Biochem - Ch 15 - Antibodies
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What are antibodies produced by and what are they?
Antibodies are glycoproteins produced and secreted by B lymphocytes (B cells).
Each antibody recognizes a specific antigen unique to its target.
Antibodies protect organisms from foreign objects by binding specific antigens, which causes clumping of particles and precipitation of antibody-antigen products. The antigen-antibody associates are then removed by macrophages.
In addition, antibodies can block viral receptors and stimulate other immune responses.
What are the five classes of immunoglobulins?
- IgA - Found in intestinal tract. By binding to specific antigenic sites of pathogens, they prevent pathogens from attaching to epithelial surfices
- IgD - Not clear.
- IgE - Protects against parasites
- IgG - Most commonly occuring immunoglobin both in blood and the extravascular fluid. Responsible for the secondary immune response.
- IgM - First immunoglobin to be secreted in response to an antigen. Most effective against microorganisms
What is the function of IgM? What is the mass?
IgM - First immunoglobin to be secreted in response to an antigen. Most effective against microorganisms
Mass of 950kD
What is the function of IgE? What is the mass?
IgE - Protects against parasites
Mass of 190kD
What is the function of IgA? What is the mass?
IgA - Found in intestinal tract. By binding to specific antigenic sites of pathogens, they prevent pathogens from attaching to epithelial surfices
Mass of 360-720kD
What is the function of IgD? What is the mass?
Mass of 160kD
What is the function of IgG? What is the mass?
IgG - Most commonly occuring immunoglobin both in blood and the extravascular fluid. Responsible for the secondary immune response.
Mass of 150kD
All immunogloblins share the common architecture of a tetrameric subunit that contains two ~23-kD _________ and two ~53 to 75-kD _________.
Light Chains and Heavy Chains.
How many S-S bounds are there between the L and H- chains in IgG?
- There are a total of 4 disulfide bonds.
Where are the variable and constant regions in IgG?
The variable regions are located towards the top two tips of the Y region and the constant region continues down from the hinge to the bottom of the Y.
Where can immunoglobins be cleaved with a proteolytic enzyme paptin into the three fragments?
In the hinge region on the heavy chains.
What is the characteristic three-dimensional struction that immunoglobulins have called? What is it composed of?
What do the hypervariable amino acid sequences determine?
Immunoglobulin fold. It is composed of three- and four-stranded antiparallel B-sheets.
The loops connecting B-strands in the variable domain of immunogloulins contain hypervariable amino acid sequences, which determine the specificity of antibody-antigen interactions.
How do antigens achieve the specificity required of antibodies?
They contain highly variable amino acid sequences. The hypervariable loops of variable domains are known as paratopes.
What are paratopes?
The hypervariable loops of variable domains on antigens. It is located towards the tip of the antibody and is composed of the highly variable amino acid sequences.
This is where the antigen binds to the antibody.
What are epitopes?
A antigenic determinant where the antibody recognizes and binds to the antigen.
An antigen may have several locations for this allow for different antibodies to bind to them.
What type of bonding is involved in antibody-antigen binding?
Hydrogen bonding, hydrophobic, ionic, and van der Waals interactions.
(T/F) Antigens only have one epitopes on the surface.
False. Antigens may have several locations that may be recognized by antibodies.
What is an autoimmune disease?
In autoimmune disease, the body's tissues are the subject of attack by the body's immune system.
What are two characteristics of antibodies that are extremely attractive for laboratory use?
1) Extremely high specificity
2) Ability to confer recognition of foreign antigen in blood long after first activation
What cells produce antibodies?
What is the Western Blot Technique? What does it involve?
- A technique to identify specific proteins.
- It involved the use of primary antibodies specific to the protein of interest.
Secondary antibodies are used with chemical or enzymatic labels.
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