Antibodies genetics and structure

Question 1

What is the Ab molecule made of?

Answer 1

Glycoprotein

2 heavy chains (V+C), 2 light (V+C)

Question 2

What are hypervariable regions?

Answer 2

3 regions on H and 3 regions on L. CDR1,2,3

AA on CDR complements AA on Ag

Question 3

How many different heavy chains are there? (names)

How many different light chains?

Answer 3

9 different heavy : IgG1-4, IgA 1-2, IgD, IgE, IgM

2 dif light: kappa or lamda

Question 4

How does variability of constant region come about?

Answer 4

When Ig genes recombine

Question 5

Genes on human heavy chain locus are:

How are they organised

Answer 5

38-46 VH genes, 27 DH genes, 6 JH genes

Organised in clusters upstream of constant regions

Question 6

Genes on human lamda locus

Answer 6

30 V lamda genes, five J lamda, each J lamda followed by constant segment

Question 7

Genes on human kappa locus:

Answer 7

34-40 Vkappa genes and 5 J kappa genes, J upstream of constant

Question 8

Describe genetic recomb:

Answer 8

When HPSC differentiates to B cell - start to recombine Ig gene
1- pick 1/27 D and put it next to J, cut loop
2- pick 1/40 V and put it next to DJ, cut loop
3- Then still everything between VDJ and C is still there - when transcripted to mRNA, splice out bits in between

Question 9

CDR 1, 2, 3 bits:

Answer 9

CDR 1 and 2 - only V

CDR 3 - VDJ

Question 10

How do you recombine LC?

Answer 10

Same way, start kappa, if not successful, do lamda

Question 11

Chances at Ig Building

Answer 11

1 set of genes from mom, one set from dad. So 2 chances at HC, and 4 at LC

Question 12

How much variability due to genetic recombination?

Answer 12

1.3x10^6 + additional

Question 13

What is VDJ recomb mediated by?

Answer 13

Recombinase enzyme coded by RAG 1 and 2 recognising RSS on nucleotides flanking VDJ.

Question 14

Structure and Types of RSS, why?

Answer 14

Both heptomer space nanomer
Heptomer and nanomer sequence and length conserved
Space length conserved either 12 or 23
12 can only recombine with 23 - so 1 V, 1 D, 1 J

Question 15

4 ways to get additional diversity:

Answer 15

• exact location of splice isn’t set so inaccuracies
• N-nucleotide addition by TDT before religation
• Chain combinations
• Somatic hypermutation (point mutations)

Question 16

Upto how many different antibodies can we get?

Answer 16

10^15

Question 17

How and when do you class switch?

Answer 17

So first, heavy chain recombines VDJ, then makes IgM
then class switch
eg c mue to c epsilon looped out

Question 18

Are RSS used in class switching?

Answer 18

No, switch sequence is upstream of enzyme for each C, and different enzyme is used too

Question 19

Why does Naive B cell make both IgM and IgD?

Answer 19

Only one switch seq before mue, non before delta

Question 20

How are antibodies flexible?

Answer 20

Have hinge regions at their neck

Question 21

Can antibodies make polymers? explain:

Answer 21

Secretory IgA is a dimer, circ monomer

Circ IgM is pentamer, cell surface monomer