So as you guys are reading through your textbooks or sitting in class, listening to your professors, you might hear these 5 protein-related terms just tossed around and used all the time. But not everyone distinguishes between these 5 protein-related terms. And so here in this video, we're going to specifically distinguish between these 5 protein-related terms. And so these 5 protein-related terms are referring to amino acid chains that vary in their length. And so notice down below we have this table that has the protein-related terms over here on the left-hand side, and then it has the length of the amino acid chain over here on the right-hand side.

And so the first protein-related term that you all should know is, of course, amino acid, which we already talked about in our last lesson video. So, we already know that amino acids are a single protein unit or, in other words, a monomer of a protein is an amino acid. And then of course we can take these individual monomers, these individual amino acids and link them together to create a long chain of amino acids. And that's where these other four terms come into play. So the second term that we have here is going to be oligopeptide.

And so recall that the oligo prefix means a few. And so oligopeptides are going to have an amino acid chain that have just a few amino acids, somewhere between about 2 and about 20 covalently linked amino acids in the chain. So pretty short, amino acid chains are oligopeptide chains. Now the term peptide without the oligo prefix is referring to amino acid chains that have less than 50 covalently linked amino acids. And so what's important to note here is that oligopeptide and peptide at some point there's a little bit of overlap between the two terms.

Now the 4th term that we have here is polypeptide, and recall that the prefix poly means many, and so these are going to be amino acid chains that have greater than 50 amino acids that are covalently linked together. And then the 4th the 5th and final term that we have here is protein itself. And so a protein is specifically referring to just 1 or multiple polypeptide chains that are specifically in their folded or functional forms. And so when we're talking about proteins, we're talking about polypeptides that are in their folded or functional forms. And when we say folded, what we mean is that these chains don't just remain as straight linear chains, they actually fold up into themselves and create these complex three-dimensional structures.

And so really this leads us to our next lesson video which is talking about the levels of structure of protein. So I'll see you all there in that video.