Lymphocyte Receptor Genetics

Question 1

The immune system must be capable of:

Answer 1

• generating diverse repertoire of receptors
• minimize the expression of receptors

Question 2

What are the recognition receptors of pathogens?

Answer 2

• germline encoded: PRRs
• randomly generated: BCR, TCR

Question 3

B-cells recombine which gene segments to create different possible antibodies? Select all that apply.
A. (V)
B. (D)
C. ( J )
D. (C)

Answer 3

V, D, J, C

Question 4

On the BCR, where does the effector activity occur?

Answer 4

Heavy chains (Ig: M, G, A, D, E)

Question 5

The light chain genes on BCRs are encoded by:
A. (V, J, C) gene segments
B. (V, D, J, C) gene segments

Answer 5

A. (V, J, C) gene segments

Question 6

Which gene segments is the heavy chain encoded by on BCRs.

Answer 6

• V, D, J, C

Question 7

Does the progenitor or mature B-cell have DNA that was taken out and randomly combined?

Answer 7

• mature Bcells

Question 8

Is this a light or heavy chain in a mature B-cell?

Answer 8

• light chain

Question 9

Is this a light or heavy chain in a mature B-cell?

Answer 9

• heavy chain

Question 10

How is the enormous diversity of the antibody repertoire solved?

Answer 10

• ability of developing B-cells to recombine the V, D, J gene segments

Question 11

List the 5 mechanisms of VDJ recombination.

Answer 11

1. RAG1/2
2. TdT: terminal deoxyribonucleotidyl transferase
3. Artemis
4. DNA ligase
5. ATM

Question 12

How are the different V, D, J, C gene sequences selected for recombination?

Answer 12

• recombination is directed by signal sequences called RSSs

Question 13

What is composed in each RSSs?

Answer 13

1. heptamer - 23bp nucleotide - nonamer
2. heptamer - 12bp nucleotide - nonamer

Question 14

Do the RSSs bring together the spacers or separate them?

Answer 14

brings together appropriate gene segments during the generation of light/heavy chain variable region genes

Question 15

What are RAG1/2 and their function?

Answer 15

RAG1/2 (recombination activation gene) : recognizes RSS and cuts the DNA at that region

Question 16

What are the 3 steps of RAG1/2? What is the product?

Answer 16

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

Question 17

What is Artemis and its function?

Answer 17

Artemis: enzyme, endonuclease
Function: cleaves hairpin formation at coding joint

Question 18

What kind of openings of the hairpin can Artemis create?

Answer 18

1. 3’ or 5’ overhang
2. blunt end

Question 19

What does the cleavage of the hairpin by Artemis generate?

Answer 19

• sites for P nucleotides (palindrome) binding

Question 20

What is ATM and its function?

Answer 20

ATM: kinase
Function: repairs double-stranded DNA breaks

Question 21

What is DNA ligase and its function?

Answer 21

DNA ligase: ligase
Function: binds the cut ends of DNA

Question 22

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

Answer 22

C. TdT

Question 23

What is the function of TdT?

Answer 23

• adds nontemplated nucleotides following hairpin cleavage

Question 24

List the 3 steps of the VDJ recombination mechanism.

Answer 24

1. RAG1/2 proteins bind to RSSs and cleaves DNA
   - forms hairpin loop
2. TdT adds contemplated nucleotides (N nucleotides)
3. ATM and DNA ligase repair coding joints

Question 25

Can V(D)J recombination occur between segments transcribed in either the same or opposite directions?

Answer 25

Both, as long as RSSs are lined up

Question 26

What are the mechanisms that generate antibody diversity in B-cells?

Answer 26

1. Multiple gene segments (VDJ) 2. Heavy/Light chain combinatorial diversity 3. P nucleotide addition between joints 4. Nontemplated nucleotide (N) addition mediated by TdT activity

Question 27

Mature B cells express which antibodies?

Answer 27

IgM and IgD

Question 28

What determines whether the BCR is an IgM or IgD?

Answer 28

mRNA splicing

Question 29

What does mRNA splicing control on B-cell receptor expression?

Answer 29

- producing membrane-bound or secreted IgM antibody

Question 30

The TCR proteins consist of what subunits and gene segments?

Answer 30

(α) subunit: V, J segment (β) subunit: VJD

Question 31

T/F. The light chain of TCRs has more than one constant region and has VDJ segments.

Answer 31

False. The heavy chain of BCRs has more than one constant region and has VDJ segments.

Question 32

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

Answer 32

c. D

Question 33

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

Answer 33

a. Between the coding region and the conserved heptamer

Question 34

3. 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

Answer 34

d. TdT

Question 35

4. 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

Answer 35

f. 12 or 23

Question 36

5. 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

Answer 36

f. RAG1/2 and TdT