Antibody structure

Question 1

What is an antibody?

Answer 1

secreted form of the immunoglobulin produced by a B cell.

Question 2

What are immunoglobulins?

Answer 2

antigen-binding molecules of B cells

Question 3

Antibody molecules are identical to the ______ component of the B cell receptor

Answer 3

immunoglobulin

Question 4

What are antibodies produced by?

Answer 4

plasma cells

Question 5

T or F: each antibody produced by a single B cell has the exact same specificity for antigen

Answer 5

true

Question 6

What is the clonal hypothesis?

Answer 6

There is an enormous repertoire of B cells that are produced in bone marrow- each B cell displays many copies of the same BCR on its surface.
During infection, lymphocytes with receptors that recognize the pathogen are activated and proliferate.

Question 7

A stimulated B cell gives rise to ____.

Answer 7

antibody-secreting plasma cells

Question 8

What is the basic structure of antibody molecules?

Answer 8

two identical copies of a heavy chain

two identical copes of a light chain

Question 9

Describe the regions of an antibody.

Answer 9

Variable region- area that recognizes antigens

Constant region- very few differences

Question 10

What stabilizes immunoglobulin domains?

Answer 10

disulfide bonds

Question 11

What binds the light chains to the heavy chains?

Answer 11

disulfide bond

Question 12

What is the Fc receptor?

Answer 12

receptors found on different phagocytes that can recognize different antibody isotypes
Also where complement binds

Question 13

What are structural characteristics of the light-chain V domain?

Answer 13

Made of alternating beta sheets
Beta-barrel arrangement is stabilized by interchain disulfide bond.
Sequence of beta-chain is almost always the same

Question 14

Where does most variability of light chains exist?

Answer 14

loop regions (hypervariable regions)

Question 15

Structural characteristics of light-chain C domain?

Answer 15

Beta-sheets.
Interchain disulfide bond.
Sequence is constant, loops mostly constant

Question 16

How many hypervariable regions are there in light chains?

Answer 16

3 (1,2, and 3)

Question 17

What are hypervariable regions separated by?

Answer 17

framework regions (1-4)

Question 18

What do framework regions encode?

Answer 18

alternating beta sheets of light chain molecule

Question 19

What is an antigen?

Answer 19

any molecule that is bound by an antibody or a T cell receptor

Question 20

What is an epitope or antigenic determinant?

Answer 20

portion of an antigen that is bound by antibody molecule

Question 21

Antibody binding is _____ and _____.

Answer 21

non-covalent and reversible

Question 22

What is antibody binding mediated by?

Answer 22

electrostatic forces
hydrophobic interactions
van der waals forces
hydrogen-bonding

Question 23

What is affinity?

Answer 23

binding strength

Question 24

Antibodies have (few/many?) restrictions with respect to binding.

Answer 24

few

Question 25

What can antibodies bind to?

Answer 25

Native or denatured proteins, peptides Other types of molecules (carbs, nucleic acids, small molecules, chemicals) Soluble or particulate antigens.

Question 26

What do T cells (always) recognize?

Answer 26

peptides

Question 27

What is a linear epitope? discontinuous epitope?

Answer 27

linear- string of amino acids in a row | discontinuous- formed by tertiary structure of protein

Question 28

T cell receptors only recognize ____ epitopes

Answer 28

linear

Question 29

What is a multivalent antigen?

Answer 29

An antigen with many copies of an epitope or multiple epitopes

Question 30

What are the roles of antibodies?

Answer 30

membrane bound: specific antigen receptors for B cells | secreted: bridge btw acquired and innate immune system.

Question 31

What are functions of secreted antibodies?

Answer 31

mark microbes or infected cells for destruction by phagocytes (opsonization) or NK cells (antibody-dependent cell-mediated cytotoxicity) Activates complement pathway

Question 32

What is neutralization?

Answer 32

antibodies bind to pathogens and toxins and hinder them from interacting with host cells

Question 33

What is the most abundant isotype?

Answer 33

IgG

Question 34

What is the major difference between the subtypes of IgG?

Answer 34

the hinge region

Question 35

How many constant and variable regions are in the IgG heavy chain?

Answer 35

3 constant, 1 variable

Question 36

What is altered during isotype switching?

Answer 36

only the constant region of the heavy chain

Question 37

What do differences in the constant chains of Ab isotypes allow for?

Answer 37

versatility of anti-body mediated immune response

Question 38

What is different structurally in IgM and IgE from the other isotypes?

Answer 38

Have 4 constant regions and no hinge region

Question 39

IgM is always secreted as a ____

Answer 39

multimer (a pentameric form)

Question 40

What are the 5 copies of the immunoglobulin in IgM joined by?

Answer 40

J chain

Question 41

Each IgM molecule has (how many?) identical binding domains?

Answer 41

10

Question 42

IgA can be secreted as a _______

Answer 42

multimer (dimeric most important)

Question 43

What joins dimeric IgA?

Answer 43

J chain

Question 44

Which isotype has the longest half-life?

Answer 44

IgG

Question 45

Why are serum levels of IgE extremely low?

Answer 45

Rapidly bound up by mast cells

Question 46

Which isotype has the highest molecular weight?

Answer 46

IgM (b/c it is secreted as a pentamer)

Question 47

Which isotypes are important neutralizers?

Answer 47

IgG and IgA

Question 48

Which isotype(s) are important in opsonization?

Answer 48

IgG

Question 49

Which isotype functions in sensitization of mast cells?

Answer 49

IgE

Question 50

Which isotype is the most efficient activator of complement cascade?

Answer 50

IgM

Question 51

Which isotype most efficiently transports across epithelium?

Answer 51

IgA

Question 52

Which is the only isotype that transports across the placental barrier?

Answer 52

IgG

Question 53

Which isotype is the most important in diffusion into extravascular sites?

Answer 53

IgG

Question 54

What are the major functional regions of Abs?

Answer 54

Fc regions- binds to complement proteins and Fc receptors | Fab- contains antigen-binding sites (variable region)