Immunoglobulin genes

Question 1

what is the difference in genes for a cell thats non-lymphoid and cell thats destined to become a B Cell?

Answer 1

non-lymphoid cells will have genes that produce Ig’s very far apart. This is germ line configuration

cells becoming B cells will have Ig genes close together due to somatic recombination

Question 2

What are the DNA segments of light chain and DNA segments of Heavy chain. What segments form what parts of the antibody?

Answer 2

light chain

• variable –> V and J make the variable region
• joining —->
• constant –> makes constant region

heavy chain

• variable —> VDJ make variable
• diversity
• joining
• constant –> makes constant

Question 3

true or false, lambda and kappa light chain gene segments are located on different chromosomes

Answer 3

true –> kappa is expressed more

Question 4

what is the order of genes for the light chain?

Answer 4

Leader –> variable –> joining –> constant

Question 5

what is the main difference between kappa and lambda light chains?

Answer 5

lambda light chain has 4 constant genes. For each one, there is one J gene located upstream of it.

–J1–C1—J2—C2 –> always selected together

for Kappa light chain there is only one C region and therefore the J regions randomly select to attach to it.

–J123456——C1—–

Question 6

what is the organization of the heavy chain gene locus?

Answer 6

leader –> variable –> diversity —> joining –> constant

VDJC

Question 7

t or f, the heavy chain is found on a different chromosome as the kappa and lambda chromosomes.

Answer 7

true

Question 8

what is the first two constant genes on the heavy chain?

Answer 8

IgM comes first always!! IgD comes second most of the time.

Question 9

Does the first gene rearrangement occur in the H or L chain?

Answer 9

always the H chain

Question 10

how many gene rearrangements occur for heavy chain ?

Answer 10

two

Question 11

what are the gene rearrangements for the heavy chain?

Answer 11

1. DJ –> a Diversity segment RANDOMLY joins a particular joining segment. Everything in between is excised.
2. Then a variable segment randomly joins the DJ segment. Again everything in between is excised.

Question 12

what two enzymes are responsible for cleaving the DNA and causing recombination?

Answer 12

RAG-1 and RAG-2

Question 13

Once the two rearrangements have occurred, what steps occur until the final heavy chain product is made (4)

Answer 13

1. transcription of modified DNA
2. RNA processing
   - Poly A tail added to Constant side
   - splicing of excess mRNA
3. translation occurs
4. protein is processed and sent to cell surface

Question 14

what occurs to the leader segment of the heavy chain?

Answer 14

its translated but cleaved off in protein processing

Question 15

What are the 9 functional gene segments of the heavy chain constant region?

Answer 15

IgG -gamma 1-4
IgM
IGA - alpha 1 and 2
IgD
IgE

Question 16

true or false, diversity gene segments are in lower numbers for heavy and light chains.

Answer 16

false.

there is no D segment in light chains
in heavy chains there are quite a few D genes.

Question 17

After the heavy chain has been recombined, how does the light chain get recombined?

Answer 17

there is only one gene rearrangement in which V joins with J !!

V—J—C

VJ—-C

depending on Kappa or lambda for which J is combined with V

Question 18

t or f, same processing occurs for light chain as it does for heavy.

Answer 18

true

transcription
mRNA processing –> splicing, polyA tail
translation
protein modification

Question 19

What is the functional unit of the gene locus that allows for gene recombination (i.e. where do RAG-1 and 2 act)?

Answer 19

RSS –> recombination signal sequences.

Question 20

explain how RSS’s work.

Answer 20

RSS segments flank each gene (variable, diversity if heavy, joining, and constant)

they are heptamer – (12/24)–nonamer

12 = a single turn RSS
24  = a 2 turn RSS
# = nucleotides
only single turns can pair with 2 turns (NOT 1:1 or 2:2) 

RAG enzymes recognize these sequences and cause excisions

Question 21

what does a turn refer to in RSS?

Answer 21

the number of nucleotide in a turn of helix in DNA

Question 22

t or f, the heptamer and nonamer sequences of RSS are conserved but the 12/24 isnt.

Answer 22

true.

Question 23

what is the purpose of RSS’s?

Answer 23

prevent improper gene rearrangement.

Question 24

explain the RSS organization of a heavy chain? Why does this prevent improper gene rearrangement?

Answer 24

Vh > (24) ——– ———< (24)J

since variable and joining chains are both two turn RSS’s they cannot recombine. This forces D to combine J first (DJ) and after V then combines with DJ to get VDJ which then gets transcribed.

Question 25

true or false, VDJ and VJ rearrangements (i.e. heavy chain and light chain) occur continuously over a B cells life.

Answer 25

false, they occur once!! After this, the B cell only secretes that antibody that was recombined for. (for a given epitope)