Antibody Flashcards
(26 cards)
What is the V region in an antibody?
The V (variable) region is the N-terminal portion of the antibody’s heavy or light chain, responsible for antigen binding.
Is the V region the same as the V domain?
Yes, the V domain refers to the folded domain formed by the V region sequence, which binds antigen.
What are hypervariable regions in antibodies?
They are three short, highly variable sequences in the V region that determine antigen specificity.
What are CDRs?
Complementarity-determining regions; another term for hypervariable regions that contact the antigen.
How many CDRs are there per antibody chain?
Three per chain (CDR1, CDR2, and CDR3 for both VH and VL).
Which CDR is the most variable?
CDR3 is the most variable among the three CDRs.
How do CDRs form the antigen-binding site?
Three CDRs from the heavy chain and three from the light chain form the antigen-binding surface.
What are framework regions?
More conserved regions in the V domain that support and stabilize the CDR loops.
Do framework regions contact antigen?
Sometimes, though CDRs form most contacts, framework regions may also bind antigen.
What determines the class (isotype) of an antibody?
The structure of the heavy chain C (constant) region.
Name the five major antibody isotypes.
IgA, IgD, IgE, IgG, and IgM.
Which isotypes are subdivided into subtypes?
IgA (IgA1, IgA2) and IgG (IgG1 to IgG4).
What do different isotypes bind to for effector function?
Fc receptors on immune cells and complement proteins.
How many CH domains do IgG, IgA, and IgD have?
Three CH domains.
How many CH domains do IgM and IgE have?
Four CH domains.
What is the hinge region?
A flexible segment between CH1 and CH2 that allows antibody arms to move.
What are the two light chain isotypes?
κ (kappa) and λ (lambda).
Can an antibody have both κ and λ chains?
No, each antibody has either two κ or two λ chains, never one of each.
What is the clinical use of κ/λ ratio?
Abnormal ratios can indicate B cell lymphomas.
What differs between secreted and membrane antibodies?
Their C-terminal regions—secreted forms have a tail piece; membrane-bound forms have a transmembrane region.
What helps membrane antibodies anchor to the membrane?
A positively charged juxtamembrane region that binds membrane phospholipids.
Which antibody isotypes form multimers?
Secreted IgM (pentamer/hexamer) and IgA (dimer).
What is the J chain?
A small polypeptide that joins IgA and IgM monomers into multimers.
Does the J chain come from the antibody gene?
No, it is a separate protein expressed in plasma cells.
