In this video, we're going to begin our lesson on antibodies. And so antibodies are defined as why shaped proteins that are actually produced by plasma cells and they have the ability to bind very specifically to antigens and generate an immune response. Now, antibodies are also sometimes called immunoglobulins, and abbreviated as I. G, and although there are five different classes of antibodies that will talk more about moving forward in our course, typically anybody's have the same general structure. And so in our next lesson video, we're going to talk more details about the structure of the antibody. And so I'll see you all in that video.

So from our last lesson video, we already know that antibodies are why shaped proteins. But in this video, we're going to talk more details about antibody structure. And so anybody's actually consists of four poly peptide chains, two of which are identical light chains or L chains for short. And the other two are identical heavy chains or H chains. For short. Now, the light chains are actually much lighter than the heavy chains, which are much, much heavier and larger. Now these four chains are covertly linked together via di sulfide bonds. And so if we take a look down below at our image notice we have our Y shaped antibody right here and notice that are y shaped. Anybody has four poly peptide chains, It has this light chain that is identical toe this light chain over here, and then it has this heavy chain right here that is identical to this heavy chain right here. And so you can see that the heavier chains highlighted in green are much larger and therefore much heavier than the lighter chains which are much smaller and much lighter and mass, and also noticed that these four chains are covertly linked together via these die sulfide bonds that exists between the are groups of Sistine Residues. Now what's also important to note is that each of these light and heavy chains has a variable region also known as a V domain, as well as a constant region also known as a C domain. Now, the variable region or the V domain, is going to be located at the tip of each of the prongs of the why, and it contains the n terminal end of each of the poly peptide chains. So if we take a look down below at our image, notice that the V or variable domain is highlighted with the green background right here at the tips of the prongs of the why and notice that it also contains the end terminal end or the free amino groups of each of the four Poly peptide chains. Just like what we said up above now, what's also important to note is that the V Domain contains the anti gen binding site. So this is where the antibody is going to bind to the antigens at thes two potential positions indicated by the arrows. And so the reason it's called the V or variable domain, is because this region right here will actually vary between different antibodies. Now the sea domain. On the other hand, because it's the constant domain, it's not actually going to vary. It's going to remain constant, even between different antibodies. Now the sea domain is, of course, going to be the rest of the antibody. So it's gonna be located at the hinge and the stem of the Y. So if we take a look down below, of course, the sea domain eyes going to be the rest of the antibody here. And the C domain is important because it's actually recognized by immune system cells. And so, essentially, what happens is the V domain will bind to the antigens at these positions, and then an immune system cell combined to the sea domain. And so the antibody can act as an intermediate between the immune system cells and the antigens. Now, what you'll notice is in our image. Here we have. We have the V domain here with the V s on them, and then whether or not they're light or heavy chains is indicated by the L and the H, and so you can see that both the, uh, heavy chain here and the light chain has a a variable domain as well as a constant domain. And so what's important to note is that we can further break up the structure of this antibody if we imagine breaking the antibody at the hinge of the why. And so here, in a dotted red line, what we have is an imaginary line. If we were to break our anybody right at the hinge and what that would do is it would leave us with the top portion here, which we would refer to as the F A B region. And this is because this, uh, has the fragment that has the antigen binding site. So you can see we have the antigen binding site in this region. And then we're also left with the bottom half of the anybody down below, uh, which would be the F C region or the fragment that contains the constant region. So this would be the F C region, this bracket right here and so really, this is the structure of a typical antibody and we'll be able to get some practice applying the concepts that we've learned as we move forward in our core. So I'll see you guys in our next video

in this video, we're going to talk about antibody diversity. And so it turns out that our immune systems have the potential to produce an enormous amount of different antibodies, perhaps greater than 10 to the 18th or one quintillion, different antibodies. That's more antibodies than the estimated amount of individual grains of sand on our entire planet. That's a lot of antibodies that are immune system has the potential to produce. In fact, there's so many potential possibilities for antibodies that they all cannot be produced in one single lifetime. So here we have a question, and it's asking, how in the world is it possible that anybody diversity can be so large if humans on Lee have 25, genes, which is a much smaller number than one quintillion? And so the answer to this question is actually right here. And so anybody diversity actually results from significant amount of gene rearrangements, splicing and mutations. And so notice down below, over here on the left hand side, we what we have is DNA being shown, and this DNA is coding for an antibody, and so you can see that the different regions of the DNA are color coded to show you what part of the antibody that they express. And so notice that the original DNA appear has many different combinations for these different, uh, regions of the antibody. However, through splicing and rearrangements, we could get different smaller combinations, combining different features and even mutations in the DNA can create lots and lots of diversity. And so, through transcription of the DNA into RNA, you can see that even the mutation will carry over here and then through translation. What we get is the antibody being produced. And even a single slight mutation like this one right here can result in a different antibody being produced. And so we get a diverse antibody just through all of these gene rearrangements, splicing and mutations. And so this concludes our introduction to, uh, antibody diversity and in our next video will be able to talk about monoclonal and Polly clonal antibody. So I'll see you guys there