Ch.4 Ab structure & B-cell diversity Flashcards
resting b cell
has membrane bound Ig
stimulated b cell
b cell activated by Ag gives rise to Ab secreting plasma cells
Ab structure
2Fab fragments
4Fc fragment
Fab
ag binding fragment bind to exact same molecule
Fc
crystallizable fragment. constant region made of only one protein, part of H chain
hinge region
allows for flexibility of atoms (Fab)
epitope
antigenic determinant- small part of ag that fits into ag binding site of ab molecule
affinity
strength binding between receptor and ligand
avidity
strength of binding when more than one receptor is binding to the same molecule
valency
number of binding sites
ab binding sites
2- divalent
T cell receptor binding sites
1- monovalent
polyvalent
more than two binding sites
constant region
determines class and effector function
effector function
how ab removes the antigen
class/isotype
group ab with same constant region
H chain of IgG
gamma
H chain of IgM
mu
H chain of IgD
delta
H chain of IgA
alpha
H chain of IgE
epsilon
light chain constant region
lambda or kappa doesn’t influence effector function or name of ab
Ig domain
origional gene replicated many times and is used in many membrane receptors
Ig domain compostition
110 amino acids long
2 beta pleated sheets
1 intrachain disulfide bond
Ig loops/HV/CDR
extend from end of variable region where ab binds to ag.
hypervariable regions (HV)
have sequence of high variability in the amino acid sequence and DNA
framework regions
relatively conserved b/c necessary for folding. part of V region
complementary determining regions (CDR)
part of V region where ab comes into contact w/ag and binds to it
naive cell composition
IgM and IgD
IgM and IgD in naive cell
have different constant regions but same variable. Can become a memory cell with a different class but same v region
germline DNA
as found in germ cells (sperm and egg). DNA inherited on chromosome
sperm and egg produced by
meiosis-synapse- can have cross over and DNA exchange
recombination
DNA exchange
somatic cell
every cell that isn’t a germline cell
somatic recombination
rearrangement/splicing of DNA in somatic cell (only occurs in Ig and TCR DNA)
proteins (enzyme complex) that perform somatic recombination
recombination activating genes (RAG) produce RAG proteins. RAG only found in B & T cells
steps somatic recombination in B&T cells
1) RAG binds to Rss
2) RAG brings 2 Rss together forming a loop
3) intervening between 2Rss is cut out and destroyed (DNA splicing and rearrangement)
4) p&h nucleotides formed on cut ends
5) DNA repair forms coding joint
class switch
permanent change in DNA (can’t remake any spliced out C regions)
for class switch to occur
- cell must respond to ag
- must receive T cell help (T cell signals cytokines)
- ag must be a protein
production IgM and IgD requires
differential RNA splicing
co receptor
any molecule needed for ag receptor to produce a signal transduction cascade
allelic exclusion
during somatic recombination only one H and L can be used to make ab—only one ag binding site per cell (many identical copies)
Somatic hyper mutation definition
mechanisms for increasing diversity
somatic hyper mutation parameters
1) occurs after ag binding
2) only in B cells
3) only w/T cell help
4) only happens w/protein ag
point mutations
one nucleotide is changed in v region of Ig that occurs at accelerated rate
activation induced deaminase (AID)
enzyme that removes amino group from cytidine and is only active when bound to ag
