Lymphocyte Receptor Genetics Flashcards
The immune system must be capable of:
- generating diverse repertoire of receptors
- minimize the expression of receptors
What are the recognition receptors of pathogens?
- germline encoded: PRRs
- randomly generated: BCR, TCR
B-cells recombine which gene segments to create different possible antibodies? Select all that apply.
A. (V)
B. (D)
C. ( J )
D. (C)
V, D, J, C
On the BCR, where does the effector activity occur?
Heavy chains (Ig: M, G, A, D, E)
The light chain genes on BCRs are encoded by:
A. (V, J, C) gene segments
B. (V, D, J, C) gene segments
A. (V, J, C) gene segments
Which gene segments is the heavy chain encoded by on BCRs.
- V, D, J, C
Does the progenitor or mature B-cell have DNA that was taken out and randomly combined?
- mature Bcells
Is this a light or heavy chain in a mature B-cell?
- light chain
Is this a light or heavy chain in a mature B-cell?
- heavy chain
How is the enormous diversity of the antibody repertoire solved?
- ability of developing B-cells to recombine the V, D, J gene segments
List the 5 mechanisms of VDJ recombination.
- RAG1/2
- TdT: terminal deoxyribonucleotidyl transferase
- Artemis
- DNA ligase
- ATM
How are the different V, D, J, C gene sequences selected for recombination?
- recombination is directed by signal sequences called RSSs
What is composed in each RSSs?
- heptamer - 23bp nucleotide - nonamer
- heptamer - 12bp nucleotide - nonamer
Do the RSSs bring together the spacers or separate them?
brings together appropriate gene segments during the generation of light/heavy chain variable region genes
What are RAG1/2 and their function?
RAG1/2 (recombination activation gene) : recognizes RSS and cuts the DNA at that region
What are the 3 steps of RAG1/2? What is the product?
Step 1: RAG1/2 binds to RSSs
Step 2: cleaves the DNA at the 5’ boarder of the heptamer
Step 3: hydroxyl group binds to the phosphate at the 3’ coding end,
Products: a sealed hairpin coding end and left over signal end
What is Artemis and its function?
Artemis: enzyme, endonuclease
Function: cleaves hairpin formation at coding joint
What kind of openings of the hairpin can Artemis create?
- 3’ or 5’ overhang
- blunt end
What does the cleavage of the hairpin by Artemis generate?
- sites for P nucleotides (palindrome) binding
What is ATM and its function?
ATM: kinase
Function: repairs double-stranded DNA breaks
What is DNA ligase and its function?
DNA ligase: ligase
Function: binds the cut ends of DNA
The effects of Artemis can result in the loss of nucleotides on either or both sides of the coding joint. What fixes this?
A. ATM
B. DNA ligase
C. TdT
D. RAG1/2
C. TdT
What is the function of TdT?
- adds nontemplated nucleotides following hairpin cleavage
List the 3 steps of the VDJ recombination mechanism.
- RAG1/2 proteins bind to RSSs and cleaves DNA
- forms hairpin loop - TdT adds contemplated nucleotides (N nucleotides)
- ATM and DNA ligase repair coding joints
Can V(D)J recombination occur between segments transcribed in either the same or opposite directions?
Both, as long as RSSs are lined up
What are the mechanisms that generate antibody diversity in B-cells?
- Multiple gene segments (VDJ)
- Heavy/Light chain combinatorial diversity
- P nucleotide addition between joints
- Nontemplated nucleotide (N) addition mediated by TdT activity
Mature B cells express which antibodies?
IgM and IgD
What determines whether the BCR is an IgM or IgD?
mRNA splicing
What does mRNA splicing control on B-cell receptor expression?
- producing membrane-bound or secreted IgM antibody
The TCR proteins consist of what subunits and gene segments?
(α) subunit: V, J segment
(β) subunit: VJD
T/F. The light chain of TCRs has more than one constant region and has VDJ segments.
False. The heavy chain of BCRs has more than one constant region and has VDJ segments.
Which of the following gene segments is NOT found in the IgL loci?
a. V
b. J
c. D
d. C
e. All the answers are found in the IgL loci
c. D
At which point in the variable segments does the RAG1/2 complex introduce a single-strand break into the
DNA during somatic recombination?
a. Between the coding region and the conserved heptamer
b. Between the conserved heptamer and the 12-bp spacer
c. Between the 23-bp space and the conserved nonamer
d. Between the nonamer and the 12-bp spacer
e. None of the answers are correct
a. Between the coding region and the conserved heptamer
- Several proteins must work in a coordinating fashion to achieve V(D)J recombination. Which one is
responsible for adding non-templated nucleotides to the V-D and D-J joints of Ig heavy chains?
a. Artemis
b. RAG1/2
c. DNA ligase
d. TdT
e. ATM
d. TdT
- Recognition spacer sequences (RSSs) are separated by how many base pairs?
a. 12
b. 23
c. 7
d. 9
e. 7 or 9
f. 12 or 23
f. 12 or 23
- Which of the following protein-encoding genes, although present in genomic DNA, are uniquely expressed
by lymphocytes?
a. RAG1/2
b. DNA ligase
c. TdT
d. ATM
e. Artemis
f. RAG1/2 and TdT
f. RAG1/2 and TdT
