Ig genes 2 Flashcards
what kind of antibodies does the following produce
immature B cell
mature B cell
memory B cell
plasma Cell
secreted or membrane bound?
immature B cell –> can only produce MB IgM
mature B cell –> can only produce MB IgM and IgD
memory B cell –>MB GAMED
plasma Cell –> secretory GAMED depending on specialization
What two antibodies are made without constant segment gene rearrangements?
IgM and IgD
t or false, in a mature B cell IgM and IgD are made simultaneously
true
What is differential RNA splicing
this permits IgM and IgD to be made simultaneously within a cell. After DNA VDJ rearrangements, if the antibody is going to be M or D the gene gets transcribed there and then. After, RNA splicing occurs randomly to excise out either the IgD portion or IgM portion.
what are the M1 and M2 segments of constant regions?
these are membrane exons. When these are included within the transcript the antibody will be membrane bound such as in mature B cells.
What are poly-adenylation sites on constant regions of a gene?
after every constant gene region (for GAMED) there are two poly A sites where cleaving can occur.
Poly A site 1 –> occurs right after the gene for conserved regions
Poly A site 2 –> after poly A site one and includes M1 nad M2 membrane exons
how do we create a membrane bound IgM antibody?
IgM –> the VDJ—-constant regions M,D,etc. gets transcribed. then the transcript undergoes differential mRNA splicing where it is cleaved at poly-A site 2!! This includes the M1 and M2 exons which causes this antibody to be membrane bound.
how do we create a membrane bound IgD antibody?
To make an IgD antibody membrane bound; differential splicing cleaves at poly A site 4.
how do we create secretory IgM and IgD
plasma cell: differential splicing occurs at
IgM –> poly A site one (membrane exons excluded)
IgD –> poly A site 3 (“”)
true or false, to make a membrane bound antibody for any of the 5 antibodies known we must cleave at the poly A site 2.
false, this is true for all antibodies except for IgD which must be cleaved at site 4.
where do naive B cells cleave? plasma cells?
naive = MB = poly A site 2 and 4 plasma = secretory = Poly A site 1 and 3
what enzyme facilitates class switching?
AID –> activation induced cytidine.
class switching = DNA rearrangements to make other antibody constant regions
explain how class switching works starting from heavy chain VDJ rearrangement.
- heavy chain undergoes two rearrangements to form VDJ
- the first antibody to be made would be IgM and then IgD –> these are produced and are MB
- antigen binds a MB antibody
- signals tell the cell to make a specific antibody. call it IgE
- switch sequence of IgE loops around and connects to the switch sequence of IgM. This loop is cleaved (i.e. IgM gene and any genes prior to IgE gene are cleaved).
- now IgE gene is directly downstream from VDJ
- RNA processing
true or false, we can make IgM from IgA
false. Only down stream class switching can occur.
antibody diversity:
multiple germ line genes?
stating there are many genes to choose form –> many variable genes, many diversity genes, etc.
antibody diversity:
combinatorial diversity?
explains that the combination of D to J and V to DJ and V to J (light chain) contributes to diversity.
antibody diversity: junctional diversity
- junctional flexibility / RSS cleavage?
antibodies become more diverse when they are cut by Rag 1 and 2 enzymes in different nucleotide locations at RSS sequences. Differing by one or two nucleotides may affects the Ag binding region.
antibody diversity: junctional diversity
- P-nucleotide addition
p = palindromic
once Rag cuts between V and J regions or D and J regions or etc. DNA repair must occur.
P- addition adds a palindromic sequence
antibody diversity: junctional diversity
- N-nucleotide addition
TdT enzyme randomly adds nucleotides to cut region after RSS is been cleaved.
antibody diversity:
somatic hypermutation?
random point mutations occurring at hyper-variable regions (occur 100,000 times more here then anywhere else).
AID enzyme creates knicks in DNA for class switching but also sometimes creates knicks in hyper-variable regions which leads to hypermutations.
what is affinity maturation and what causes it?
increase in AB affinity for an Ag. –> caused by somatic hypermutation.
antibody diversity:
combinatorial association of H and L
refers to genetic diversity of combining light and heavy chains
