Wikipedia, picture to the left). Polypeptides are "single linear chain of amino acids bonded together by peptide bonds", and are generally no more than 50 amino acids in length, although some would draw the line at 20 amino acids. A polymer is "a large molecule (macromolecule) composed of repeating structural units. These subunits are typically connected by covalent chemical bonds."
Amino acids are organic molecules that contain an amine group (the nitrogen) and a carboxylic acid group (the carbon with the double bonds to oxygen) and a side chain (the R in the picture). Amino acids are critical to all forms of life as they are the building blocks for proteins and peptides.
A peptide bond is the covalent chemical bond (where the atoms share their electrons) between molecules when the carboxyl group of one molecule reacts with the amine group of the other, producing water in a condensation reaction.
A protein is a biochemical compound with one or more polypeptides. Proteins and polypeptides both contain peptide bonds, but polypeptides tend to be a nice linear chain of molecules while proteins are huge messes of folded molecules that can be massive!
In bath & body products we see proteins, amino acids, and polypeptides as active ingredients all the time, and I'm writing this post as a precursor to a few posts on various peptide and polypeptide cosmeceuticals. So a peptide is a short chain of amino acids linked together by peptide bonds. The shortest one is a dipeptide with two repeating units, then we get a tripeptide, tetrapeptide, and so on - these are called polypeptides (poly meaning "more than one", which means by definition all of the peptides we see in our cosmeceuticals are polypeptides as they have at least two portions held together by the peptide bond). A protein consists of one or more polypeptides and tend to be quite messy.
Peptides tend to do well in acidic pH environments, which isn't an issue because how many of our products are alkaline? Everything we make - except CP soap - should have a pH of 7.0 (neutral) or lower anyway, so that works for us!
A lot of the peptides we use are found in our bodies and have very specific functions in a living creature, and a lot of them are not able to penetrate our skin in a way that is beneficial. Most of the polypeptides are modified to be more available for our skin, and you might see that your peptides are listed as being hydrolyzed or processed or enzymatically digested to be smaller and more able to penetrate our skin.
Join me tomorrow as we take a look at a few cosmeceuticals that include peptides.