L8 -VDJ recombination

Question 1

what number chromosone is the heavy-chain locus

Answer 1

14

Question 2

2 light chains

Answer 2

lambda - 22

kappa - 2

Question 3

VDJ recombination simple:

Answer 3

1. combinations of V + D + J regions
2. any combination of light chain with any combination of a lambda or kappa chain

Question 4

what is key about Rag-1 and 2 endonulceases

Answer 4

lymphocyte specific

= dont want ds breaks in normal cells

Question 5

RSS sequnces structure

Answer 5

contains 3 components :
heptamer - 12/23 spacer - nonamer

a 12 nucleotide spacer can only bind to a 23

Question 6

Rag-1 and Rag 2 mcehasim for cleavage at RSS

Answer 6

1. Rag uses water as nucleophile to attack 3’ hydroxyl

= nick formed

2. 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

Question 7

name of enzyme that undergoes junctional diversity/Non-homologous end joining in lymphocytes

Answer 7

TDT

= Terminal deoxynucleotidal transferase

Question 8

mechanism of junctional diversity

Answer 8

1. ku70/80 bind to hairpin loops
2. 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

3. TDT adds random nucleotides until complimentarity found

= new sequnce in between RSS sequnces

Question 9

which loop is mainly impacted by junctional diversity

Answer 9

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

Question 10

where does somatic hypermutation take place

Answer 10

germinal centres of lymph node
- light zone of germinal centre = somatic

• dark zone
  = affinity maturation with help of T follicular cells

Question 11

somatic maturation and class switching key enzyme

Answer 11

AID

= Activation Induced Deaminase

Question 12

how does somatic hypermutaion happen - AID + UNG

Answer 12

1. AID causes deamination of cytosines
   = uracil bases made
2. Normally would be repaired but overhwmling amount of AID

= acted on by UNG - Uracil-DNA glycolyase