lecture 2

Question 1

what segments are the heavy chain and TCR beta encoded by?

Answer 1

V region encoded by the gene segments: V, D and J

Question 2

what is the light chain and TCR alpha encoded by?

Answer 2

V region encoded by the gene segments: V and J

Question 3

how and where are Ig genes found?

Answer 3

in the genome as families of gene segments

Question 4

what occurs during B cell development of light chain?

Answer 4

-DNA containing Ig gene segments is deliberately broken between a V and J segment
-gene segments are rearranged to form functional Ig genes (exon)
-are transcribed and translated to give a new variable region of the antibody

Question 5

what is this process called?

Answer 5

non-homologous end joining recombination

Question 6

what two loci contain L chain genes?

Answer 6

kappa and lambda

Question 7

what happens to encode the heavy chain?

Answer 7

-B cell randomly breaks between a D and J segment bringing them together
-DNA is rebroken again
-brings the joined piece of DNA next to the V region and transcript joins

Question 8

how is DNA changed into a protein?

Answer 8

-somatic recombination where D-J rearrange
-then V-J or V-DJ join the rearranged DNA
-transcription occurs of primary transcript RNA
-splicing to form mRNA
-translation to reach the final polypeptide chain

Question 9

what is the order Ig rearrangements occur in B cell development?

Answer 9

1. heart chain gene segments rearrange (D-J and then V-DJ)
2. light chain gene segments rearrange (kappa segments V-J first)
3. if kappa unsuccessful, lambda segments V-J rearrange

Question 10

where is the H chain locus found?

Answer 10

chromosome 14

Question 10

where is the kappa chain locus found?

Answer 10

chromosome 2

Question 11

where is the lambda chain locus found?

Answer 11

chromosome 22

Question 12

how is the heavy chain organised in the human genome?

Answer 12

-each individual B cell breaks DNA bringing together the D and J region
-then join together the DJ to a V region

Question 13

what are recombination signal sequences?

Answer 13

-special sequences that flank each of the V, D and J gene segments
-bits of DNA that are recognised to bring the segments together

Question 14

what enzyme helps in rearrangement?

Answer 14

V(D)J recombinase which cut the DNA at the correct place to bring the segments together

Question 15

what does RAG genes stand for?

Answer 15

recombination activating gene

Question 16

what do RAG-1 and RAG-2 encode?

Answer 16

lymphoid specific components of the recombinase

Question 17

what do mutations in RAG genes lead to?

Answer 17

immunodeficiency

Question 18

what is allelic exclusion?

Answer 18

-each B cell has to make 1 antibody so is carried out on one chromosome
-process is now turned off so it doesn’t happen on the other chromosome as would produce more than one antibody for the cell

Question 19

what is light chain isotope exclusion?

Answer 19

each B cell expresses either a rearranged kappa OR lambda light chain - never both

Question 20

what are the mechanisms for generation off antibody diversity?

Answer 20

1. multiple gene segments for each chain
2. combinatorial diversity - different V, D and J segments recombine to produce different sequences
3. combinations of heavy and light chains
4. junctional diversity increases diversity of variable region
5. somatic hypermutation

Question 21

what are the additions in junctional diversity?

Answer 21

-imprecise joining (small differences in sequence where VD and DJ segments join)
-N regions - random addition of nucleotides at junctions od VD and DJ by terminal transferase

Question 22

what is somatic hypermutation?

Answer 22

-mutation frequency in antibody is orders of magnitude higher than seen in other areas of genome

Question 23

where does somatic hypermutation occur?

Answer 23

in germinal centres
-as B cells recognise antigen and proliferate/become activated

Question 24

how does somatic hypermutation (SHM) occur?

Answer 24

-AID acts on DNA to de-aminate cytosine to uracil
-uracil is then recognised by error prone DNA repair pathways leading to more mutations

Question 25

what is the constant region of each heavy chain encoded by?

Answer 25

C region gene segment

Question 26

what is thebfirst antibody to be expressed by each developing B cell?

Answer 26

IgM as Cu segment is physically closest to the V, D and J gene segments

Question 27

what does switching to other classes require?

Answer 27

-further DNA recombination
-guided by switch regions

Question 27

how does looping out to switch isotope occur?

Answer 27

-loops out the exon and joins the VDJ with new downstream constant region
-cuts the region out rearrange so cant be the same again