Antibody Structure

Question 1

H chain

Answer 1

heavy chain, MW=50,000, each antibody has 2 H chains, each H chain has 1 variable domain (VH) and 3-4 constant domains (CH1, CH2, CH3, (CH4)), 5 kinds of H chains (gamma, alpha, mu, epsilon, delta—each corresponds to the appropriately named antibody: IgA has alpha chains

Question 2

L chain

Answer 2

light chain, MW= 25,000, each antibody has 2 L chains, each L chain has 1 variable domain (VL) and 1 constant domain (CL)

Question 3

kappa and lambda chains

Answer 3

2 varieties of L chain, each cell that makes antibody has a choice, but it uses only one kind.

Question 4

hinge region

Answer 4

allows for flexibility so that when bound to antigen, the constant part of the antibody can change conformation

Question 5

Fab

Answer 5

S–S bonds between the H chains fully reduced

Question 6

F(ab2)

Answer 6

2 Fabs still joined by S—S bond

Question 7

Fc

Answer 7

non-antigen binding region of the antibody, makes antibody participate in complement

Question 8

complementarity-determining regions (hypervariable regions)

Answer 8

light chain and heavy chain variable region is NOT uniformly variable, most of the variability is in 3 regions called hyper-variable regions of CDR’s, amino acids in this region comprise the actual antigen-binding site

Question 9

variable (V) and constant (C) domains,

Answer 9

• variable (V) domain: at N-terminal of antibody, differences in amino acid sequences between antibodies of different specificities
• constant (C) domains: region that is essentially identical on the antibodies, made up of 1 (in L chains and 4 (in epsilon and mu) compact, structurally similar domains called C domains.

Question 10

VL and CL

Answer 10

variable domain of light chain and constant domain of light chain

Question 11

VH and CH

Answer 11

variable domain of heavy chain and constant domain of heavy chain

Question 12

Diagram an electrophoretic separation of human, label the anode and cathode, and identify the albumin, alpha 1, alpha 2, beta and gamma peaks.

Answer 12

diagram this

Question 13

Name the 5 antibody classes, and their characteristic heavy chains.

Answer 13

a. IgG: 2 light and 2 gamma (heavy) chains
b. IgE: 2 light and 2 epsilon (heavy) chains
c. IgD: 2 light and 2 delta (heavy) chains
d. IgA: 4 light, 4 alpha (heavy) chains, 1 Joining chain and 1 Secretory component
e. IgM: 10 light, 10 mu and 1 joining chain

Question 14

Draw a diagram of the structure of typical molecules of each class, and label the heavy and light chains; Fc and Fab parts; J chains if any; antibody combining sites; main interchain disulfide bonds; and secretory component

Answer 14

Draw this

Question 15

Distinguish the 5 immunoglobin classes in terms of size, and for IgG, IgM and IgA, their approximate concentration of serum.

Answer 15

G: 150,000, serum = 1000 mg/dL
E: 190,000
D: 180,000
A: 400,000, serum = 200 mg/dL 
M: 900,000, 100 mg/dL

Question 16

Describe the structure of antibody combining sites.

Answer 16

Combining site is where the antibody binds to the antigen, is made up of V domains of both the H and L chain (VH and VL)

Question 17

Explain why complementarity-determining regions are also called hypervariable regions.

Answer 17

There are 3 hyper variable regions on the variable domain of light and heavy chains. These regions have amino acid variability. It is more functionally significant to call them complementarity-determining

Question 18

Give an example of an allotype

Answer 18

minor allelic differences in the sequence of immunoglobulins between individuals, determined by allotypes of your parents, useful in determining relatedness

Question 19

Give an example of a subclass

Answer 19

immunoglobulins are divided into subclasses because of slight differences in the amino acid sequences of their H chain C regions. IgG1, IgG2, IgG3, IgG4. IgA1, IgA2. IgM1, IgM2. IgD and IgE.

Question 20

Give an example of an idiotype

Answer 20

unique combining region, made up of the CDR amino acids of its L and H chain, that each antibody has. Anti-idiotype: antibodies made that recognize the unique sequence of that combining site.