Ch. 5: Antibody Structure and Function

Question 1

What are antibodies

Answer 1

antibodies are immunoglobulins that play a key role in the humoral immune response

Question 2

Where is the highest concentration of antibodies found

Answer 2

in the serum

Question 3

What percentage of antibodies are glycoproteins

Answer 3

80-95%

Question 4

What percentage of antibodies are carbohydrates

Answer 4

1-15%

Question 5

What are the five major classes of antibodies

Answer 5

• IgG
• IgA
• IgM
• IgE
• IgD

(GAMED)

Question 6

What is the main function of antibodies

Answer 6

To bind foreign antigens and neutralize or eliminate foreign invaders

Question 7

What is the basic structure of an immunoglobulin

Answer 7

a four chain polypeptide structure

Question 8

What are the two types of peptide chains in an immunoglobulin

Answer 8

Heavy (H) and Light (L) chains

Question 9

How many heavy and light chains does an immunoglobulin have

Answer 9

two heavy and two light chains

Question 10

What holds the chains of an immunoglobulin together

Answer 10

Noncovalent forces and S=S disulfide bonds

Question 11

What is the function of the variable region (amino-terminal end) of an immunoglobulin

Answer 11

allows for specific binding to a particular antigen

Question 12

Where are the constant regions located in an immunoglobulin, and what is their function

Answer 12

The constant regions (carboxy-terminal end) are responsible for the biological functions of the antibody.

Question 13

How many constant regions do immunoglobulins have

Answer 13

3-4 constant regions

Question 14

How are heavy chains in immunoglobulins denoted

Answer 14

by greek letters specific to each Ig class

Question 15

What domains do heavy chains have

Answer 15

• one variable domain (VH)
• 3-4 constant domains (CH1, CH2, CH3, CH4)

Question 16

What are the two types of light chains in immunoglobulins?

Answer 16

Kappa (κ) and Lambda (λ)

Question 17

Can an immunoglobulin molecule have both types of light chains

Answer 17

No, a single immunoglobulin molecule has only one type of light chain

Question 18

What is the function of the hinge region in immunoglobulins

Answer 18

• Provides flexibility of Fab arms
• assists in initiation of complement cascade and Fc receptor binding

Question 19

What domains do light chains contain

Answer 19

• 2 variable light chain domains (VL)
• 2 constant light chain domains (CL)

Question 20

Where is the hinge region located

Answer 20

between the CH1 and CH2 regions of a Ig

Question 21

Where is the carbohydrate portion located

Answer 21

located between the CH2 domains

Question 22

What is the function of the carbohydrate portion of immunoglobulins

Answer 22

• Increases solubility
• provides protection against degradation of molecule
• enhances functional activity of the Fc domain

Question 23

What are the two major structural regions of an antibody?

Answer 23

• Fab region
• Fc region

Question 24

What does the Fab region do and what is it made of

Answer 24

• Antigen binding site
• consists of light chain and half of the heavy chain

Question 25

What does the Fc region do and what is it made of

Answer 25

* interacts with host systems, promotes clearance of antigens and activates immune responses * consists of half of the heavy chain

Question 26

What happens when an antibody is treated with papain

Answer 26

* Produces two Fab fragments (antigen-binding, no effector function) * Produces one Fc fragment (mediates effector function, cannot bind antigen

Question 27

What happens when an antibody is treated with pepsin?

Answer 27

* Produces Fab fragments (two antigen-binding sites held together) Produces Fc fragment (non-functional pieces)

Question 28

What are isotypes in immunoglobulins

Answer 28

Unique amino acid sequences common to all Igs of a given class or subclass, located in the constant region of heavy chains

Question 29

List the heavy chains associated with each Ig class

Answer 29

IgG: γ (gamma) IgM: μ (mu) IgA: α (alpha) IgD: δ (delta) IgE: ε (epsilon)

Question 30

What is the clinical significance of isotypes

Answer 30

Used for Ig quantitation, diagnosing immunodeficiency diseases, and classifying B cell leukemias

Question 31

What are allotypes in immunoglobulins

Answer 31

Minor variations in amino acid sequences found in some individuals of the same species, inherited and individual-specific

Question 32

Where are allotypes located

Answer 32

In the constant regions of the four IgG subclasses, one IgA subclass, and the λ light chain

Question 33

What is the clinical significance of allotypes

Answer 33

Used in bone marrow graft monitoring, forensics, and paternity testing

Question 34

What are idiotypes in immunoglobulins

Answer 34

Variations in the variable regions that give antibodies their specificity to a particular antigen

Question 35

Where are idiotypes located

Answer 35

In the variable heavy (VH) and variable light (VL) chain regions

Question 36

What is the clinical significance of idiotypes

Answer 36

Used in immune response regulation, vaccines, and B cell tumor treatments

Question 37

Which immunoglobulin is the predominant antibody in humans

Answer 37

IgG

Question 38

What percentage of total serum immunoglobulin does IgG constitute

Answer 38

70-75%

Question 39

Which immunoglobulin has the longest half-life, and how long is it

Answer 39

IgG, with a half life of 23 days

Question 40

What type of heavy chains does IgG have

Answer 40

Gamma (γ) heavy chains

Question 41

Does IgG production require T-cell help

Answer 41

yes

Question 42

How many subclasses of IgG exist, and what are they

Answer 42

* IgG1 * IgG2 * IgG3 * IgG4

Question 43

How do IgG subclasses differ from each other?

Answer 43

They have slight differences in constant region amino acid sequences, number, and position of disulfide bridges

Question 44

Which IgG subclasses respond to protein antigens?

Answer 44

IgG1 and IgG3

Question 45

Which IgG subclasses respond to polysaccharide antigens?

Answer 45

IgG2 and IgG4

Question 46

What are the major functions of IgG?

Answer 46

Complement activation, antigen opsonization, ADCC, toxin and virus neutralization, newborn immunity, and precipitation/agglutination (in vitro).

Question 47

Which IgG subclass is the most efficient at complement activation

Answer 47

IgG3, followed by IgG1

Question 48

What is antibody-dependent cell-mediated cytotoxicity (ADCC)?

Answer 48

A process where IgG binds to target cells, allowing NK cells and other immune cells to destroy them.

Question 49

Which immunoglobulin is the only one that can cross the placenta

Answer 49

IgG

Question 50

Why is IgG important for newborn immunity?

Answer 50

It provides passive immunity by crossing the placenta and protecting the infant after birth

Question 51

What Ig is the largest of all the classes

Answer 51

IgM (M for mega fatty)

Question 52

What is another name for IgM

Answer 52

macroglobulin

Question 53

What percentage of total serum immunoglobulins does IgM account for?

Answer 53

5-10%

Question 54

What is the half-life of IgM

Answer 54

6 days

Question 55

In what two forms can IgM exist?

Answer 55

* Membrane-bound monomer (on B cell surface) * Pentamer (in blood)

Question 56

What structure holds the pentameric form of IgM together

Answer 56

The J chain that forms disulfide bonds

Question 57

How many antigen-binding sites does IgM have in its pentameric form?

Answer 57

10 antigen-binding sites

Question 58

Describe the structural arrangement of IgM.

Answer 58

It has a star-like shape with Fc regions in the center and Fab arms extended outward