BIOL 435 Ch. 6 Part One (Organization+Expression of Lymphocyte Receptor Genes)

Question 1

papain digestion (Ab structure)

Answer 1

• 1 Fc

- 2 seperate Fab

Question 2

pepsin digestion (Ab structure)

Answer 2

• 1 pFc (got ‘rid of it’)

- 1 F(ab)2

Question 3

different BCRs generated

Answer 3

-1x10^13 possibilities

>10 to 100 trillion

Question 4

mechanisms used by B-cells to produce repertoire

Answer 4

• by very elegant experiments in 1970s

- Susumu Tonegawa: nobel prize

Question 5

the same CH or CL

Answer 5

-can be connected to millions of different VH or VL regions

Question 6

same VH region

Answer 6

-can be connected to different CH regions (5 Ig types)

Question 7

2-germ line theories

Answer 7

1. Dreyer and Bennett proposed 2 genes might be required to encode H and L chains
2. Somatic Hypermutation theory

Question 8

somatic hypermutation theory

Answer 8

• mutational process only in B-cells

- enhances the antigenic repertoire after Ag stimulation

Question 9

puzzle of IG gene structure

Answer 9

-variable (V)
-diversity (D)
>used in Ab heavy chains only
-joining (J)
-constant (C): ex. IgM

Question 10

light chains

Answer 10

• kappa
• lambda
• mice almost always have kappa
• humans 40% lambda

Question 11

chromosomes for chains

Answer 11

• different places for light and heavy types
• 4 places for light chain (2 mom+dad, Kappa+beta)
• 2 places for heavy (mom+dad)

Question 12

how do we get variability in BCRs and TCRs?

Answer 12

1. Inherit V, D and J segments
2. Recombine gene segments
3. Recombinational inaccuracy
4. Random assortment of chains
5. Somatic Hypermutation (B-cells only)
6. Exonuclease trim

Question 13

inherit multiple V, D and J segments

Answer 13

-make up variable portion of heavy chain (B-cells) or beta-chain (T-cells)

Question 14

recombinational inaccuracy

Answer 14

-enzymes add AA ‘randomly’ even though exact same segments were used

Question 15

order of chains

Answer 15

• heavy or beta-chain made first

- if get a functional one, then light or alpha-chain is made

Question 16

B-cell (chain production)

Answer 16

-in bone marrow
-recombines heavy chain
-makes VpreB (‘surrogate light’)
>fully light chain not made yet
-if passes ‘pre-test’, cell proliferates (all same VH)
>could get different light chains

Question 17

T-cell (chain production)

Answer 17

-in thymus
-recombines beta-chain
-makes preTalpha
-pre-test (cell-surface)
>postive, negative selection

Question 18

Tonegawa’s classic experiments

Answer 18

• showed that 2 DNA segments (V and C kappa) are brought together by recombination only in B lymphocytes
• each B-cell contains a single functional combination
• different gene segments are used in each B-cell

Question 19

heavy chain C region

Answer 19

• mu always closest, then delta

- both IgM and IgD on cell-surface before B-cell is activated

Question 20

light-chain arrangements

Answer 20

• arranged differently
• lambda: alternating V, C, J
• kappa: variables clustered together

Question 21

kappa light-chain genes

Answer 21

-include V, J and C segments

Question 22

mice V kappa gene families

Answer 22

• 18

- coding segments are separated by non-coding gaps of 5-100Kb

Question 23

downstream of V kappa genes

Answer 23

-four functional J kappa segments

Question 24

humans vs. mice

Answer 24

• humans have similar arrangement but with differing numbers of V kappa and J kappa genes
• mice: only 5% Igs have Lambda light chains
• humans: 40% of light chains are lambda

Question 25

heavy-chain gene organization

Answer 25

-includes 3 variable segments (V heavy, D heavy, and J heavy), combined with one C heavy segment

Question 26

humans express V heavy segments

Answer 26

• at least 45 functional V heavy segments

- mice express over 100 V heavy segments

Question 27

downstream of V heavy

Answer 27

-D heavy segments
>14 in mice
>23 in humans

Question 28

J heavy segments number

Answer 28

• 4 in mice

- 6 in humans

Question 29

8 C heavy regions exist

Answer 29

-encoding for different isotopes of Ab