Lecture 6: Antibodies and Antigens Flashcards
Antibody structure
2 heavy chains
2 light chains
Chains bound together by disulfide bond & non covalent interactions
Chains have constant and variable regions
V and C regions
V region contains Ab binding site
C region determines fate of Ab
Antibody cleavage
Antibodies can be cleaved to yield two Fab fragments (Fragment Ag binding site) and an Fc fragment (responsible for effector functions)
Cleavage by papain gives
Two Fab fragments and an Fc fragment
Cleavage by pepsin
Generates single bivalent Ag binding fragment F(ab’)2
Heavy chains and their Ig’s
u (mu) - IgM S (Delta) - IgD y (gamma) - IgG e (epsilon) - IgE a (alpha) - IgA
Light chains
k (kappa)
l (lambda)
Ab unit can only have one, not both
H - L chain bonds
Both chains have intrachain disulfide bridges every 90 AAs, creating polypeptide loops
Ag binding site in secreted IgG formed by
Juxtaposition of Variable light and Variable heavy domains
Difference b/w membrane bound IgM and secreted IgG
Membrane IgM has one extra CH4 domain
Conformational determinant
Only recognizes folded, non-denatured proteins
Linear determinant
If there is an accessible linear sequence, Ig can bind determinant in native form. If not, it must be denatured
Neoantigenic determinant
Proteolysis creates a site that can be bound
Affinity of Abs formed in the primary response vs Memory response
Lower affinity in primary, higher in memory response
When is affinity critical
If Ag is toxin or Virus and must be eliminated immediately at low titers
Ab valence
Maximum number of antigenic determinants with which it can interact
IgG valence
IgG has two Fab regions and can bind two molecules of Ag - valence is 2
