L02

Question 1

what gene segments encode the V region in H chain and TCR beta

Answer 1

V, D and J (V is the biggest)

Question 2

what gene segments encode the V region in L chain and TCR alpha

Answer 2

V and J

Question 3

In B cells (during their development in the bone marrow) the DNA containing the Ig gene segments is deliberately broken and the gene segments are rearranged (joined together) to form functional Ig genes

Answer 3

True

Question 4

different rearrangement for each B cell (random breakage and rearrangement)

Answer 4

True

Question 5

After DNA breakage what gene segments are joined in the light chain to encode the V region

Answer 5

single V and a single J

Question 6

what 2 loci contain L chain genes

Answer 6

κ and λ

Question 7

After DNA breakage what gene segments are joined in the H chain to encode the V region

Answer 7

V D and J

Question 8

what is the order of ig rearrangements during B cell development

Answer 8

first H chain gene segments rearrange (D-J, then V-DJ (greater variability in H chain as V, D and J segments)

then light chain gene segments rearrange: κ segments (V-J) first

if κ rearrangement is unsuccessful, then  gene segments (V-J) rearrange

Question 9

how many gene segments are there for each chain

Answer 9

check slide 16 of the lecture

Question 10

where is the H chain locus

Answer 10

chromosome 14

Question 11

where is the κ chain locus

Answer 11

chromosome 2

Question 12

where is the λ chain locus

Answer 12

chromosome 22

Question 13

what are the steps for the somatic recombination process

Answer 13

Somatic recombination is the process where DNA is cut to join immunoglobulin genes together

RAG 1 and RAG 2 protein complexes bind to RSS and cut the genes removing RSS sites

Artemis, DNA-PK, Ku, and DNA Ligase + XRCC4 form a complex that binds the RAG proteins joining RSS into the signal joint

Hair pins at the end of the gene segments are cleaved and TdT adds additional nucleotides to the DNA strand and the other enzymes ligate the ends together

Question 14

in each individual B cell, only one rearranged H chain gene from one chromosome (i.e. allele) is expressed

Answer 14

True

Question 15

more than one rearranged L chain from one chromosome is expressed by each individual B cell

Answer 15

False

Question 16

each B cell expresses either a rearranged kappa or lamda light chain; never both

Answer 16

True

Question 17

what is combinatorial diversity

Answer 17

different V, D and J segments recombine to produce different sequences

Question 18

what is junctional diversity

Answer 18

imprecise joining (small differences in sequences where V-D and D-J segments join)

N regions (random addition of nucleotides at junctions of V-D and D-J by terminal transferase)

Question 19

what are the features of somatic hypermutation (SHM)

Answer 19

mutation frequency in antibody (H/L) V genes is orders of magnitude higher than that seen in all other areas of the genome

SHM occurs in germinal centres (GC) as B cells recognize Ag and proliferate/become activated

Question 20

which enzyme performs SHM

Answer 20

activation-induced deaminase (AID)

Question 21

how does activation-induced deaminase (AID)
work

Answer 21

AID acts on DNA to de-aminate cytosine to uracil

uracil is then recognized by error-prone DNA repair pathways leading to mutations

Question 22

the membrane and secreted forms of BCR are produced by alternative RNA processing

Answer 22

true

Question 23

what is the heavy chain C region gene for each Ig class

Answer 23

IgM —μ

IgD — δ

IgG — γ

IgA — α

IgE — ε

Question 24

four γ chain gene segments correspond to the four IgG subclasses; similarly two α chain gene segments

Answer 24

True

Question 25

which class is the first expressed in B cells

Answer 25

IgM

Question 26

why is IgM the first class expressed in B cells

Answer 26

the Cμ segment is physically closest to the V, D and J gene segments

Question 27

why can IgD be co expressed with IgM

Answer 27

Cδ is next to Cμ

Question 28

how is IgD and IgM co expressed

Answer 28

differential processing of the RNA from the two C region genes

Question 29

what does switching to different Ig classes require

Answer 29

further DNA recombination: guided by switch regions involving the enzyme AID

Question 30

what steps insure AB diversity

Answer 30

there are multiple gene segments for each chain

combinatorial diversity

combinations of heavy and light chains

junctional diversity increases diversity further

somatic hypermutation (SHM)

Question 31

how many possible light chain combinations can we have

Answer 31

300

Question 32

which process ensures only 1 heavy and 1 light chains are expressed

Answer 32

allelic exclusion

Question 33

RAG-1 and RAG-2 genes encode lymphoid-specific components of the recombinase

Answer 33

True