people are full of antibodies a lot of antibodies these proteins are a vital part of the immune system but just how the body makes such a variety of them mystified scientists a decade the human immune system has to fight off an endless variety of bacteria viruses and parasites and for each invader it needs a specific antibody luckily it could generate billions of them each slightly different ready for any disease but these antibodies made from two light chains into heavy chains a protein and Finian's of different proteins should need billions of genes to make them humans have around 20,000 genes the solution to this problem was a Nobel prize-winning discovery antibodies are made by b-cells like every other cell b-cells start off with the same 20,000 genes but they also have an enzyme called rag rag is a DNA shuffler it targets the genes that make the antibodies binding site there are three kinds of gene segments here called V D and J for the heavy chain of the antibody humans usually have around 130 different V segments 27 B segments and 6j segments the rag enzyme binds to one of the j segments at random and then to one of the D segment chopping off the spare DNA between them other enzymes then join the end together the same thing happens with a randomly segment so you end up with a G composed of one V one D and one J join together this provides over 20,000 possible vbj combinations for the heavy chain the light chain can have another 400 possible gene combinations combining heavy and light chain gives approximately 8 million different possible antibodies each with a different binding site and that's not all during the joining extra DNA is added or removed at the junction of the segments which takes our antibody diversity from the millions into the billion this is how our immune system can respond to diseases it's never even seen before in fact there's so much diversity that one of our antibodies could potentially bind to almost any target in the whole universe [Music]