enzyme DPP-4 within minutes, which made it nearly useless as a drug on its own. Solving that problem became the next chapter of the story. In 2024, Habener, Mojsov and Novo Nordisk scientist Lotte Bjerre Knudsen received the Lasker-DeBakey Clinical Medical Research Award for their roles in the discovery and development of GLP-1 based medicines.

This article is for educational purposes only and is not medical advice. Products sold by Cacti Research Solutions are for research/laboratory use only.