Antibody: Videos & Practice Problems

Antibodies, or immunoglobulins, are Y-shaped proteins crucial for the immune response, binding specifically to antigens at their epitopes. They consist of four polypeptide chains: two light chains and two heavy chains, linked by disulfide bonds. Antibodies function by neutralizing toxins, tagging pathogens for destruction, and facilitating agglutination. There are five classes of antibodies—IgG, IgA, IgM, IgE, and IgD—each with unique roles and structures. Antibody diversity arises from gene rearrangements and mutations, enabling the immune system to produce a vast array of antibodies to combat various pathogens.

Antibody

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. There are two 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.

Innate immunity, because it acts as the first line of defense, is 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 two types. The first is cellular immunity and the second is humoral immunity. 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, this is the first point here where we're introducing antibodies into our lesson.

Notice down below in our example, we're showing you a more visual display of the immune system summary that we described above. You can see that the immune system can be split into two 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. The second type of immunity is adaptive or specific immunity, which has adaptivity and memory and acts as the second line of defense. This adaptive specific immunity can be further split up into cellular immunity and humoral immunity. Cellular immunity is going to defend inside the cell using T cells, whereas humoral immunity is going to defend outside of the cells using B cells and antibodies. 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 extracellular pathogens outside the cells. You can see right here is actually the structure of an antibody. 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.

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.

Answer: (E)

Antibody

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 strong affinity to their epitope, meaning that they have quite a low kd. 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 ELISAs, 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.

Antibody

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 about antibody structure. 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. The light chains are actually much lighter than the heavy chains, which are much heavier and larger. These 4 chains are covalently linked together via disulfide bonds. If we take a look down below at our image, notice we have our Y-shaped antibody right here. 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. The heavier chains highlighted in green are much larger and therefore much heavier than the lighter chains which are much smaller and lighter in mass. Also, notice that these four chains are covalently linked together via these disulfide bonds that exist between the R groups of cysteine residues.

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. The variable region or the V domain is 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. 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. 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. The V domain contains the antigen binding site. This is where the antibody is going to bind to the antigen at these two potential positions indicated by the arrows. The reason it's called the V or variable domain is because this region will actually vary between different antibodies. The C domain, on the other hand, because it's the constant domain, isn't going to vary. It will remain constant even between different antibodies. The C domain is, of course, going to be the rest of the antibody. It's going to be located at the hinge and the stem of the Y. If we take a look down below, of course, the C domain, is the rest of the antibody here. The C domain is important because it's actually recognized by immune system cells. 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. The antibody can act as an intermediate between the immune system cell and the antigen. You'll notice in our image here, we have the V domain, here with the Vs on them and then whether or not they're light or heavy chains is indicated by the L and the H. You can see that both the heavy chain here and the light chain has as well as a constant domain. 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, we have an imaginary line if we were to break our antibody right at the hinge. 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 fragment that has the antigen binding sites. You can see we have the antigen binding site in this region. 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. This would be the FC region, right here. 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. I’ll see you guys in our next video.

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.

Answer: (A)

Antibody

In this video, we're going to talk about some antibody functions. Now antibodies have many different types of functions, so we're not going to be able to get into all the details of all 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.

Antibody

In this video, we're going to talk about the different antibody classes and so it turns out that there are 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 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 one 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 one 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 types 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 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 mucous 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. 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 going to be one that's going to 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 antibody classes throughout our bodies. And so notice that pretty much all of the antibodies are going to be found in our bloodstreams, except for IgA, which again is going to be highly concentrated in our mucous membrane. So it's going to 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.

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.

Answer: (D)

Antibody

In this video, we're going to talk about antibody diversity. It turns out that our immune systems have the potential to produce an enormous amount of different antibodies, perhaps greater than 10 18 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 are 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 it is possible that antibody diversity can be so large if humans only have 25,000 genes, which is a much smaller number than 1 quintillion. The answer to this question is actually right here. Antibody diversity results from a significant amount of gene rearrangements, splicing, and mutations. Notice, down below over here on the left-hand side, what we have is DNA being shown. This DNA is coding for an antibody. You can see that the different regions of the DNA are color-coded to show you what part of the antibody they express.

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. 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. Through all of these gene rearrangements, splicing, and mutations, we get a diverse antibody.

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.

Antibody

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 these grayish 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 an 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.

Which of the following mechanisms is not a way that antibody diversity is attained?

• A. Gene rearrangements.
• B. Apoptosis.
• C. Splicing.
• D. Mutations.

Answer: (B)

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.

Answer: (D)

Here’s what students ask on this topic:

What are the main functions of antibodies in the immune system?

Antibodies, or immunoglobulins, have several key functions in the immune system. They neutralize toxins by binding to them, preventing them from interacting with cells. They also tag pathogens for destruction, a process known as opsonization, making it easier for immune cells like phagocytes to engulf and destroy these pathogens. Additionally, antibodies facilitate agglutination, where they bind to multiple antigens, clumping them together and localizing the threat. This clumping makes it easier for the immune system to target and eliminate the pathogens. These functions are crucial for maintaining the body's defense against infections and diseases.

How do antibodies recognize and bind to specific antigens?

Antibodies recognize and bind to specific antigens through their variable regions, also known as V domains. These regions are located at the tips of the Y-shaped antibody and contain the antigen-binding sites. Each antibody has a unique V domain that is specific to a particular epitope, the exact binding site on an antigen. The binding occurs via an induced fit model, where the antibody and antigen undergo conformational changes to fit together tightly. This specificity is due to the unique amino acid sequences in the V domains, allowing antibodies to bind with high affinity to their corresponding epitopes.

What are the different classes of antibodies and their functions?

There are five classes of antibodies: IgG, IgA, IgM, IgE, and IgD. IgG is the most abundant and protects against bacterial and viral infections. IgA is found in mucous membranes and secretions like saliva, providing localized protection. IgM is the first antibody produced in response to an infection and initiates the primary immune response. IgE is involved in allergic reactions and defends against parasitic infections. IgD's function is less well understood but is believed to play a role in activating B cells. Each class has unique structural features and functions, contributing to the immune system's versatility.

How is antibody diversity generated in the immune system?

Antibody diversity is generated through a combination of gene rearrangements, splicing, and mutations. The genes encoding antibodies undergo somatic recombination, where different gene segments are shuffled and joined in various combinations. This process creates a vast array of unique antibodies. Additionally, somatic hypermutation introduces point mutations in the variable regions of antibody genes, further increasing diversity. These mechanisms enable the immune system to produce a potentially enormous number of different antibodies, estimated to be greater than 10¹⁸, allowing it to recognize and combat a wide variety of pathogens.

What is the difference between monoclonal and polyclonal antibodies?

Monoclonal antibodies are identical antibodies produced by a single clone of B cells and are specific to the same epitope on an antigen. They are generated in the lab by fusing B cells with myeloma cells to create hybridomas, which can be cultured to produce large quantities of the antibody. Polyclonal antibodies, on the other hand, are a mixture of antibodies produced by different B cells in response to an antigen. They recognize multiple epitopes on the same antigen. Polyclonal antibodies are typically generated by immunizing an animal with an antigen and then collecting the serum, which contains the diverse antibodies.