Antibodies | Immunoglobulins | Structure & Function | Part 1

today we will be talking about antibodies immunoglobulins right the concepts about immunoglobulins are very important these are one of the most important molecules in our body you cannot survive without them in such a hostile world where there are so many microbes and so many path pathogens which are trying to invade our body and destroy destroy our tissue now exactly what are antibodies anti bodies they are also called immuno yes please immunoglobulins now what are exactly antibodies from where they come in our body and exactly where they are present right major portion of the antibodies circulating in the blood right antibodies are special protein molecules antibodies are very special type of protein molecules which are secreted by plasma cells antibodies are special type of protein molecules which are secreted by the plasma cells now what what is a plasma cell actually whenever a b lymphocyte whenever a b lymphocytes becomes fully differentiated and becomes fully functional right it start producing antibodies it starts secreting y shaped molecules or antibodies so antibodies are the products of proteinaceous product of well differentiated b cells or protein products of plasma cells is that right now exactly in the blood in which component of the blood antibodies are present yes please question goes to very impressive doctor dr safa in which component of the blood antibodies are present let's come with very simple thing everyone knows that blood has two components cell then yes please plasma and plasma has many components is that right one of the component is plasma proteins actually antibodies are the part of the plasma proteins that's a very basic concept that where antibodies are antibodies are present yes present in your blood as the proteinaceous component of the plasma the plasma has many type of proteins now we have to see that within the plasma and within the plasma protein where antibodies are exactly present so dr israel may answer us that your plasma has proteins and one component of the plasma proteins are basically antibodies now uh which component of the plasma protein is having antibodies i'm about to be impressed by him i think he's very serious right now he doesn't want to answer so i will do it myself look one of the way let's suppose that on this filter paper we put a drop of plasma right we put all the plasma proteins here we put all the plasma proteins here you know plasma proteins are positively charged or negatively charged you like to keep secrets you don't tell me plasma proteins are negatively charged is that right at body ph which is 7.4 by the way at the body ph plasma proteins are negatively charged now because most of the plasma proteins are negatively charred if you put a drop of plasma on this filter paper and you run the current across it for example you put negative electrode here and positive electrode here of course plasma proteins will move from negative electrode towards positive electrode because plasma proteins are themselves negative so they will be repelled by the negative and of course they will be attracted to the positive so plasma protein will start moving now as plasma proteins start moving this segregate into group because all the plasma proteins don't move right with the same speed on this paper you can answer this if plasma protein is very heavy right that will move fastly or slowly slowly actually those plasma proteins which are more negative and smaller in molecular weight they will be more smart and they will rush fastly so what really happens that some of the plasma proteins will reach here right then there will be some here here and here and here now these are the plasma proteins which are smallest in molecular weight right and they're more mobile right so they will come over here this was the movement right heavier plasma proteins will be left behind is that right if you divide the plasma protein or segregate the plasma protein by this way this is called process of electrophoresis have you heard of it process of electrophoresis when you do electrophoresis of the plasma proteins right this electro is that right now electrophoresis when you do the plasma proteins the smallest molecule weight will be here and as the plasma proteins become more and more heavier they are segregated in a different band right actually these plasma proteins as a group are called just place albumins because albumins are the smallest molecular weight and this whole group of plasma proteins this three this is called globulins globulins and this is supposed fibrinogen is that right another way to show this is that you draw a graph graph is that if you put molecular weight here and you are classifying the plasma protein according to the increasing molecular weight on this side and plasma protein concentration on the side then this is albumin what is this this is albumin and these are globulins am i clear now out of this this is alpha globulin these are beta globulins these are gamma globulins it means primarily plasma proteins are albumin and globulins and globulins can be separated global in the globular protein can be separated right according to the molecular weight into alpha globulins beta globulins and gamma globulins is that right am i clear albumin's molecular weight is about approximately 70 kilo delta but global length molecular weight is from 90 to 120 kilodelton hello delton right now within this shade where exactly antibodies are present that is the question now i think you should be intelligent enough to guess in this band this is albumin alpha globulin beta globulin gamma globulin and exactly where the plasma proteins are segregated israel dr safa of course they are not alpha and beta they are in gamma actually if you study if you study these plasma proteins these are antibodies if you study this band this is antibody so [Music] where are the plasma protein in your body plasma proteins are of course in the plasma but within the plasma protein where are the antibodies antibodies are part of the gamma globulins actually that is why antibodies are also given another name what is that name gamma globulins simple as that am i clear so there are three names the antibodies they are immunoglobulins these are gamma globulins now these are three same name for the same type of molecule is that right that gamma globulins mean those globular proteins which are part of the gamma fragment right or gamma band on electrophoresis of plasma protein immunoglobulins mean what those globulin proteins which have immune function they are also antibodies and what are antibodies antibodies are those protein molecules which are secreted by well differentiated b cells called plasma cells and antibodies specifically this is very important antibody molecules specifically react with antibody molecules specifically react with the antigens which stimulated the formation of those antibodies so what are antibodies antibodies are protein molecules secreted by the secreted by the plasma cells which can which react specifically with those antigens which elicited there or stimulated their formation or stimulated their synthesis am i clear no problem after this now if i give you a statement i say that antibodies are those globular proteins right which are produced by the plasma cells and they react with specifically with the antigens which lead which stimulated their formation plus i can say antibodies are also called immunoglobulins because why we call the antibodies immunoglobulins because antibody molecules are just proteins which are part of the globular globulin components of the plasma protein and which component of the globulins gamma globulins is that right so next time if i someone ask you that in your blood where the antibodies are present you say remove the cell left is a plasma outer plasma separate the proteins run the proteins electrophoretically and find the gamma band and all your antibodies will be present in gamma band am i clear there's no problem up to this now we come to really basic structure of antibody as i told you these are basically proteins with little carbohydrate component and then protein they have a little carbohydrate component we call them glycoproteins and proteins they were little carbohydrate components what we call them glycoproteins to be more specific antibodies are glycoproteins antibodies are glycoproteins now let's come to the basic structure of a typical antibody antibody is basically a tetra peptide any antibody is basically a number one condition is it is a tetra peptide when i say that antibodies are tetrapeptide it means how many peptide chains it has four it is tetrapeptide consisting of two heavy chains and two light chains a typical antibody molecule is a tetra peptide with two heavy chains and two light chains held together by yes held together by disulfide bond disulfide bonds so again what is antibody antibody is the tetrapeptide antibodies of course glycoprotein molecule right it is a tetra peptide consisting of two heavy chains and two light peptide chains all of them are held together by disulfide bond amicular and it is usually a y-shaped molecule let me make your typical antibody molecule antibody molecule should have four peptides okay i will make two heavy peptides here why we call this peptide heavy peptide or heavy chain right this is a heavy chain and there must be another there must be yes place another heavy chain so antibody has two heavy chains with that it has to yes light chains it has to light chains and there are two heavy chains and there are two light chains and they are held together by this place disulfide bonds these are the disulfide bonds which are holding them together and of course they should be held together by disulfide bonds now let's go back to the definition antibody is of course an immunoglobulins which is secreted by plasma protein present in the plasma gamma globulin component right antibodies are basically tetrapeptide the four peptides having two heavy chains and two these are two heavy chains and two light chains held together by disulfide bonds am i clear this is a typical uh you can say shape of the antibody now antibodies have the specific function of the antibodies they should bind with the antigen in a specific manner right now in which part of the antibody antigen binds yes you will tell me you could just come here and put your finger in which part of the molecule antigen will bind exactly yes just tell it hurry up i don't know top mean how many points are there where antigen can bind you don't know just come come come here you know be brave yes antigen will bind here okay no no i give you here this is antigen right very sad because it's going to bind with end you draw it there exactly where it will bind okay so it rides over there you are near the point but honestly it should be laughing here you know why because from here it can escape away no no no no no it should be in between them like here and then it will you know both chains will cooperate to catch it you see antigens are not here there they will run away is that right actually a part of a light chain and part of a heavy chain together grab the antigen this is very important to know this is one antibody molecule having two heavy chains two light chains right and one antibody molecule which i'm showing here can bind with two antigens or two epitopes of the antigen is that right now let me tell you actually the antigens which are direct sorry the antibodies which are directed against different antigens must be different in this area let me tell you what i am telling for example here is one antigen like this and other antigen is like this another antigen is do you think these antigens are same or different from each other they are different from each other and antibodies it will bind with do you think one antibiotic antibody can bind with all three of them no antibodies are very specific the antibody which will bind with this antigen will not bind with the other ones is that right every antibody is very very specific for a given antigen a closely structural given antigen now if i say that antibody body which is going to react with this it cannot react with this an antibody which react with this antigen cannot react with the other two it means this part of the molecule you know this part of the antibody molecule should be diff different in different antibodies for different antigens are you understanding for example let me tell you that i will make a simple diagram that let's suppose this is like now they can catch this antigen is that right in the same way now it will more specifically fit suppose this is antigen number one this is antigen number two this is antigen number three is that right am i clear now opposite to that if there is another antibody and which will fit into which antibodies directed for that that antibody will have some difference now do you think antigen number one can bind here no it is designed for antigen number two antigen number two can better fit over here is that right so what we see that this part of the heavy chain and the light chain is very varying from antibody to antibody when antibodies are directed against for different antigens so we say that let's suppose if we have three antibody molecules one is for this antigen other antibody molecule is for this antigen and other antibody molecules for this antigen then what will happen all those antibody molecules which are directed against different antigens should have this area with different configuration it means this area varies according to the specificity for antigen reaction that is why this part of the light chain this is the light chain this part of the light chain is variable light chain and this part of the heavy chain also vary so this is variable have you changed this component this part of of course this is a peptide chain so it should have here a minor end and here it should have carboxyl end the same with heavy chain should have one amino and another js carboxylan you understand this then every peptide chain has on one side a minor and another carboxylate so what really happens that minor end of the light chain and a minor end of the heavy chain they are having a domain domain mean and a region of amino acids sequence within a peptide chain this domain is variable so this is variable domain of the light chain this is variable domain of the heavy chain is that right but this this component this component this will not vary it is constant it is constant we call it constant of the light chain and constant of the yes please heavy chain this is variable of the heavy chain and this is constant of the heavy chain and if you come to the light chains this will be what variable of the light chain and this will be constant of the light chain is that right no problem after this let me make it more clear let's suppose there is star antigen there is spherical antigen and there is potato antenna the star antigen ball ball antigen b a double l ball antigen and potato antigen now antibodies reacting against them will be same or different different antibodies let's suppose i show the anti body for this these are the heavy chains all of them i am showing in a very simple way you can understand now these are three antibody molecules but antibody molecule which will react with the star let me show star here it is going to react with the star this part of the light chain will be variable and this part of the heavy chain will be variable of course here if on one side it is binding with the star another side will it will also bind with the star so the same variable which is here on the heavy chain here also same variable will be there and variable will be there on the light channel now if this molecule is going to be this ball antigen then what will happen now here is the let's suppose i put the ball do you think the variable regions can be same as star no so they will vary from in this area understand it now we come to this for that antigen suppose there's another antibody which specifically react with that of course it will have two heavy chains then just place two light chains right now this antigen is like this now you understand it that basically a particular antibody will react only with the specific antigen every antibody does not react with every antigen and why a specific antibody molecule react only with a specific antigen because antigen binding area antigen binding area of the antibody has variable regions and these variable regions right vary from one group of antibodies to the next group of antibodies to the next group of the antibodies as antibody group change their specificity for the antigens right now come back so this was variable domain domain of the light chain and this is the constant domain of the light chain then this is a variable domain of the heavy chain this is the constant domain of the heavy chain heavy chain has many constant domain uh constant domain number one constant domain number two constant domain number three right one constant domain number one constant domain number of the heavy chain number two or three and later on we'll find that most of the antibody classes how many antibody classes are there there are five basic classes of the antibodies right ah the five classes of antibodies are called can you tell me immunoglobulin g a aminoglobulin a class immunoglobulin m group class immunoglobulin e and immunoglobulin d we call it gamed um all the immunoglobulins can be primarily divided into five classes i will tell you later how we divide them on what what base immunoglobulins can be divided into five classes but antibodies can be divided into five classes this is immunoglobulin g aminoglobulin a amino globulin and we immunoglobulin ig now you understand why we call it aminoglobulin these are the globular proteins from the globulin component of the plasma proteins having immune function and belonging to the class of g or class of a right or class of m e out of this m e me very important you know me has longer heavy chain what does it mean that basically immunoglobulin m and immunoglobulin e has heavy chains with constant number one constant number two constant number three constant number four right so constant of the heavy chains in a immunoglobulin class m and class e is how many one two three and four but immuno amino globulin a g and d their heavy chains are having only how many constant domain constant domain number one two and three but ig m and ig g have how many one four one additional that is four is that right now let's review it antibody molecule has how many peptides a typical antibody molecule how many peptides two are heavy chains and two are light chains why light chains are called light chain because the molecular weight is less usually light chains molecular weight is about 25 000 and molecular weight of the heavy chain is 50 000 to 70 000 depending upon there are three constant of four constant region right so the four peptide held together by the disulphide bond two light chains two heavy chains in a typical antibody molecule is that right now on the amino ends of the heavy chain and a minor end of the light chain there are which areas variable areas there is variable area of the light chain there is variability of the heavy chains in between these two variable area what is fitting their antigen fats is that right so antibody uh binds with the antigen through the heavy chain as well as through the light chains through its variable domains and then there are there's only one constant domain of the light chains but heavy chains have how many three or four constant domains any question after this there's no question no problem up to this now another thing that some doctors they were doing some experiment with the antibody molecules and what did they do let me tell you suppose i draw here a typical antibody molecule i hope you understand it doesn't it and what did they do that put these molecules in a flask right put the antibody molecules in flask but in the flask in this container after putting the antibody molecules i think i will make the light change color different so that you can appreciate the diagram better these are the antibody molecules which we have put into this container [Applause] and of course they are held together by yes please disulfide bonds now what this researchers did they added a very naughty type of enzyme what is this enzyme this is called papain they added a papine to this and they were surprised that papine could break down this molecule at a special points okay i'll keep my color scheme same right they found that papine could cut this molecule at this point it digested the molecule of antibody antibodies of protein that were digested by this papine and papine is a enzyme which attacked this region this is called hinge region what is this h i n g hinge region attack the hinge region and digest it from this point and this point now antibody breakdown into how many components how many fragments yes question goes to mr [Music] yes how many antibodies broken to how many components the three components look at it one component is this another component is this and another fragment is this so antibody breakdown into three fragments so what did they do they put antibody molecules into container and add the paper into that and papian digested every antibody molecule into how many fragments three fragments and these fragments which were made out of them this fragment has right amino end of the heavy chain and and complete light chain right held together another minor end of the heavy chain with complete light chain and this portion has remaining heavy chains held together by disulfide bond is that right now then after that they added the antigen to this what did they added let's suppose this is the antigen for that particular antibody they added the antigen to the solution and they came to know that these fragments antigen bind with these fragments right but do you think antigen will bind at this point or will the antigen bind here now will antigen bind here will antigen yeah will antigen bind here will antigen bind here will it bind here but it will bind here so in this way the researcher found that when antibodies are put into a container and treated by the papillion antibodies will break down into fragments some of the fragments will be binding with the antigen and other fragments will not bind with the antigen these fragments which do not bind with the antigen they found they will go to the bottom i mean bottom of the flask these molecules will these fragments will go to the bottom of the flask and there they will crystallize they will change into crystals due to that reason doctor said when an antibody is treated by the papain when an antibody molecule is again let's draw it here and here this is disulphide disulfide bond here is your light change isn't it so they found when they treat with that pain antibody will break down at this point is that right divide into three fragments out of these three fragments two fragments were able to bind with the antigens and other fragment was unable to bind with the antigen and this fragment went down and it crystallized so they called this fragment of the antibody fragment which crystallizes fc portion of the antibody in the books you very frequently read fc portion of the antibody or fc fragment of the antibody see see originally was put for the crystallization that this component of the antibody will crystallize once antibodies are treated with the papillion and this fragment this was binding with the the fragment which was antigen binding they call it fragment antigen binding so we call it fab so basically a classical molecule of antibody consists of four peptide having two heavy chains two light chains held together by disulfide bonds and having two fab fragment n1 fc fragment right or portion am i clear now actually this fc stand for crystallization but it also should remind you that with this end there is what carboxyland of the heavy chains because a minor end was here for the heavy chains so c for crystalline c for carboxyland c for complement activation some of the antibodies activate the complement this is the portion of the antibody which activate the complement this is the portion of the antibody which activate the complement it means in this domain more specifically if you remember there was for heavy chain how many domains were there heavy chain variable constant heavy chain one constant heavy chain constant heavy chain 2 and constant heavy chain 3 or some cases 4. actually this is the constant heavy chain 2 which are the capability to activate the complements so complement activating part of the antibody is part of the fc fragment so fc fragment should remind you that some of that this portion crystallizes this portion is having carboxyl end of the heavy chain and if if this antibody is going to activate the complement then fc portion will activate the complement and you will know later that igg class of the antibody crosses placenta igg class of the antibody from the mother through the placenta goes to the fetus so actually with the placental cell this portion of the antibody bind and help the antibody to cross through the placenta so it should remember remind you also about crossing cross through yes play center and you know antibodies bind with specific type of cells for example later on later on you will learn ige especially bind with the catches the mast cell is that right so again igg will igg class of antibodies will catch the mast cell bind the mass cell with this portion so catching cells am i clear no problem so fc portion stand for what originally is stranded for this fragment could crystallize but this should also remind fc stand for carboxyl and fc stands for fragment which activate complements fragment which help the antibody to cross the placenta and fragment of the antibody which helps it to bind with the cells any question up to this and fav portion it's enough to say that this is a fragment which is antigen binding fragment am i clear no problem after this okay then so we can say that antibody one antibody has one thing antibody plus pepin yes goes to what thing antibody will go into what antibody treated by the pain will go into two f a b fragment plus one fc fragment is that right now we do another treatment take an antibody molecule let's make some seductive color scheme this is right this is a typical antibody molecule of course consisting of two heavy chains and two light chains is that right now rather than papain this time we treat it by pepsin you have heard of pepsin what is pepsi it is also proteolytic enzyme not a name of a girl pepsin right uh when antibodies treated by the pepsin uh what at which point pepsin will digest the antibody it produces multiple digestions at this point so actually now when antibody is treated by the pepsin then fc portion is digested at multiple fragments but both fab portion are still kept together the important point is that pepsin attack the antibody molecule not at the hinge region rather to away from the hinge region towards the carboxyl end of the heavy chains is that right due to this reason uh both fab portion are kept together am i right now you'll help me rapidly if i say this is one antibody molecule and this is another antibody molecule let me take your test enzyme attack here and divide the antibody molecule into how many fragments three which enzyme is this yes papain and if i say that enzyme attack here and both fab portion are still held together what is this pepsi am i clear no problem up to this for sure okay so now we have learned something about basic structure of the anti-body another thing then when antibody is reacting with the antigen when antigen and antibody bind together they are held together by what type of forces and what type of bond you know when they come together they make a bond isn't it so what type of bond is present between the antibody and antigen yeah i'm about to be impressed by you okay let me make our original molecule again i hope you remember what are these chains i am drawing heavy chains and what are these chains yes light chains and rapidly tell me what are these bonds i'm making disulfide bonds that's good and what is this fragment variable of the heavy chain and this is also variable of the heavy chain and what should be here this area variable of the light chain and what should be here variable of the light chains then let's suppose i'm going to make the antigen if antigen is like this right now this antigen is going to fit here then what will happen what was this area constant or variable yes variable now when this will fit into this i think i have to make this a little lengthy so that it should look more proportionate with that yes now this is caught over here [Music] and right so we say antigen is caught it's caught in between the variable region of heavy chain and variable region of the light chain this is what you already know now i know a little more actually within the variable region there are very special areas which make the fitting of which make the fitting of variable region more better with the antigen and these areas are given an additional name you know this is making a better fit isn't it these areas are called hyper variable regions what are these called these three are called hyper variable regions so we say within the variable region of the light chain and within the variable region of the heavy chain there are small minor acid groups right which are called hyper variable regions which make the binding between the uh you can say antibody and antigen as precise as possible very very precise is that right now i will draw the same thing here and you will tell me what's going on here yes now you will tell me that this is variable of the heavy chain and this is variable of the light chain and antibody antigen is caught over right within the variable of the light chain what is this region hyper variable regions is that clear one thing which is very important to know that in a given antibody molecule the antigen will bind on the same side one side that is the same antigen is going to bind on the other side as well right so both sides have the same antigen specificity am i clear no problem up to this right then i was talking about with which forces they are held together or which type of bonds are in between them what type of bonds are in between them the forces are the forces with which antibody and antigen are interacting those forces are very simple forces these forces are yes have you heard of electrostatic forces electro static forces let me tell you how they are coming for example a minor acid which is present over here is positively charged and minus it here is negatively charged they are attracted to each attracted to each other you see they are held together by electro static forces or by the wonder wall forces you know vulnerable forces wonder wall forces so there are electrostatic forces or they are wonderful forces this wall is not that wall in which you sit and fall down right this is v so electrostatic forces and vulnerable forces keep the antigen and antibodies together when they are specific for each other and what type of bonds are formed in between is this ionic bonds or are they covalent bonds right or they are like simple hydrogen bonds and hydrophobic bonds yes yeah dr safa is trying to tell you know the bonding between the antibody and antigen is one way to tell is that is it strong bonds or weak bonds okay only tell me this thing the weak bonds right if you bring you know let's suppose if there are you bring lot of antibodies right and some of the antigens may dissociate and go to the other antibody if all the antibodies have same antigen specificity so these are these bonds are not permanent bonds they're somewhat reversible bond or they're weak bonds so we can say that these bonds are not ionic bonds these are not covalent bonds these are simply yes hydrogen bonds and hydrophobic bonds so the forces which are keeping the specific antigen antibody molecule together are vulnerable forces and electrostatic forces and making very weak bonds like hydrogen bonds and hydrophobic bonds am i clear to all of you is there any special question here there is no okay let's have a break

Channel: Dr. Najeeb Lectures

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Keywords: antibodies, antibody structure and function, antibody, igg, immunoglobulins, iga, ige, igm, igd, immune system, immunology, immunoglobulin, mast cells, antibody structure, b cells, structure of immunoglobulin, structure and function of antibodies, dr najeeb, dr najeeb lectures, medical lectures, medical videos, usmle step 1, medicine, different types of antibodies, plasma cells, igm antibody, antibody function, types of antibodies, antibodies structure, antibodies ige, antibodies types

Id: ssIBNVLSG58

Length: 49min 37sec (2977 seconds)

Published: Thu Apr 08 2021