Peptide fundamentals
Start here if a word on a certificate or product page has ever stopped you. The rest of the site builds on these terms.
What exactly is a peptide?
It is a short string of amino acids held together by peptide bonds. By convention, chains of up to about 50 amino acids count as peptides and longer ones as proteins. That cut-off is a habit of the field, not a hard rule. Retatrutide has 39 amino acids, so it is clearly a peptide.
What holds a peptide chain together?
A peptide bond: a covalent link between neighbouring amino acids. It forms when the amino group of one reacts with the carboxyl group of the next, and a molecule of water is given off. The bond is strong and stiff. So the sequence survives ordinary handling well, while the folded shape is much easier to disturb.
Where do amino acids fit in?
Amino acids are the units that peptides and proteins are assembled from. Living systems use twenty standard ones. Each has the same core backbone and its own side chain. The sequence they are linked in decides how the molecule folds. The fold, in turn, decides what the molecule can bind.
What is a receptor, in simple terms?
A receptor is a protein, usually set in the outer membrane of a cell, that one particular kind of molecule can attach to. When that happens, the receptor changes shape and sets off a chain of signals inside the cell. Receptors are picky. Whether a compound fits a given receptor decides whether it does anything there.
What does molecular weight tell you?
It is the mass of a single molecule, given in daltons (Da) or grams per mole. It matters on a certificate because mass spectrometry uses it to confirm identity. The lab works out the expected mass from the sequence, then measures the real one. The two should agree within a narrow margin.
How is an agonist different from an antagonist?
Both attach to the same receptor. What differs is the outcome. An agonist turns the receptor on and a response follows. An antagonist sits in the receptor without turning it on, which keeps the natural messenger out. Picture one pressing a light switch and the other taping over it.
What does an agonist do?
An agonist attaches to a receptor and switches it on. The response resembles the one the body's own messenger molecule would trigger. Agonists differ in how hard they push. A full agonist can reach the highest possible response. A partial agonist stays below that ceiling, even with every receptor occupied.
How does in vitro differ from in vivo?
In vitro work takes place outside a living organism, in lab vessels. In vivo work takes place inside one. The in vitro setting lets you study one variable cleanly. But it leaves out absorption, distribution, metabolism and clearance. That gap is why a compound can act one way in a dish and another way in a living system.
What is meant by in vitro?
The Latin means “in glass”. It describes work done in a controlled container, such as a tube, a well plate or a dish, rather than inside a living organism. Research-grade peptides are supplied for exactly this kind of work. A result in a dish is not a forecast of what a whole organism would do.