Antibodies Flashcards
What type of molecule is an antibody/immunoglobulin?
glycoprotein
What are 3 functions of antibodies?
- complement activation (IgM + IgG)
- Opsonisation
- Cell activation via specific antibody binding receptors - Fc receptors
What is the basic structure of immunoglobulins?
- 2 light (25kDa) chains, 2 heavy (50kDa) chains
- each chain has amino and carboxyl terminal
- chains held together by disulphide bridges
What type of bonds hold immunoglobulin chains together?
disulphide bonds
What is the order of amounts of the globulins found in serum in decreasing order?
A, γ, α, β
What allows flexibility of immunoglobulins?
there is a hinge in the antibody which allows flexibility between the two Fab
What is the benefit of immunoglobulins having flexibility?
- allows angle between the two antigen binding sites to change angle depending on the proximity of cell surface determinants (how cloes together the antigens are)
Label the antigen binding sites + variable + constant regions of the light and heavy chains on the diagram.
How are the variable and light chains divided in immunoglobulins?
both light and heavy chains can be divided into variable (where the sequences are different) and constant (same sequence) regions
Where are the disulphide bonds located within the immunoglobulins?
each domain e.g. variable light, has intramolecular disulphide bonds to maintain their specific 3D structure required for antigen binding
Which region of immunoglobulins binds to cells and what does this result in?
- constant region binds to Fc receptors
- can lead to cell activation e.g. NK cells (secondary effector functions in immune response)
How many hypervariable regions exist on each antibody binding site of each immunoglobulins?
3 hypervariable regions
What is another name for the 3 hypervariable regions?
complementarity determining regions (CDRs)
What is the role of the hypervariable regions at each antigen binding site?
highly specific region, significant number of interactinos between the antibody and antigen surface
What are 4 forces involved with antibody binding?
- hydrogen bonds
- ionic bonds
- hydrophobic interactions
- van der Waals interactions
What are 4 forces involved with antibody binding?
- hydrogen bonds
- ionic bonds
- hydrophobic interactions
- van der Waals interactions
What creates high affinity bonding between antigen and antibody?
non-covalent bonds are relatively weak - to have hihg affinity must only be short distance between antigen + antibody, highly complimentary, and significant number of interactinos
What creates high affinity bonding between antigen and antibody?
non-covalent bonds are relatively weak - to have hihg affinity must only be short distance between antigen + antibody, highly complimentary, and significant number of interactinos
What is the calaculation used to work out antibody affinity for a single antigen binding site and a single epitope on the antigen?
What is antibody affinity avidity?
- Affinity = The strength of the total non-covalent interactions between a single antigen binding site and a single epitope on the antigen.
- Avidity = The overall strength of multiple interactions between an antibody with multiple binding sites and a complex antigen with multiple epitopes
What are 2 examples of cross-reactivity with antibodies?
- vaccination with cowpox induced abs to smallpox
- antibodies against microbial agents can cross react with ABO blood group antigens
What are antibody isotypes vs allotypes?
- isotypes = antibodies present in everybody with a constant region
- allotypes = antibodies that contain single amino acid mutations, giving allelic polymorphisms which vary in the population
How many heavy chain domains are there in each of the antibody classes?
- IgG: 3
- IgA: 3
- IgM: 4
- IgD: 3
- IgE: 4
What is the heavy chain globulin class for each of the antibody classes?
- IgG: γ
- IgA: α
- IgM: µ
- IgD: δ
- IgE: ε
