In this video we're going to begin our discussion on antibodies. Now antibodies play a big role in immunity and for that reason, before we actually talk directly about antibodies, we're first going to do a summary on immunity to give you guys a little bit of context. Now it's important to know that organisms are continually subject to attack by pathogens that cause disease. And for that reason, it's important that organisms have a complex immune system to help defend against these pathogens that are constantly attacking. And so there are 2 general types of immunity, innate immunity, which acts as the first line of defense, and adaptive immunity, which acts as the second line of defense. Now, innate immunity, because it acts as the first line of defense, It's a more generalized nonspecific immunity that's used against all pathogens, and this includes the skin and mucus. Whereas, adaptive immunity on the other hand is a much more specific type of immunity with both an adaptive and a memory component and this includes both t cells and b cells. Now, this adaptive immunity can actually be further split into 2 types. The first is cellular immunity and the second is humoral immunity. Now, cellular immunity is primarily going to target intracellular pathogens that make their way inside of cells using t cells. And humoral immunity, on the other hand, is primarily going to target extracellular pathogens on the outside of cells using antibodies and b cells. And so really this is the first point here where we're introducing antibodies into our lesson. And so notice down below in our example, we're showing you a more visual display of the immune system summary that we described up above. And so you can see that the immune system can be split in to 2 groups, innate nonspecific immunity, which acts as the first line of defense and includes defense against all pathogens, and includes the skin, mucus, and stomach acid. And then the second type of immunity is adaptive or specific immunity, which has adaptivity and memory and acts as the second line of defense. Now, this adaptive specific immunity can be further split up into cellular immunity and humoral immunity. Now, cellular immunity is going to defend inside of the cell using t cells whereas humoral immunity is going to defend outside of the cells using B cells and antibodies. And so up above notice that we're showing you over here on the left a t cell that is going to attack intracellular pathogens. And then on the right, we're showing you a b cell, that is going to attack extra cellular pathogens outside the cells. And so you can see right here is actually the structure of an antibody. And we'll be able to talk more about antibodies in our next video. So, now that we've concluded our summary of immunity, I'll see you guys in our next video.
2
Problem
Problem
Humoral immunity refers to the part of the immune response mediated by:
A
T lymphocytes.
B
Antigens.
C
The thymus.
D
The skin.
E
Antibodies.
F
C lymphocytes.
3
concept
Antibody
Video duration:
3m
Play a video:
Video transcript
Alright. So now that we've briefly summarized immunity, in this video, we're going to talk about antibodies. Now, antibodies are also commonly referred to as just immunoglobulins and abbreviated as IG for short. And so antibodies or immunoglobulins are just y shaped proteins that can recognize and bind to an antigen's epitope. But what in the world is an antigen's epitope? Well, an antigen is really just any substance or compound that can provoke an immune response. Whereas an epitope, on the other hand, is going to be a very specific and exact binding site on the antigen that an antibody binds to. And so notice down below we're showing you a bacterial antigen right here, which would just be the entire bacteria. But, again, an antigen is any compound. So it could be a bacterial antigen or it could be a viral antigen or some other compound as well. And so notice that these specific shapes that are on the perimeter of the bacteria are representing epitopes. And so what you'll notice is that the antibody over here, this Y shaped protein, is binding specifically to this orange epitope, which is again the exact binding site on an antigen that an antibody binds to. Now antibodies have a very very strong affinity to their epitope, meaning that they have quite a low k d. And so they also will bind to the epitope via an induced fit model. Now as we mentioned in our previous lesson videos, antibodies are produced by b cells and they are part of humoral immunity for that reason. And so what you'll notice is down below, we're showing you this b cell here in blue and notice that the b cells can be physically attached to the, b cell's perimeter here embedded in the membrane of the B cell and, the antibodies can still attach and bind to their epitopes in this way. Or it's also possible that the antibodies can be secreted by the b cell, into the environment so that they are free and, dissociated from the actual b cell. And so moving forward, we'll be able to talk about, these secreted, antibodies, further. Now, it's important to note that antibodies are not only important for immunity purposes, but they can also be isolated for biochemical techniques such as Eliza's, which we'll talk more about later in our course. But for now, this is a brief introduction to antibodies and in our next video, we'll talk more about the structure of an antibody. So I'll see you guys there.
4
concept
Antibody
Video duration:
5m
Play a video:
Video transcript
So, from our last lesson video, we already know that antibodies are y shaped proteins. But in this video, we're going to talk more details about antibody structure. And so antibodies actually consist of 4 polypeptide chains, 2 of which are identical light chains or l chains for short, and the other 2 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 4 chains are covalently linked together via disulfide 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 our y shaped antibody has 4 polypeptide chains. It has this light chain that is identical to 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 in mass. And also notice that these four chains are covalently linked together via these disulfide bonds that exist between the r groups of cysteine 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 y and it contains the n terminal end of each of the polypeptide chains. So So, if we take a look down below at our image, notice that the V or variable domain is highlighted with a green background right here at the tips of the prongs of the y. And notice that it also contains the n terminal end or the free amino groups of each of the 4 polypeptide chains just like what we said up above. Now, what's also important to note is that the, V domain contains the antigen binding site. So, this is where the antibody is going to bind to the antigen at these 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 c domain on the other hand, because it's the constant domain, it's not actually going to vary. It's gonna remain constant even between different antibodies. Now the c 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 look take a look down below, of course, the c domain, is 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 antigen at these positions and then an immune system cell can bind to the c domain. And so the antibody can act as an intermediate between the immune system cell and the antigen. 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 heavy chain here and the light chain has 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 y. And so here in a dotted red line, what we have is an imaginary line if we were to break our antibody 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 FAB region and this is because this, has the, the fragment that has the antigen binding sites. 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 antibody down below, which would be the fc 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 course. So I'll see you guys in our next video.
5
Problem
Problem
What is the subunit structure of IgG, one of the 5 classes of antibodies produced by our immune system?
A
2 light chains and 2 heavy chains.
B
2 light chains, 2 heavy chains, and a J chain.
C
4 light chains, 4 heavy chains, and a J chain.
D
10 light chains, 6 heavy chains, and a J chain.
6
concept
Antibody
Video duration:
4m
Play a video:
Video transcript
In this video, we're going to talk about some antibody functions. Now antibodies have many many different types of functions so we're not gonna be able to get into all the details of all of the different types of functions. However, some of the more common functions that your professors might expect you to know include neutralizing toxins and tagging, invading pathogens for destruction by our immune cells. Now, phagocytes are specific immune cells that will engulf and neutralize pathogens that are tagged by our antibodies. And so notice down below over here on the left hand side of our image, these little red balls that we see here represent viral antigens. And so these are indeed viruses that can cause disease. Now, these little y shaped structures that we see here in black are, of course, our antibodies. And so the antibodies will bind to the viral antigen and help make it a lot easier for this phagocyte here to ingest the viral antigen and neutralize it. Now notice that these little gray balls that we see here around the phagocyte represent antibody receptors, more specifically, fc receptors. And recall from our last lesson video that the FC region is just the region of the antibody that contains the constant region. So, it's essentially the stem of the y of the antibody. And so, you can see over here that these little receptors are binding to the Fc region of the antibody and helping to make it a lot easier for this phagocyte to engulf the viral antigen. And then once the viral antigen has been engulfed, it can be destroyed and neutralized. Now over here on the right hand side, what we have are additional, mechanisms of antigen inactivation by antibody binding. So additional functions of antibodies and so, of course, antibodies can be used for neutralizing toxins and other antigens as well. So you can see, here in yellow we have a viral antigen and in red here we have this bacterial antigen And notice that our antibodies here are these y shaped structures that can bind to the antigens and essentially neutralize them. Meaning, it will, make the harmful portions of these antigens ineffective and inactivate them. Now, agglutination, we know from our previous lesson videos, is just a fancy word that means clumping. And so you can see down below because there are 2 antigen binding sites on each of these antibodies, they can actually bind to 2 separate, antigens. So here we have the bacterial antigens, and you can see that the antibody can bind to 2 separate bacterial antigens and help, clump them together. And that basically localizes these harmful bacterial antigens into one area. Again, making it easier for our immune system to, essentially, target these, antigens for destruction. And then, of course, antibodies can also be used for many different types of biochemical techniques, including antigen precipitation. And so if we had a specific antigen of interest in a solution such as this, yellow ball here and we wanted to isolate this specific antigen from the solution, we can use antibodies and the antibodies will bind to the specific antigen of interest and create a precipitate. And so, this precipitate can be, fairly easily isolated and purified. Using, a lot of the purification techniques that we talked about in our previous lesson videos. However, what you can see here, the main takeaway is that antibodies have lots and lots of different functions, but they're mainly used for immune system, destroying pathogens, and then also for biochemical techniques such as antigen precipitation, as well as, a technique that we'll talk more about later in our course called ELISA. So, we'll be able to talk more about the different classes of antibodies in our next video. So, I'll see you guys there.
7
concept
Antibody
Video duration:
4m
Play a video:
Video transcript
In this video, we're going to talk about the different antibody classes and so it turns out that there's actually 5 different classes of antibodies or in other words, 5 different classes of immunoglobulins. And so these five classes are based on differences in their heavy chains as we'll see down below in our table. And so the 5 classes of antibodies are I IgG, IgA, IgM, IgE, and IgD. And if you look at these red letters here, notice that it spells gamed, and so notice down below right here we have this antibody stick figure playing some video games, and based on his facial expression, I'd say he's pretty gamed out from playing video games for 72 hours straight. And so hopefully this antibody stick figure along with GAMED will help you guys remember the 5 different classes of antibodies. And so looking at this table right here, what I want you guys to notice is that, the light chain for all 5 classes of antibodies is exactly the same. So the light chain Y, there'd be the one that's Greek letter lambda. And so the light chain is not going to distinguish 1 antibody class from another. However, looking at the heavy chain, notice that each class of antibody has a unique heavy chain. And so it's the heavy chain that's going to distinguish 1 antibody from, one antibody class from another. And so this first row of, antibody, this first class of antibody is IgG and this is really the one that we've been talking about all along and so you can see the y shaped structure here that we talked about. Now, notice that IgE and IgD have very similar type of structures to IgG. However, IgA forms a dimer of these 2 y shaped structures and IgM tends to form a pentamer, containing 5 different y shaped structures here. Now, over here in this column, what we have is the primary feature of of these antibodies. Now, IgG is actually the most prevalent and the most abundant antibody in our blood. So this is going to be one that's involved, in protecting pretty much against all types of infections including bacterial and viral infections. Now, IgA is actually going to be highly concentrated in mucus membranes and it's going to be one that is, typically secreted by our cells and, it's also prevalent in our saliva. Now, IgM interestingly enough is usually going to be the first antibody, that's going to be produced upon infection. So, IgM is going to be the one that's going to initiate the primary immune response. So the very first immune response. And then, the common second immune response would be IgG since it's so prevalent in our blood. Now IgE on the other hand here is gonna be one that's gonna defend against allergies or allergens. And so you can see here we have a guy who's saying I'm allergic to this kitty cat right here and that's unfortunate because this is a cute little kitty cat. But IgE again is going to help defend against these allergens. Now IgD is one where its function is not really very well characterized. However, there are some, textbooks and studies that say they're involved with activating b cells and, allowing b cells to, participate in immune responses. Now over here on the far right, what we have is the distribution of these antibodies, classes throughout our bodies. And so notice that pretty much all of the antibodies are gonna be found in our bloodstreams, except for IGA, which again is gonna be highly concentrated in our mucus membrane. So it's gonna be lining our, digestive systems a lot. And so this here concludes our introduction to the antibody classes and we'll be able to talk more about antibodies as we move along in our course. So, I'll see you guys in our next video.
8
Problem
Problem
Immunoglobulin/antibody classes are distinguished by:
A
The light chains they possess.
B
Carbohydrates on their light chains.
C
Constant regions in their light chains.
D
The heavy chains they possess.
E
None are true.
9
concept
Antibody
Video duration:
2m
Play a video:
Video transcript
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 18th or 1 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 our immune system has the potential to produce. In fact, there's so many potential possibilities for antibodies that they all can be produced in one single lifetime. So, here we have a question and it's asking how in the world is it possible that antibody diversity can be so large if humans only have 25,000 genes, which is a much smaller number than 1 quintillion. And so, the answer to this question is actually right here. And so, antibody 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 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 up here has many different combinations for these different, regions of the antibody. However, through splicing and rearrangements, we can 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, antibody diversity and in our next video we'll be able to talk about monoclonal and polyclonal antibodies, so I'll see you guys there.
10
concept
Antibody
Video duration:
3m
Play a video:
Video transcript
In this video, we're going to talk about monoclonal and polyclonal antibodies and so we already know from our previous lesson videos that antibodies are important for immunity. However, also recall that antibodies are valuable reagents for biochemical assays. But in order to use antibodies in biochemical assays, we must first prepare and collect the antibodies. And so really there are 2 main types of antibody preparations that are used. The first are monoclonal antibody preparations and the second are polyclonal antibody preparations. And so these monoclonal antibodies are going to be identical antibodies. And so mono is a prefix that means 1 or singular and so these are identical antibodies and because they are identical antibodies, they're going to be specific to the same exact epitope on the same exact antigen. And monoclonal antibodies are going to be made by b cell clones and these B cell clones can be grown in cell culture in a lab. Now, polyclonal antibodies on the other hand are going to be a mixture of antibodies and so poly is a prefix that means many and so this is many different types of antibodies, a mixture of antibodies and because these are different antibodies, they're gonna be specific to different epitopes but on the same exact antigen. And so, polyclonal antibodies are gonna be made by different b cells. Now, an example of a polyclonal antibody preparation would be injecting just one single antigen into an entire animal. Well, that animal is going to have a b cell population with different b cells and those different b cells are going to produce different antibodies that are specific to different epitopes on the same single antigen that we injected. And so let's take a look down below at our example to clear some of this up and notice on the left hand side over here, we have monoclonal antibodies and on the right, what we have are polyclonal antibodies. And so notice that these yellow structures here represent the antigen, and the antigen has these different epitopes that are present on them. And so when it comes to monoclonal antibodies, these are going to be identical to each other and they're therefore going to be made by the same exact b cells. And so you can see here we have these antibodies that are identical to each other. And so, these are monoclonal antibodies. Now, polyclonal antibodies on the other hand are going to be, different. And, because they are different, they're gonna be made by different b cells. And so you can see that we have some pink antibodies different to, the triangular epitope on the same antigen. We've got these, green antibodies that are specific to to these grayish, and epitopes on the same antigen. And then, of course, we've got the blue ones as well. And so, because we have a mixture of all of these different antibodies made by different b cells that are binding to different epitopes on the same antigen, this would be a, example of polyclonal antibodies. And so that concludes our introduction to monoclonal and polyclonal antibodies, and we'll be able to get some practice utilizing these concepts as we move forward in our course. So, I'll see you guys in our next video.
11
Problem
Problem
Which of the following mechanisms is not a way that antibody diversity is attained?
A
Gene rearrangements.
B
Apoptosis.
C
Splicing.
D
Mutations.
12
Problem
Problem
What is the difference between monoclonal and polyclonal antibodies?
A
Monoclonal antibodies consist of different immunoglobulins recognizing a single epitope on different antigens, whereas polyclonal antibodies consist of different immunoglobulins recognizing many epitopes on an antigen.
B
Monoclonal antibodies are identical immunoglobulins recognizing a single epitope on different antigens, whereas polyclonal antibodies consist of many different immunoglobulins that recognize many epitopes on an antigen.
C
Monoclonal antibodies consist of different immunoglobulins recognizing a single epitope on the same antigen, whereas polyclonal antibodies consist of identical immunoglobulins recognizing many epitopes on an antigen.
D
Monoclonal antibodies are identical immunoglobulins recognizing a single epitope on the same antigen, whereas polyclonal antibodies consist of different immunoglobulins recognizing different epitopes on the same antigen.