Antibody Fine Structure

Question 1

What does mercaptoethanol do? And why?

Answer 1

Breaks -S-S- bonds

To produce equal amounts of HEAVY and LIGHT chains

Question 2

Weight of the light (L) chains?

Answer 2

~25kDa

Question 3

Weight of the heavy chains?

Answer 3

~50kDa

Question 4

How are the heavy and light chains bound?

Answer 4

By disulphide bridge

Question 5

Does a disulphide bridge link the H chains or L chains?

Answer 5

H chains

Question 6

Each H and L contains an amino-terminal variable (V) region. How many amino acids does it contain? And what do they differ in?

Answer 6

100-110 that differ from one antibody to the next

Question 7

What is the remainder of each chain called?

Answer 7

Constant (C) region

Question 8

Where are the amino and carboxyl ends of the antibody?

Answer 8

NH3+ at top

COO- at base

Question 9

What are parts of the variable region called? And what are they?

Answer 9

Hypervariable or complimentarity-determining regions (CDRs)

3 on both H & L constitute the antigen binding site

Question 10

What attaches to the C region?

Answer 10

Carbohydrates

Question 11

What do some H chains contain?

Answer 11

(γ, δ, α) proline-rich hinge

Question 12

What size of loops are formed by the folding of H & L?

Answer 12

60aa

Question 13

How are effector functions mediated?

Answer 13

Constant domains

Question 14

What are the classes of antibody?

Answer 14

IgG, IgE, IgD, IgA, IgM

Question 15

How are the classes of Ig determined?

Answer 15

Kind of H chain

(γ, α, ε, δ, μ) = isotypes

Question 16

What are the kinds of L chain?

Answer 16

κ and λ

Only 1 type for each Ab molecule, not both

Question 17

Which classes are monomers? Dimers? And pentamers?

Answer 17

IgG, IgE, IgD are monomers
IgA is a dimer
IgM is a pentamer

Question 18

What are IgA and IgM joined by?

Answer 18

J chain

Question 19

What are the subclasses of IgA and IgG

Answer 19

IgA1 and IgA2 due to minor differences in H chain

IgG1-5

Question 20

Ig fine structure is determined by organisation of the protein. What are the 1°, 2°, 3° & 4° structures?

Answer 20

1- aa sequence (V & C of H & L)
2- antiparallel β- pleated sheets
3- compact globular domains
4- interactive functional domains

Question 21

What are conformational changes in antibody induced by?

Answer 21

Antigen binding

Question 22

How are epitopes caught?

Answer 22

Loops (H1-3 & L1-3) in binding pocket MOVE to surround and capture the epitope

Question 23

Is the movement of antibody arms dependent or independant?

Answer 23

Independant

Question 24

Which Ig crosses the placenta?

Answer 24

IgG

Question 25

Which Ig induces mast cell degranulation?

Answer 25

IgE

Question 26

Which Ig is first to be produced in primary Ab response?

Answer 26

IgM - good agglutinator as pentamer

Question 27

Which Ig has a secretory component?

Answer 27

IgA is protease resistant

Question 28

Since Ig are glycoproteins, they can function as potent i——–

Answer 28

Immunogens

Question 29

What does isotype describe?

Answer 29

(C region) describes Ig class and subclass is all members of the same species (eg IgG1 or IgM)

Question 30

Allotypic determinants are?

Answer 30

Multiple alleles for some genes in H or L chain (between strains/ families within a species)

Question 31

Idiotypic determinants are?

Answer 31

Idiotope= epitope in variable region, within or outside antigen binding site, different for each individual

Question 32

What are immunoglobulins able to do?

Answer 32

Respond to a limitless array of antigens = 10^10 different antibodies each with its own specificity

Question 33

How is C region maintained alongwith diverse V region?

Answer 33

2 theories

Germ-line theory (large repertoire of Ig genes in germ cells = eggs and sperm)
Somatic-variation theory (small number genes mutate/ recombine in somatic cell)

Question 34

What is the diversity of antibodies due to?

Answer 34

Genomic rearrangement - shown only by lymphocytes

Question 35

What happens as a B cell matures?

Answer 35

Gene segments are RANDOMLY SHUFFLED

this process is carefully regulated

Question 36

After B cell matures, it contains chromosomal DNA that is no longer identical to what?

Answer 36

Grem-line DNA

Question 37

What do V, J, D and C stand for (gene segments)

Answer 37

V Variable
D diverse
J joining
C constant

Question 38

B cells exhibit ‘Allelic Exclusion’. What is it?

Answer 38

B cells contain both maternal and paternal chromosomes, but EXPRESS ONLY ONE for H and L chains

Question 39

Somatic Hypermutation:
• Once a functional v………-r………. gene unit is formed it can be a……..! Occurs in g……….. c……….. during formation of memory B cells
•P………. s………. occurs once a……… interacts with membrane Ig, for those mutations that have increased a……….. of a………. (Affinity Maturation)

Answer 39

• Once a functional VARIABLE-REGION gene unit is formed it can be ALTERED! occurs in GERMINAL CENTRES during formation of memory B cells
• POSITIVE SELECTION occurs once ANTIGEN interacts with membrane Ig, for those mutations that have increased AFFINITY of ANTIBODY (Affinity Maturation)

Question 40

What is Class/Isotype Switching? And what is it controlled by?

Answer 40

B cells can SWITCH Ig class, without loss of specificity

Controlled by T helper cell cytokines IL-4 and IL-10