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Antibodies

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Biology

Antibodies are a type of protein called immunoglobulins, used in the body’s immune response. Antibodies are specific to complementary antigens on the cell surface membrane of non-self materials in the body, such as pathogens, toxins, and pollen.

Antibodies bind to these antigens, preparing cells and particles for destruction via phagocytosis.

How are antibodies produced?

Antibodies are produced by white blood cells called B lymphocytes (or B cells).

There are millions of different types of B cells in the body. Each cell produces one specific type of antibody, producing clones of identical antibodies. These are known as monoclonal antibodies because they are all the same.

The structure of an antibody

Antibodies are globular glycoproteins; they have a quaternary structure made up of four chains. Two of the chains are longer and called heavy chains. Two are shorter and called light chains.

Globular proteins: Spherical proteins that are somewhat water-soluble by forming colloids in water. They are one of the most common proteins.

Glycoproteins: proteins with a sugar attached.

Antibodies have a constant and variable region. The variable region is named that because it varies depending on the specific complementary antigen it binds with, while the lower constant region stays the same. The variable region includes the ends of both the light and heavy chains.

The antigen-binding site is found at the end of the variable region. The constant region binds to receptors on cells such as B cells. The four chains are connected by disulfide bridges.

Antibodies structure of an antibody StudySmarterFigure 1. Structure of an antibody. Source: Je at uwo via Wikimedia Commons.

The importance of antibody structure

The structure of an antibody is important in shaping how antibodies function. Arguably, the most important part of any antibody is the antigen-binding site. This binding site has a highly specific 3-D structure. Because antibodies are proteins, they are able to form very specific shapes, which allows them to bind specifically only to complementary antigens. This means that antibodies can be specifically targeted at certain types of cells and pathogens.

Antibodies specific antigens binding to their complimentary sites on the antibody StudySmarterFigure 2. Specific antigens binding to their complementary sites on the antibody. Source: Fvasconellos via Wikimedia Commons.

The characteristic 'Y' shape is also important. As you will see later, the structure of two binding sites instead of one allows antibodies to bind to two different antigens at once. This is important because it allows antibodies to effectively 'clump' together pathogens and other particles.

The antigen-antibody complex

Antibodies bind to antigens via the specific binding sites found on the ends of the variable region. Each binding site is made up of a sequence of amino acids that form a specific 3-D shape. This shape is complementary to a specific antigen. When an antibody and antigen bind together they form what is known as an antigen-antibody complex.

Antibodies antigen antibody complex StudySmarterFigure 2. The antigen-antibody complex. Source: Alejandro Porto, CC BY-SA 4.0, via Wikimedia Commons.

How do antibodies work?

Antibodies do not destroy pathogens and their antigens directly. Instead, they prepare antigens for destruction by phagocytes. Phagocytes are white blood cells that engulf and digest pathogens as part of the immune response. Antibodies make it easier for cell-destroying defense mechanisms to find and destroy pathogens. Antibodies have two main methods of doing this:

Agglutination

One method is agglutination.

Agglutination: Antibodies bind to multiple antigens, forming a large clump of cells or particles.

Antibodies can bind to two different pathogen antigens at once because antibodies have two binding sites. By clumping together multiple pathogens, antibodies make it easier for phagocytes to engulf and destroy pathogens in phagocytosis as all the antigens are in one centralized place.

Antibodies agglutination of antigens StudySmarterFigure 3. The agglutination of antigens. Source: OpenStax College, CC BY-SA 4.0, via Wikimedia Commons.

Marking

Following agglutination, antibodies can act as chemical markers that stimulate phagocytes to move towards the clump of antibodies and antigens. Phagocytes can then engulf the clump of pathogens and destroy them in phagocytosis.

Antibodies and toxins

Antibodies have another role in the immune system, apart from binding to antigens. Antibodies are also able to bind to toxins produced by certain pathogens. When the toxin-antibody complex is formed, the toxin is neutralised, meaning that it cannot cause harm to the body. Following this, the toxin-antibody complex can be removed by phagocytes via phagocytosis.

Phagocytosis: ingestion and elimination of particles in the cells that are larger than 0.5 .

Monoclonal antibodies

Monoclonal antibodies are a specific, single type of antibody.

The prefix 'mono-' means 'one' and the ending 'clonal' indicates that each antibody is a clone of the other. They are all the same. Scientists can clone B cells to produce large quantities of monoclonal antibodies, where each antibody is produced from copies of the same cell.

Monoclonal antibodies are becoming increasingly useful in science and medicine. They can be used to diagnose and treat different conditions and diseases.

An example of this is the use of monoclonal antibodies to treat cancer. Monoclonal antibodies bind directly to cancerous cells, either delivering targeted medication to cells (which is attached to the monoclonal antibodies) or directly blocking chemical signals that help promote cancerous growth.

Monoclonal antibodies are also useful in diagnosing different diseases. Monoclonal antibodies are used in the ELISA test, which is used to diagnose a broad range of diseases, including HIV. A step-by-step overview of the ELISA test and its use of monoclonal antibodies can be found in our article on HIV.

Antibodies - key takeaways

  • Antibodies are a specific type of protein synthesized by B cells and plasma cells in the body's immune response.
  • Antibodies bind to complementary antigens on the cell surface of non-self material and cancerous cells in the body. When antibodies bind to antigens this forms an antigen-antibody complex.
  • Antibodies have a quaternary structure made up of four chains, two longer 'heavy chains' and two shorter 'light chains'. In this structure, there is a constant region which is the same for all antibodies, and a variable region, which is specific to each different type of antibody. At the end of the variable region is the antigen-binding site, which includes the ends of both the light and heavy chains. There are two binding sites on each antibody.
  • Antibodies have a quaternary structure made up of four chains, two longer 'heavy chains' and two shorter 'light chains'. In this structure, there is a constant region which is the same for all antibodies, and a variable region, which is specific to each different type of antibody. At the end of the variable region is the antigen-binding site, which includes the ends of both the light and heavy chains. There are two binding sites on each antibody.

Antibodies

An antibody is a specific type of protein produced by B cells and plasma cells in the humoral immune response. Antibodies bind to specific foreign antigens to prepare them for destruction via phagocytosis.

Antibodies bind to specific foreign antigens. Because antibodies have two binding sites, they can bind to multiple antigens at once, causing agglutination (clumping together) of cells and particles. Antibodies also bind to some toxins produced by pathogens, neutralizing them so that they cannot cause harm to the body's cells.

 Antibodies are produced in response to the presence of non-self antigens being detected by T lymphocytes in the body. This may be caused by infection with a virus or bacteria, or the inhalation of pollen, for example.

Monoclonal antibodies are produced by a singular B cell so that each antibody is identical, while polyclonal antibodies are produced by several different immune cells, and are not all identical.

 Monoclonal antibodies are produced by B cells. They can be manufactured for medical use using mice. In this method, mice are exposed to the non-self material against which an antibody is required, causing the mouses' B cells to produce antibodies. These B cells are then fused with cancer cells so that they divide rapidly, forming what is known as hybridoma cells, from which antibodies can be extracted.

Final Antibodies Quiz

Question

What type of molecule is an antibody?

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Answer

An antibody is a protein, specifically an immunoglobulin or globular glycoprotein.

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Question

How are antibodies produced?

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Answer

Antibodies are synthesized by B cells and plasma cells in the humoral immune response. They are synthesized in response to the presence of non-self material in the body, such as a pathogen or pollen.

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Question

What is the structure of an antibody?


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Answer

An antibody is made up of four chains, two shorter light chains ad two longer heavy chains. These chains are connected by disulfide bridges. The variable region of the antibody is found at the top of the Y shape, and the constant region is found at the button of the Y shape.

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Question

Where is the antigen-binding site on an antibody?


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Answer

The antigen-binding site is found at the two ends of the antibody’s Y shape, at the end of the variable region. The antigen-binding site is located at the ends of both the light and the heavy chains.

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Why are the variable and constant regions named as they are?


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Answer

The constant region is called constant because it is the same on every antibody, while the variable region is called variable because it has a specific shape that changes depending on the cell that has produced it.

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Question

What is agglutination?


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Answer

Agglutination is when antibodies bind to multiple antigens, causing non-self cells or particles to clump together in one place. This makes it easier for phagocytes to engulf and destroy foreign material as they are all in one centralized place.

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Question

How do antibodies neutralise toxins?


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Answer

Antibodies can neutralize some toxins by binding to them. This forms an antibody-toxin complex.

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What is the antigen-antibody complex?


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Answer

The antigen-antibody complex is the name given to when an antibody binds to a specific complementary antigen.

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How do antibodies stimulate phagocytosis?


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Answer

Antibodies can act as chemical markers which stimulate phagocytes to move towards them and the agglutinated antigens.

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Question

How does the structure of an antibody make agglutination possible?


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Answer

Antibodies have two antigen-binding sites rather than one. This means antibodies can attach to two antigens at once, so can hold two cells or particles together at once.

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Question

What are monoclonal antibodies?


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Answer

Monoclonal antibodies are a specific, single type of antibody, where all antibodies are identical to one another. This is because they are clones of one another and are produced by the same B cell.

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Question

What are the uses of monoclonal antibodies?


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Answer

Monoclonal antibodies can be used to treat diseases such as cancer. They can also be used to diagnose diseases or conditions, such as HIV.

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Question

How can monoclonal antibodies be used to treat cancer?


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Answer

Monoclonal antibodies can bind directly to specific cancerous cells. Once bound, they can either act directly by blocking chemical signals that promote cancerous growth or deliver targeted medication attached to the antibodies.

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Question

How can monoclonal antibodies be used for diagnosing diseases?


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Answer

Monoclonal antibodies are used in the ELISA test, which can diagnose a range of diseases, including HIV.

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Question

What are the 3 main functions of antibodies?

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Answer

Agglutination, marking and toxin neutralisation. 

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