L8 -VDJ recombination Flashcards
what number chromosone is the heavy-chain locus
14
2 light chains
lambda - 22
kappa - 2
VDJ recombination simple:
- combinations of V + D + J regions
- any combination of light chain with any combination of a lambda or kappa chain
what is key about Rag-1 and 2 endonulceases
lymphocyte specific
= dont want ds breaks in normal cells
RSS sequnces structure
contains 3 components :
heptamer - 12/23 spacer - nonamer
a 12 nucleotide spacer can only bind to a 23
Rag-1 and Rag 2 mcehasim for cleavage at RSS
- Rag uses water as nucleophile to attack 3’ hydroxyl
= nick formed
- 3’ hydroxyl used to attack the 5’ end on complimentary/other strand
= phopsphodiester bond formed between the 2 strands = hairpin loop
= DNA after hairpin loop is removed
name of enzyme that undergoes junctional diversity/Non-homologous end joining in lymphocytes
TDT
= Terminal deoxynucleotidal transferase
mechanism of junctional diversity
- ku70/80 bind to hairpin loops
- artemesis recruited cleaving hairpin loop leaving palindromic sequnces
= DNA that used to be hydrogen bonded in complimentary strand is released and is now in same strand
= sequnce of C-G,T-A now reads C,T,G,A
= 3’ overhang
- TDT adds random nucleotides until complimentarity found
= new sequnce in between RSS sequnces
which loop is mainly impacted by junctional diversity
CDR3
codes for V-D-J segments
= lots of RSS sequnces to be cleaved by RAG
= lots of random nucleotides added in junctional diversity to resolve hairpin loops
where does somatic hypermutation take place
germinal centres of lymph node
- light zone of germinal centre = somatic
- dark zone
= affinity maturation with help of T follicular cells
somatic maturation and class switching key enzyme
AID
= Activation Induced Deaminase
how does somatic hypermutaion happen - AID + UNG
- AID causes deamination of cytosines
= uracil bases made - Normally would be repaired but overhwmling amount of AID
= acted on by UNG - Uracil-DNA glycolyase