Lecture 2 Flashcards
how many genes are there in the human genome?
30000
In a heavy chain and TCRbeta what is the V region encoded by?
V, D and J segments
what segment is the largest?
V
in the light chain and TCRalpha what is the V region encoded by?
V and J
what happens when DNA is broken in B cells?
rearranged to assemble a gene that encodes for the variable region
when is DNA broken on B cells?
during development in the bone marrow
how do B cells and T cell generate random antibodies?
by randomly breaking their DNA
what are the two loci containing L chains?
lambda and kappa
where does the transcript join on the antibody?
constant region
what is the order of the B cell development for Ig arrangements?
heavy chains then light chains
what is rearranged after D-J in the heavy chain?
V-DJ
what segments rearranged first in the kappa light chain region?
V-J
what happens if the kappa arrangement is unsuccessful in the light chain?
lambda segments start to rearrange
on what chromosome is the heavy chain locus found on?
14
on what chromosome is the kappa chain locus found on?
2
on what chromosome is the lambda chain locus found on?
22
what does a D and a J segment make on a B cell?
IgM
how can IgM switch to IgG?
by class switching
explain recombination signal sequences
Ig gene segments are rearranged by special sequences flanking each of the V,D,J segments
what enzyme is involved?
V,D,J recombinase
what do RAG-1 and RAG-2 do?
they are genes that encode lymphoid-specific components of the recombinase
what do mutations of RAG genes result in?
immunodeficiency
what is light chain isotope exclusion?
each B cell expresses wither a rearranged kappa or lambda light chain NEVER both
what is each B cell compared to another B cell
unique, never the same as another
what does junctional diversity do?
increases diversity further by imprecise joining and random addition of nucleotides
what does terminal transferase do?
randomly adds in extra nucleotides
what are two other examples of mechanisms for generation of antibody diversity?
somatic hypermutation (SHM)
what does SHM occur?
in germinal centres
what is SHM performed by?
any enzyme called AID (activation-induced deaminase)
what do AIDs act on?
on DNA to de-aminate cytosine to uracil
what are the membrane and secreted forms of each B cell produced by?
alternative RNA processing
what does each secreted form made by a B cell lack?
a transmembrane region in the constant region
what is released from the B cell as a secreted product?
RNA
what heavy chain is IgM on?
Mu
what heavy chain is IgD on?
delta
what heavy chain is IgG on?
lambda
what heavy chain is IgA on?
alpha
what heavy chain is IgE on?
epsilon
what does it mean when Cdelta is next to CMu?
IgD can be co-expressed with IgM
