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Flashcards in Antibody Structure Deck (20)
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1

What is the order of bands produced when serum is separated by electrophoresis?

Albumin, alpha-1, alpha-2, beta-1, beta-2, gamma

2

What is macroglobulin?

Macroglobulin is an antibody with a 900,000 MW, as opposed to gamma globulin's 150,000 MW.

3

What are the Fab and Fc regions, and light and heavy chains?

The Fab region is the combination of the variable regions of the antibody, consisting of a portion of the heavy chain and the entirety of the light chain.  There are 2 Fabs on each antibody.   The heavy chains are the longer polypeptides that consist of variable and extended constant regions, light chains contain variable and short constant regions.

4

What is F(ab2) and how is it different from Fab?

F(ab2) is created by altering the restriction point on the antibody (using a different enzyme) to produce a single  protein product that contains both antigen binding regions.   F(ab2) is divalent, whereas Fab is univalent because it only contains one binding region (though there would be twice as much Fab as F(ab2) from the same sample). 

5

What domains do light and heavy chains contain, and what holds them together?

Both light and heavy chains are cunstructed of variable and constant domains, and are connected to each other by sulfide bonds (S--S).   The light chains have one variable and one constant domain each, while the heavy chains have one variable and 3-4 constant domains each.

6

Which immunoglobulins are actually multimers?

All immunoglobulins are constructed of pairs of 2 heavy chains and 2 light chains.   IgA and IgM, however, are actually multimers of immunoglobulins.  IgA is a dimer, IgM is a pentamer, both have J-chains connecting their Ig substituents.   IgA is further covered in Secretory Component.   All Igs (alpha, delta, gamma, epsilon, & mu) are defined by their heavy chains, which determine their polymerization and biological properties.

7

What are Kappa and Lambda chains?

Kappa and Lambda are the two varieties of light chains.      A cell may produce either of the varieties, but once it produces one it will never produce the other.   Thus, if the cell undergoes class switching (from producing IgM to IgG, say), it will NOT switch light chains.   It will only continue to produce the same light chain, 

8

What is the CDR and what does it do?

The CDR is the Complimentarity-Determining Region.   Also called the Hypervariable region beacuse it is the most variable portion of the variable region.   It is the region of the Ig molecule which actually binds to the antigen.   The CDR is the antigen binding site.

9

What does "valence" mean in terms of Ig molecules, and what is the valence of IgG, IgA, IgM, Fab and F(ab2)?

Valence refers to the number of antigens an Ig molecule may bind to.   The valence of IgG = 2, IgA = 4, IgM = 10, Fab = 1, and F(ab2) = 2.

10

What are subclasses or iostypes, and how many are there of each Ig class?

Subclasses (isotypes) are variants of the five main Ig classes.   There are four IgG isotypes (IgG1-4), two IgA (IgA1&2), two IgM (IgM1&2), and only one type of IgD and IgE.   Isotypes/subclasses are NOT different alleles.

11

What are Ig allotypes?

Allotypes are actual allelic differences between individuals, unlike isotypes.   Allotypes are heritable and can be used to determine relatedness of individuals and in forensic medicine.

12

What are idiotypes and anti-idiotypes?

An idiotype is the specific sequence of the V(D)J, hypervariable region, individual to that antibody-producing cell.   An anti-idiotype is an antibody that is created (likely in another species) that is specific to that particular idiotype.   The idiotype (normal antibody) would play the role of antigen to the anti-idiotype.

13

What are the normal concentrations of each class of Ig in serum?

IgG = 1000 mg/dl; IgA = 200 mg/dl; IgM = 100 mg/dl; IgD = 5 mg/dl; IgE = 0.02 mg/dl.   Note: IgG is 10x more concentrated than IgM

14

What is the structure and function of IgG?

IgG is the main antibody in blood and tissue fluids.   It neutralizes toxins.   It binds bacteria and facilitates their destruction by activating complement and by helping phagocytic cells bind them.   It is constructed of two light chains and two gamma heavy chains with three constant (HC) regions.

15

What is the structure and function of IgE?

IgE is important in resistance to parasites (worms, e.g.). It is also the antibody that causes Type 1 Immunopathology, which is immediate hypersensitivity or allergy.   It is composed of two light chains and two epsilon heavy chains with four constant (HC) regions.

16

What is the structure and function of IgA?

In the blood, IgA functions similarly to IgG, but its real role is as the dimer form in secretions, where its Secretory Component protects it from proteolysis.   IgA is a dimer of two sets of light chains and two sets of alpha heavy chains, with three constant regions (HC), a J-chain, and secretory component.

17

What is the structure and function of IgM?

IgM functions much like IgG.   It is the first antibody to appear in the serum after immunization, and it is very efficient at activating compliment.   However, its large size prevents it from getting into tissue fluids efficiently.   It is a pentamer composed of five fully formed, mu heavy chain antibodies and one J chain.

18

What is the structure and function of IgD?

IgD functions as a cell surface receptor on B cells.   It is composed of two light chains and two delta heavy chains with three constant regions (HC) and an extra long hinge region.

 

19

What happens when an IgG or IgM binds to an antigen?

Binding of an IgG or IgM to an antigen causes a conformational change in the hinge region of the Ig molecule which then causes a bulging of the Fc region.     If IgG is bound, this conformational change leads to the binding of PMNs, eosinophils, and macrophages which have receptors (FcR) for the IgG (but NOT IgM).   The conformational shift also triggers the binding of C1q, the first protein of the complement sequence, but only if there are two adjacent, bound Igs.  This is why IgM is so effective at activating compliment as it always has five available Fc regions for C1q binding.

20

What are the two basic steps of antigen-antibody interactions?

The first step is antibody BINDING/RECOGNITION, the second step is the antibody actually DOING SOMETHING such as crosslinking antigen molecules, activating complement, or binding to a phagocyte.