Lecture 14 - Structure and Function of Antibodies Flashcards
Describe the structure of an antibody
(Variable domain side by side->constant domain side by side->hinge region->constant domain one on top of another) x 2
What is the heavy chain of an antibody
Inner half (variable domain->constant->hinge region->2 constant domains stacked)
What is the light chain of an antibody
outer part (variable domain->constant domain)
Five isotypes or classes of antibodies
- IgG
- IgM
- IgD
- IgE
- IgA
Where is the antigen binding site of an antibody
between the 2 variable domains on either side of an antibody
Where is the Fab region on an antibody
Diagonal piece at top
Where is the Fc region on an antibody
vertical piece at bottom
How many polypoeptide chains do an antibody have
2 heavy chains and 2 light chains
What are the different types of heavy chains
mu, delta, gamma, epsilon, alpha
What do the heavy chains determine
the isotype of antibody
Each molecule of the 2 identical light chains have either a ___ or ___
lambda or kappa (all five classes of antibodies use both kappa and lambda light chains)
What hold the chains together and are also important in the structure of the domain loops
disulfide bonds
What are domains
repeating homologous units that compose chains; composed of about 110 AA that fold into loops and held by a disulfide bond
What is Fab (fragment antigen binding)
antigen binding end of the molecule, consists of the Vh, Ch1, VL, and CL domains
What is the Fc (fragment crystallizable)
tail of the molecule, consists of CH2 and beyond
What does Fc dictate
complement fixation, opsonization, binding of mast cells
What is the antigen binding site
-consists of VH and VL domains
-binds to the epitope on the antigen
What are within the antigen binding site VH and VL domains
hypervariable regions (CDRs)
Antigen
stimulates an immune response
Epitope
part of antigen that the antibody binds to; an antigen can have many epitopes
Properties of antigen-antibody binding
- non-covalent
- electrostatic, H bonds, Van der Waals forces, hydrophobic bonds
- reversible
- goes to equilibrium
- rapid
Structure of IgG
four heavy chain domains
Where is IgG found
blood stream and interstitital fluids; high conc in colostrum of large domestic species
How much of total serum antibody does IgG make up
80% with half life of three weeks
Important functions of IgG
-complement activation
-neutralization of viruses and toxins
-opsonization
-systemic immunity in newborn
-antibody dependent cell mediated cytotoxicity
Structure of IgM
pentamer, heavy chain has 5 domains, held together by disulfide bonsd and J chain
How many identical epitopes can IgM bind
10
Where is IgM found
blood stream
What is the first class of antibody produced in primary response
IgM
Functions of IgM
- complement activation
- agglutination
Relative amounts of IgM and IgG produced during the primary and secondary immune response
IgM predominates in primary immune response, IgG predominates in a later response
Structure of IgA
4 heavy chain domains held togehter by a J chain
Where is IgA found
-mucosal surfaces
-secretory component added to molecule as it is transported to the mucosal surface
-mother’s milk
Functions of IgA
-neutralize toxins and block entry of pathogens on mucosal surfaces
-found in mother’s milk and helps provide intestinal immunity to neonate
IgE structure
-five domains in heavy chain, lot of polysaccharide attached to heavy chain
-Fc portion has high affinity for the Fc receptor on mast cell
What happens when binding of antigen to the IgE on mast cell
mast cell degranulation
What can IgE activate also
eosinophils
Where is most IgE found
mast cells, concentration in plasma is low
functions of IgE
- important in defense against helminthic parasites
- Mediator of immediate hypersensitivity
Where is IgD found
B cell surfaces
IgD function
- regulatory
- B cell development
