antibody structure and function

Question 1

why are antibodies also called globular proteins and immunoglobulins?

Answer 1

because they are large glycoproteins based on their tertiary and quaternary structure have globular confirmation

Question 2

what is the simplest antibody composed of?

Answer 2

4 peptide chains with an amino and carboxyl end bound together by disulfide bonds

Question 3

what are the Fab regions of the antibody?

Answer 3

amino ends of the polypeptide sites

Question 4

what is in the Fc region of the antibody?

Answer 4

carboxyl ends of the peptides

Question 5

what are the two forms of light chains?

Answer 5

lambda and kappa ends

Question 6

true or false: Since the chains are identical on an antibody molecule, an antibody will contain either forms of the light chains

Answer 6

true

Question 7

what proteolytic enzyme was Porter working with?

Answer 7

papain

Question 8

what does papain chemically digest an antibody molecule into and the significance of it?

Answer 8

3 proteins

Two of them were able to still bind antigen epitope and labeled them Fragment antigen binding (Fab) and the last could be crystalized out of solution (Fc).

Question 9

what can digest the antibody molecule in to a divalent fragment (F(ab’)2) and numerous Fc
smaller fragments?

Answer 9

endopeptidase pepsin

Question 10

what part of the antibody determines the antigenic epitope specificity of each antibody?

Answer 10

the 2 light polypeptide chains and 2 heavy polypeptide chains of the V regions

Question 11

what impacts the structural conformation of the regions of 2 light polypeptide chains and 2 heavy polypeptide chains (V regions)?

Answer 11

they have a high degree of variability of amino acid sequences

Question 12

true or false: for each antibody the 2 heavy
polypeptide chains and the 2 light chains are different to each other.

Answer 12

false: identical

Question 13

why is the C region called the constant regions?

Answer 13

the light polypeptide chains and heavy chains contain relatively conserved amino acids for the individual

Question 14

what is the purpose of the hinge region?

Answer 14

provide flexibility to the antibody molecule aiding in its function

Question 15

antibodies can be bound to the surface of B cells as a component of the B cell receptors (BCR) coupled with a ____________________________ to form the B cell receptor complex

Answer 15

surface heterodimer protein Igα/Igβ

Question 16

when antibodies exist as a secretory protein, where can they be found?

Answer 16

secretions, intracellular spaces, and blood vascular

Question 17

true or false: each antibody has specificity for a particular antigenic epitope

Answer 17

true

Question 18

what is the specificity of the antibody conserved for?

Answer 18

all the BCRs on that specific B cell and all the antibodies that are produced by that specific B cell

Question 19

what is the hypervariable regions of the antigen-antibody binding (Fab) region?

Answer 19

complimentary determining regions (CDRs) in which the amino acids in these regions are unique per antibody

Question 20

what is the result of the substitution of the amino acids in the CDR?

Answer 20

alter the structural conformation of the antibody binding site and thus, the antigenic epitope that it can recognize

Question 21

what solely defines the conformational groove that recognizes a specific epitope structure?

Answer 21

based on the interaction between the amino acid sequences in the hypervariable regions or CDRs of the heavy chain with the CDRs of the light chain

Question 22

what is the outcome of the hypervariable region?

Answer 22

each naïve B cell can create an antibody with a
unique antibody binding site capable of recognizing a unique antigen epitope

Question 23

what does the cysteine contain that forms the disulfide bonds between the peptide chains?

Answer 23

reactive sulfhydryl groups

Question 24

the hinge region of the heavy chains allow for what?

Answer 24

flexibility for optimal binding to multiple antigens expressing the same epitope

Question 25

what is the purpose of proline?

Answer 25

serves to prevent globular folding to contribute to diverse biological activity of the glycoprotein

Question 26

since the Fc region is the site for the biologic activities of the antibody molecule, in order to prevent premature biologic activity, the Fc region is folded in to the ____________________

Answer 26

secretory antibody

Question 27

what happens once the secretory antibody binds antigenic epitope via antigen binding?

Answer 27

the antibody undergoes a confirmation change causing the Fc portion to be position outward, similar to a flag so the antibody can participate in its designate biologic activity

Question 28

what is the first step in order for antibodies to perform biological activity?

Answer 28

they first have to recognize their cognate antigen epitope and bind to it

Question 29

what is agglutination?

Answer 29

crosslinking to create aggregates ex. RBCs + antibody = agglutination

Question 30

what is are examples of a diagnostic testing that uses the principle of agglutination?

Answer 30

- ABO blood typing test in humans - coombs test used to evaluate hemolytic disease of newborn or immune-mediated hemolytic anemia

Question 31

what is opsonization?

Answer 31

coating of antigen with secretory antibodies allowing it to be more efficiently phagocytosed

Question 32

what makes the phagocytosis of the antigen more efficient in regards to the Fc region during opsonization?

Answer 32

upon binding to antigen epitope, the antibody molecule undergoes a conformational change allowing the Fc region to be fully extended allowing it to be bound by cells expressing a receptor (Fc receptor)

Question 33

what is neutralization?

Answer 33

the process in which antibodies bind to an organism (i.e. flagella or cilia of a bacteria) or toxin (i.e. tetanus, botulinus, snake venom) and block its activity

Question 34

what is an example of a diagnostic testing using neutralization?

Answer 34

virus neutralization assay- to detect the presence of host neutralizing antibodies in patients to select viruses like COVID-19

Question 35

what is precipitation?

Answer 35

process in which antibodies bind to *soluble antigens* causing them to clump and form a visible precipitate

Question 36

how are precipitation and agglutination similar?

Answer 36

mechanism of action in that the antibodies cross link the epitopes on different antigens

Question 37

what is the difference between precipitation and agglutination?

Answer 37

the target antigen is soluble and not particulate

Question 38

what is an example of a diagnostic testing using precipitation?

Answer 38

immunodiffusion assays- to detect the presence of soluble antigen

Question 39

what are complement proteins?

Answer 39

collection of innate proteins that are continuously produced in the body as they tend to degrade rapidly

Question 40

what is the purpose of complement activation?

Answer 40

when the complement proteins are activated, they can significantly ramp up the immune response

Question 41

true or false: some of the byproducts of complement pathways can function as opsonins

Answer 41

true

Question 42

what is the result of antibodies (IgG) activating complement via classical pathway?

Answer 42

lysis of target cell

Question 43

what does it mean when the CDRs in the VL and VH regions form the antigen-antibody binding site based the interaction of the amino acid residues?

Answer 43

the binding of epitope in the antigen groove (binding site) is weak and noncovalent

Question 44

when the binding of an epitope is weak and noncovalent, what does this suggest?

Answer 44

weak binding could allow antibodies to be recycled

Question 45

why does antigen epitope recognition and binding have to be tight?

Answer 45

it reinforces the concept of antigen specificity

Question 46

What do the evaluation of antibody titers tell us about an individual?

Answer 46

it is a type of blood test that determines the presence and level (titer) of antibodies in the blood. This test is carried out to investigate if there is an immune reaction triggered by antigens in the body.