Antibody structure and repertoire generation 2 Flashcards
Where is the heavy chain locus?
Chromosome 14
Where is the kappa light chain locus?
chromosome 2
Where is the lambda light chain locus?
chromosome 22
What is required for a functional heavy chain gene?
A V region to recombine with a D region and a J region–> VDJ recombination
Which bit of the antibody does the VDJ bit code for?
CDR3
Which regions make up light chains?
V and J regions
How do diff B cells code for diff antibodies?
The gene rearrangement is random in every cell
Why is the order always V-D-J?
Because of recombination signal sequences
What recombination signal sequence do V regions have?
7 (heptomer), 23 spacer, 9 (nonomer)
3’ to 5’ (D region is on the 3’ side of the RSS)
What recombination signal sequence do D regions have?
7 (heptomer), 12 spacer, 9 (nonomer) (either side going out so 7 is closest on each side)
What recombination signal sequence do J regions have?
7 (heptomer), 23 spacer, 9 (nonomer)
3’ to 5’ (J region is on 5’ side of the RSS)
What must two recombination signal sequences be in order for them to recombine?
Different
What does the RAG complex do?
Bind to two recombination sequences at random (e.g. D5 and J6)
Directs the recombination
What does RAG stand for in RAG protein?
Recombination Activation Gene
What is shared between T cell and B cell recombination?
The RAG machinery
How does the RAG protein join two bits of DNA together?
It loops out the DNA in between
Why do B and T cells have a little bit less DNA than most somatic cells?
When recombination occurs the DNA in between the recombined bits is looped out and lost
What is junctional flexibility?
The joining process of two bits also introduces more diversity
How does the RAG protein cut DNA?
It cuts it in such a way that there is a hairpin loop at the end
How are strands cut by the RAG complex joined together?
They open up–> little bit from one strand flips to be alongside the other strand so there is an overhang
What is formed when a hairpin is opened up and flipped?
A palindromic sequence (p nucleotides)
What does TDT stand for?
Terminal deoxynucleotidyl transferase
What does TDT do?
AN enzyme that adds N nucleotides at random
What are N nucleotides?
Non-templated nucleotides
Why does the join have a lot of diversity?
The p nucleotides and n nucleotides make it v diverse
What is a possible issue of adding N nucleotides?
Could accidentally code for a stop codon
Could not add a multiple of 3–> frame shift
When is TDT expressed and not expressed?
It is only expressed when heavy chains are rearranging, not light chains
What happens if a transmembrane domain is included in an antibody?
It will be incorporated into the membrane as a b cell receptor instead of a secreted antibody
