#2 Antibody Structure 01.08 Flashcards
what is an Ab?
secreted version of Ig produced by a B cell
what is an Ig?
antigen binding molecule of a B cell
Ab and Ig (of the B cell receptor) are ___
identical
what is the difference between Ab and Ig?
they are the same, but…
Ab are the secreted form
Ig are the membrane bound form
Ab are produced in large quantities by
plasma cells
what are plasma cells?
fully differentiated B cells
each Ab produced by a B cell has the same/different specificity for antigen
EXACT same
B cells can become
memory cell
plasma cell
Ab are produced by
B cells
what stimulates the B cell to develop into plasma cell?
encounter with antigen
what is the sole purpose of plasma cells?
to secrete Ab
each Ab has __ light chain and __ heavy chain. each, respectively, are ___.
2 heavy
2 light
identical
B cells : ____ :: T cell : ____
heavy and light chains
beta and alpha chains
light chain is composed of how many constant and how many variable? heavy chain?
light: 1 constant, 1 variable
heavy: 1 variable, 3 constant
how many types of light and heavy chains are produced by a single B cell?
a single type for each
why is the constant region termed so?
rarely has mutations
the N-termini of the Ab is where?
antigen-binding regions are
the C-termini of the Ab is where?
the base of the Fc region
what connects the two parts of the heavy chain?
hinge region
what special trait characterizes the Fc region just below the double bond?
two heavy chains of Fc region are connected by 2 disulfide bonds
name 3 points in the Ab where diS bonds exist
- heavy-to-heavy chains in Fc region
- light-to-heavy in Fab region
- intra-chain within heavy chain and light chain Ig domains
why is the variable region termed so?
that’s where variation occurs for antigen binding
what forms the Ig domains on an Ab?
alternating beta sheets
what is similar between the light chain v and c domains?
intra-chain diS bond
alternating beta sheets/beta barrel arrangement
does the loop in the light chain c domain have affect on antigen binding? what about the loop in the v domain? why?
c: no
v: yes! hyper-variable
where is the hyper-variable region (HVR) of Ab molecule? what structure thingy is this in?
light chain v region
the loops
what occurs between hyper-variable region (HVR)?
framework regions
does the hyper-variable region (HVR) have variability in aa sequence? what about the framework region?
yes! this is how you can bind diff antigens
no. can’t tolerate changes to structure, will lose function
what is an antigen?
any molecule that is bound by an antibody/BCR or TCR
T cells will bind only
linear peptides/epitopes
Ab binding is ___ and :: reversible/not reversible
covalent
reversible
the higher the binding strength/affinity of an Ab…
the longer the antigen will remain covalently bound
what 4 interactions mediate Ab binding?
- electrostatic forces
- hydrophobic interactions
- Van Der Waals
- H bonding
Ab can bind to
native or denatured proteins (unless discontinuous epitope) peptides carbs nucleic acids sm molecules and chem soluable or particulate antigens
linear epitope v. discontinuous epitope
linear: aa string in a row
discon: formed by 2* or 3* structure of protein :: if protein denatured, can’t bind
most antigens are ___ antigens
multivalent
what is a multivalent antigen?
antigen has multiple epitopes/binding areas
can an antigen have different epitopes/determinants on it ?
yes :: each bound by diff Ab
what is a determinant?
portion of antigen that Ab binds, same as epitope
what serves as a bridge between the innate and acquired immune systems?
secreted Ab
what are the 2 roles of Ab in immune response?
- opsonization + sensitization
2. neutralization
what is opsonization?
marking microbes for destruction by phagocytes
what is ADCC?
NK cells Ab dependent cell mediated cytotoxicity
name the 5 isotypes of Ab
IgG IgA IgM IgD IgE
which Ab have 3 constant regions + 1 hinge region?
“GDA” (GD Assholes):
IgG
IgD
IgA
which Ab have 4 constant regions + 0 hinge regions?
“ME”:
IgM
IgE
which Ab has subtypes? how many? why do they differ?
- IgG
- 4 subtypes
- hinge region structure is different :: varying amounts of diS bonds
which 2 Ab have subtypes?
IgG
IgA
each Ab produced by a B cell has the ___ antigen ___
EXACT SAME
specificity
can a B cell be signaled to produce a diff Ab isotype?
yes
this is called Isotype Switching
what region is altered in isotype switching? what is not altered?
- only the constant region
- specificity
what Ab can be excreted as multimers?
IgA
IgM
which Ab is ALWAYS secreted as a multimer? which has the option?
always: IgM, pentameric
optional: IgA, dimeric
what joins a multimeric Ab together?
J chain
what is the special catch about IgM’s multimeric v. monomeric forms?
monomeric: in membrane of cell, 2 binding domains
multimeric: when secreted, 10 binding domains (ALL IDENTICAL)
which Ab has the highest molecular weight? why?
IgM
because it is secreted as a pentamer
what Ab is associated with mucosa?
(dimeric) IgA
what Ab has longest half life?
IgG
what Ab is most important in B cell immune response?
IgG
what Ab has the highest concentration in serum, i.e., is most abundant?
IgG
what Ab has a serum level of 0 and is hardly ever secreted?
IgD
what Ab has a deceptively low serum concentration? why?
IgE
because it is bound by mast cells
what Abs are responsible for neutralization?
IgA
IgG
what Ab are responsible for opsonization and sensitization (for NK cell ADCC)?
IgG
specifically, IgG1 + IgG3
what is sensitization?
prepping for NK cells’ ADCC
what Ab is responsible for the sensitization of mast cells?
IgE
this is it’s only job!
what Ab is found in mucosal secretions? give example.
IgA
breast milk
what Ab is the most efficient activator od the complement cascade?
IgM
what Ab can diffuse into extravascular sites?
IgG
what Ab can transport across the placenta? what does this mean?
IgG
specifically, IgG1> IgG3, IgG4
that it is found in newborns
which Abs protect newborns? how?
IgG: placental barrier
IgA: breast milk
what is the function of the Fc region?
to bind:
- complement proteins
- Fc receptors
what is the function of the Fab region?
to bind antigens
what part of the Ab contains the variable region?
Fab
what enzyme cleaves the 2 Fab regions from the Fc region?
papain
what Ab is the most efficient activator od the complement cascade?
IgM
what Ab can diffuse into extravascular sites?
IgG
what Ab can transport across the placenta? what does this mean?
IgG
specifically, IgG1> IgG3, IgG4
that it is found in newborns
which Ab is found in newborns?
IgG
what is the function of the Fc region?
to bind:
- complement proteins
- Fc receptors
what is the function of the Fab region?
to bind antigens
what part of the Ab contains the variable region?
Fab
what enzyme cleaves the 2 Fab regions from the Fc region?
papain
