Antibody Structure

Question 1

Whats then difference between plasma and serum?

Answer 1

Serum doesn’t contain clotting factors. Plasma does.

Question 2

What does electrophoresis do (general)?

Answer 2

separates proteins based on their net electrical charge. At pH 8.2 COOH turns to COO- and NH3+ turn to NH2 so the net electrical charge of most proteins is negative (they are anionic).

Question 3

Which node will proteins migrate towards if they are anionic (cathode or anode)?

Answer 3

anode.

Question 4

If you leave two Fabs joined on an antibody its called ____.

Answer 4

F(ab2)

Question 5

State whether the following are univalent, divalent, or variable valency: Fab, F(ab2), IgG

Answer 5

Fab- univalent (Fab is just one arm of the antibody) F(ab2)- divalent (This is just what its called when the two Fabs stay joined together. IgG- Divalent (a kind of antibody, it contains two Fab arms like normal antibodies).

Question 6

What is the Fc fragment and what is it composed of?

Answer 6

Fc is the base of the antibody (together with two Fabs fragments, it composes the antibody). The Fc is made of CH2 and CH3 regions.

Question 7

How many heavy and how many light chains in an antibody?

Answer 7

2 heavy (50000 MW) and 1 light (25000 MW).

Question 8

How do antibodies initiate inflammation?

Answer 8

By interacting with components of the complement system.

Question 9

Which domains does the light chain contain?

Answer 9

VL and CL (1 variable and 1 constant domain)

Question 10

Which domains does the heavy chain contain?

Answer 10

VH and CH1, CH2, CH3, (CH4)

Question 11

Draw and label a basic structure of IgG

Answer 11

Question 12

IgG is composed of what chains?

Answer 12

2 Light chains and 2 gamma chains (G for Gamma).

Question 13

IgD is composed of what chains?

Answer 13

2 light and 2 Delta (D for Delta). contains an extra long hinge region.

Question 14

IgE is composed of what chains?

Answer 14

2 light 2 epsilon (E for epsilon). Also contains an extra constant domain (E for Extra). The extra domain is CHE4 for a lot of sugars.

Question 15

IgM is composed of what?

Answer 15

It is a pentamer of a basic unit which is 2 light chains and 2 mu chains (M for mu). Has an extra domain (CHu4). It is linked by S-S bonds (like most antibodies) and has a J chain which closes the circle of 5 units on the pentamer.

Question 16

What is IgA composed of?

Answer 16

it is a dimer, where each monomer is composed of 2 light chains and 2 alpha chains (a for alpha). The two units are joined by a J chain and the whole thing is wrapped in secretory Component (IgA is secreted when it is used (in the gut)).

Question 17

Why do antibodies have rotational symmetry?

Answer 17

Because any given H or L chain is identical to the other H or L chains (respectively).

Question 18

L chains come in 2 varieties; what are they?

Answer 18

Kappa and Lambda

Question 19

True or false: When a cell switches from making IgM to IgA it will change the heavy chain from mu to alpha but the light chain will stay as a lambda.

Answer 19

True. But remember whether the light chain is lambda or kappa is determined by the cell. This is why it stays the same. If the cell started making IgM with kappa L chains then the new IgA would also have kappa L chains.

Question 20

What is another name for the hypervariable region and why is it hypervariable there?

Answer 20

The complementarity-determining regions or CDR. These are spots on the variable regions of both the heavy and light chains where most of the variation in the amino acids takes place. There are 3 hypervariable areas in each Variable region (L and H). These areas are where the antigen binds so they are variable to bind to different antigens with specificity.

Question 21

How many constant and variable domains are there?

Answer 21

one variable domain per chain (heavy or light) and one constant domain on the L chain with up to four on the H chain (Mu and Epsilon only have 4 the rest have 3).

Question 22

How many subclasses or isotypes of antibodies are there and how are they broken down

Answer 22

IgG1, IgG2, IgG3, IgG4

IgA1, IgA2

IgM1, IgM2

IgD

IgE

Question 23

Descibe what allotypes are.

Answer 23

The minor allelic differences in the sequence of immunoglobulins between individuals. This is similar to how there are differences that determine eye color and blood type.

Question 24

The unique structure which makes up the CDR AAs on the L and H chains is called ______

Answer 24

an idiotype.

Question 25

what is an anti-idiotype?

Answer 25

an antibody which recognizes and binds the CDR on an antibody. Thus, we come to think of an idiotype, or an antibody’s unique set of CDRs, as an antigen.

Question 26

What is the most common antibody in the serum?

Answer 26

IgG, Then IgA, IgM, IgD, IgE. Goes in order of decreasing subtypes.

Question 27

What is the importance of the five types of antibodies?

Answer 27

IgG- main antibody in blood and tissues. Neutralizes toxins and blood-borne viruses. Binds bacteria and then destroys them by activating complement and having them bound to phagocytic cells

IgA- does similar stuff in the blood as IgG. Main role is as a dimer in secretions. Secretory Component protects this antibody from proteolysis.

IgM- Similar to IgG but is bigger, very efficient at activating complement (because only one is necessary) however, it does not get into the tissues very easily. It is not bound by phogocytes.

IgD- receptor on B cells (not that important)

IgE- causes Type I immunopathology. Functions in resistance to worms and parasites.

Question 28

describe the allosteric effect of an antibody

Answer 28

when IgG or IgM bind to an antigen, there is a change in angle between the Fab and the Fc. This change causes a

conformational change in the Fc region.

Question 29

A change in the Fc region (induced by the binding of an antigen to IgM or IgG) causes what?

Answer 29

One of a couple things:

1. binding to a phagocytic cell (especially PMNs, Eosinophils, and macrophages). These have FcRs for the altered Fc region.
2. activate compliment by binding to C1q. Remember that for IgG this requires two antibodies to be bound to antigen which have the conformational change in the Fc and can then bind to C1q at the same time. For IgM this only requires one antibody because binding of an antigen at any of the 5 sites causes a conformational change in all of the Fc regions.