so we are going to be just focusing on antibodies for this particular video if you remember in the previous videos talking about B lymphocytes you see under normal circumstances when the pathogen enters our body you will be sick for the first time especially during the primary immune response I told you that when B lymphocytes get stimulated they will undergo clonal expansion and then they will form these types of cells know know as plasma cells and plasma cells will produce and release antibodies and as long as the antibodies bind to the antigens of the pathogen I told you that usually you will start to feel better and recover from the infection um so what exactly are antibodies all about the first thing I want you to understand is antibodies are not to be confused with antibiotics they are two different things by the way antibiotics are medications or drugs that we put into our body in an attempt to destroy or kill bacteria antibodies however are different so first question first what exactly are antibodies so so if you remember in chapter 2 of biological molecules I showed you before in this video when we were when we were discussing protein structures and under protein structures I think I showed you this diagram of the anti antibody and of course as a student when you look at this diagram of an antibody molecule you might go oh God this is so complicated what exactly is this all about so let's try to simplify this the first thing to understand about antibody is it's structure the structure of the antibody is referred to as quinary globular glycoproteins why is it a protein because the monomers are amino acids linked together by peptide bonds chapter 2 why is it globular well antibody you can argue that it's a spherical shape or a ball shape it doesn't really look like a ball shape if I'm being honest with you but the more important thing is antibodies are water soluble so the fact that they are water soluble classifies them as a globular protein the reason why they are quinary is because the antibody is a protein that is made up of more than one polypeptide chain for example antibodies are made up of four chains by the way away all right and why glycal because it is attached to some sugars so if you look at this ribbon diagram it's quite complicated I'm going to simplify that ribbon diagram by drawing out the four polypeptide chains if you notice in the complicated diagram there were four colors there's blue green um red or pink and then there's like a gold color so those are the four polypeptide chains and notice in the four polypeptide chains it looks it looks quite some of the chains are long and some of the chains are short okay so these are the four chains that make up one antibody molecule so to describe the antibody molecule in terms of its structure more in detail the antibody is made up of four chains but two of the chains are heavy chains or long chains and two of the chains are light chains or short chains and those chains are linked together by what bonds are this by the way these are known as d sulfide Bridges and if you remember D sulfide bridges are extremely strong calent bonds as well and because it's a glycoprotein I'm just attaching some sugar molecules uh right there now and notice the purple color area I am referring to that area as the antigen binding site all right I'm going to explain this so that means what that means is that is the part of the antibody molecule that is supposed to attach to the antigen so one antibody molecule can bind to two antigens because it has two antigen binding sites now another very important thing I want you to understand here is the black color lines are referred to as something called constant region and the purple color or the maroon color or magenta I don't know what color that is uh that is referred to as the variable region so you might be thinking okay so what does this mean actually okay why why is there a constant Reg and variable region well if you remember your body has many different types of B lymphocytes not compare the B lymy on the left and the right what's the difference they both have different shaped receptors as you can see there obviously which means that they will both respond to different shape of antigens and when they both respond to different shapes of antigens they will undergo the immune response and develop something called plasma cells but the plasma cells on the left and the plasma cells on the right they will they will both release antibodies but notice the shape of the antibodies the shapes of the antibodies are different obviously because they have to bind to complementary antigens now what I'm doing is I'm just focusing on one of the antibody for each of the plasma cells so notice the shape okay even though the shapes of the two antibodies here are technically different look at the black color part the constant region for both of them are exactly the same which means to say that in the black color lines they have the exact same amino acid sequence for the antibody on the left and the antibody on the right all right what becomes different is their antigen binding site because obviously this antibody has to bind to a different antigen and this antibody has to bind to a different shaped antigen right so when you compare their amino acid sequences the amino acid sequences for the variable regions will be different as I'm showing you based on the shapes yeah so you can see the the one on the left it has circle triangle triangle circle circle but the one on the right is triangle circle square square triangle so because they have different amino acid sequences they will form a different 3D structure and this is good because when they have different 3D structures they can bind to different types of antigens that is why the black color area is referred to as the constant region because for the antibody on the left and the antibody on the right their amino acid sequences are exactly the same but the purple color area is referred to as the variable region because the amino acid sequences are different so that they are able to bind to different antigens that's basically it so then comes the question what exactly do antibodies do in our body before we try to understand how antibodies help us during infections we must first try to understand what pathogens do in our body for example if you had a virus that entered your body the virus will infect our body cells it will force our cells to make more viruses and it will the virus usually bursts out of the cell and kills our cells in the process very rude of the viruses to do something like that now in some cases also bacteria that have flagella may be moving too fast in our body and the fyes because they're trying to kill trying to ingest the bacteria uh they cannot they cannot catch up to the bacteria because the bacteria are moving too fast so the fyes may have difficulty uh capturing the bacteria so that's an issue some bacteria also produce toxins in which toxins are just uh harmful substances and when the toxin hits your cell they will damage our cells so this is quite bad for example in the chera bacterium vibrio they will produce a toxin known as cheren and when the cheren hits your small intestine epithelium cells it will cause you to have diarrhea that's an example of a toxin by the way don't have to memorize the name of the toxins all right so how exactly do antibodies help us prevent all this from happening very simple look at the virus viruses normally infect our body cells correct the antibodies can then actually bind to the complimentary antigens on the virus and when they bind to the compliment antigens of the virus guess what the virus cannot infect our cells they cannot enter the cells and if they cannot enter the cells can they replicate no so you will stop viral replications in your cell and that's a good thing okay so the amount of viruses in your cells will not increase because the antibodies have attached to the antigens and they preventing the viruses from going into your cell number two remember there was another problem where the bacteria are moving too fast in your body so what happens is the antibodies can bind to the flugel on the bacteria and when they bind to the flugel it will prevent the bacteria from moving too fast so the bacteria movement slows down and the fosite can catch up and eat it up basically so it's easier for phagocytosis to happen the third problem was some bacteria or some pathogens can produce toxins which are damaging to our cells so the antibodies can bind to the toxins and when they bind to the toxins the toxins are unable to cause damage to your body cells this is called neutralization of toxins so you see the antibodies can do one of these three things that help help us mitigate the damage caused by the pathogens now um sometimes uh because pathogens are spreading around very easily what happens is the antibodies can Clump the pathogens together okay and clumping the pathogens together just means they can stick the pathogens together notice the antibodies here the the the part of the antibody can kind of stretch out because it has something referred to as a hinge region the hinge region provides more flexibility to the antibody molecule and then uh it allows it to bind to different antigens simultanously so that's a good thing but the shape of the antigen has to be the same and of course in this case the antibodies when they Clump the pathogens together the pathogens cannot move freely and when the pathogens cannot move freely the fyes can come and ingest them the last thing that antibodies can also do is something known as opsonization you don't have to remember the word opsonization but it's uh you have to know what it means now fyes under normal circumstances are supposed to ingest bacteria or viruses the problem is figos sites are sometimes dant as well or inactive so you see even if there's a pathogen nearby it may not realize that there's a pathogen nearby right but what you have to understand is the fosite also have receptors and The receptors are not complementary to antigens okay this receptor is not complimentary to the antigen but it's complementary to antibodies heavy chain which is the heavy chain by the way the heavy chain is remember the long ones so when the antibody binds to the complimentary antigen on the pathogen the heavy chain which is the part where I'm highlighting in purple that's the one that will actually bind to The receptors on the Figo site when they bind to The receptors on the Figo site it will stimulate the fosite and when it stimulates the fosite it tells the fosite hey we have a lot of pathogens in the body I have already attached to the antigens can you please ingest them ingest and digest them as soon as possible so antibodies can also attach to receptors on figos sites and increase the rate of Figo cytosis so these are the five ways in which antibodies can actually defend our our body against infections they will bind to antigens on the virus preventing them from infecting our cells they will slow down bacteria by attaching to the Flaga they will also bind to toxins and neutralize them they Clump pathogens together and they increase the rate of Phagocytosis and when all of this happens you recover from the infection under normal circumstances