Lecture 7 - Creation of Antibody Diveristy

Question 1

Basic structure of a gene
1)
2)
3)
4)
5)

Answer 1

1) Promoter
2) Leader exon
3) Exons/introns
4) Enhancer
5) Poly A tail addition sequence

Question 2

Function of leader exon

Answer 2

Present on extracellular proteins
Encodes leader peptide
Leader peptide directs peptide towards ER for exocytosis

Question 3

Difference in shape between lambda and kappa light chain loci

Answer 3

Lambda has sequence of (J-C)n

Kappa has sequence of (J)n (C)n

Question 4

What is ‘germline configuration’?

Answer 4

Unrearranged minigenes at immunoglobulin locus.

How Ig locus is found in cells in body except for T and B lymphocytes

Question 5

What is a rosette?

Answer 5

Ig locus forms flower-like structures.

Minigenes near one another will join.

Question 6

How much of a light-chain variable-region protein is encoded by V genes?

Answer 6

~90%

Question 7

What do heptamers and nonamers do?

Answer 7

Join together to form loops which are removed by V(D)J recombinase complex

Question 8

How do heptamers and nonamers join?

Answer 8

Heptamers pair and nonamers pair.

They are complementary base sequences

Question 9

In a light chain, is the 23-nucleotide loop closer to the V or J region?

Answer 9

V region

Question 10

Which minigene region is flanked by 12-nucleotide spacers?

Answer 10

D region

Question 11

Which minigene region is next to the 23-nucleotide spacer?

Answer 11

V and J regions

Question 12

Order of minigene regions and spacers

Answer 12

—V—23 spacer—12 spacer—D—12 spacer—23 spacer—J—

Question 13

Function of 12/23 rule

Answer 13

Prevents V-J recombination in heavy chain

Question 14

If a minigene lies between V(D)J cassette and C region, what happens to it?

Answer 14

It is spliced out when mRNA of Ig gene is transcribed.

Splice sites are after V(D)J cassette and C region

Question 15

What do 12 and 23 bases correspond to?

Answer 15

Length of major and minor grooves of DNA

Question 16

Does the genome change length much with exonuclease and TdT activity?

Answer 16

Not much

Exonuclease and TdT activity are roughly in equilibrium

Question 17

Why can D region be absent in some antibodies?

Answer 17

Exonuclease function is inexact.

Can sometimes accidentally excise D region (which is small)

Question 18

Problems with TdT

Answer 18

Can add stop codons, frameshift in N regions

Question 19

What are N-regions?

Answer 19

Regions between V, D and J regions.
High diversity because of exonuclease and TdT activity.
Imprecision of V(D)J junctions

Question 20

Sources of antibody diversity
1)
2)
3)

Answer 20

1) Combinatorial diversity
2) Junctional diversity
3) Somatic hypermutation

Question 21

Can IgD and IgM be expressed by the same B cell?

Answer 21

Yes

IgM and IgD share a switch region (mu switch region)

Question 22

Can a change in framework region structure of antibodies change binding affinity?

Answer 22

Yes.

CDR loops can be moved into a more favourable or unfavourable position