Lecture 7 Flashcards
(16 cards)
what is gene rearrangement?
the process that produces specifc antigen receptors due to rearrangement of antibody variable regions
a VJ chain indicates what?
a light chain
a VDJ chain indicates what?
a heavy chain
what are the steps of recombination? (4)
- somatic recombination
- transcription
- splicing
- translation
in what order to the segments of antibody loci join during recombination?
(you start with —-V—-(D)—-J—-C—-)
- (if heavy chain, J joins D)
- (D)J joins V
- C joins V(D)J
What are components of the recombination signal sequences (RSSs)
(the 12/23 rule things)
- heptamer - 23 bp - nonamer -
OR
- nonamer - 12bp - heptamer -
What is the 12/23 rule?
segments must always join in a 12-23 fashion. It can never be 12-12 or 23-23.
What are the 3 loci that encode IG chains (i.e. b cells)
How are they different?
- λ light chain locus (w J regions seperated)
- κ light chain locus (w J regions together)
- heavy chain locus (w D segment)
What are the 2 loci that encode TCR chains (i.e. t cells)
How are they different?
- α-chain locus (w no D segment)
- β-chain locus (w D segment)
what are the enzymatic steps in V(D)J Recombination?
- recombination singals (RSSs) are brought together by a looping event.
- RSSs bind to V(D)J recombinase, which is made up of RAG-1 and RAG-2.
- V(D)J recombinase makes double-stranded breaks at the RSS-coding junctions
- broken ends are brought together by nonhomologous end joining (NHEJ) enzymes – Ku70 and Ku80 bind to the ends and recruit the DNA repair enzyme, DNA-PK.
- Ku70 and Ku80 phosphorylate/activate Artemis
- Artemis opens the hairpins from the double stranded breaks of coding joints.
- Terminal Deoxynucleotidyl Transferase (TdT) adds nucleotides to the broken DNA ends of coding joints.
- DNA ligase IV and XRCC4 mediate the ligation of the processed broken ends.
what are the products of V(D)J Recombination? What happens to them?
- imprecise coding joint: kept o generate diversity
- precise coding joint: extra stuff we dont need, gets lot on the genome.
what is combinational diversity?
diversity due to different V(D)J segments
what is junctional diversity?
diversity due to different N and P nucleotides in each segment
what are the steps of junctional diversity production?
- RSSs are brought together
- RAG complex cleaves DNA at random sites, producing single-stranded DNA ends.
- Artemis and DNA-PK open up DNA hairpins to generate palandromic P-nucleotides
- N-nucleotides are added by TdT
- strands are paired
- gaps are filled in by DNA synthesis and ligation
What kind of antibody is produced by an mRNA transcript with a preserved AAA sequence?
a transmembrane Ig
What kind of antibody is produced by an mRNA transcript with a non-preserved AAA sequence?
a secreted Ig
