Exam 1 (Lecture 6) - Antibodies and Antigens Flashcards
Draw an antibody molecule (immunoglobulin) and label:
1) Heavy chain - VH, CH1, CH2, and CH3 - list the different types of heavy chains
2) Light chain - VL, CL, - list the different types of light chains
3) Constant portion
4) Variable portion
5) Fab
6) Fc
7) Antigen binding site
8) Hinge region
9) Domains/homology (how many AAs in a domain)?
10) Portion important in biological activities like complement fixation, opsonization
1) Heavy chain types: M, D, G, E, A
2) Kappa and lambda
3)
4)
5) Fab: fragment antigen-binding site
6) Fc: dictates biological activity
7) Antigen-binding site: consists of variable portions
8) Hinge region: gives flexibility; contains disulfide bonds
9) About 110 AAs that fold into loops help by disulfide bonds
Define antigen, immunogen, and epitope.
1) Antigen = Molecule that binds to an antibody/T cell receptor/B cell receptor
2) Immunogen = Antigen that induces an immune response
3) Epitope = Specific portion of macromolecular antigen to which an antibody binds
Describe the types of bonds that form between antigens and antibodies and give a couple of examples.
Non-covalent bonds.
- Electrostatic = attraction between opposite charges
- Hydrogen bonds = hydrogen shared between electronegative atoms
- van der Waals forces = electron cloud sharing
- Hydrophobic bonds = Ag-Ab bind and exclude water
- Cation-pi interaction = interaction between cation and electron cloud of nearby aromatic group
List and briefly explain the general properties of antigen-antibody binding.
1) Reversible - bind and unbind; higher affinity will increase the time that antigen and antibody are bound
2) Goes to equilibrium
3) Rapid (depending on temperature); at low temps binding is slower; but at very high temps denaturing can occur
4) Dependent on pH and ionic strength
Draw and explain using an example of how antibody-antigen binding is reversible and goes to equilibrium.
If a tube has bacteria with all antibody sites bound and no excess antibodies are present, equilibrium will occur. If more bacteria is added (without more antibodies), antibodies will unbind the bacteria and equilibrate until all bacteria have the same number of antibodies bound.
Using affinity chromatography, draw and explain the steps to purify: a) a virus b) an IgG antibody to a specific virus. Correctly decide if one or two columns are needed to purify the requested material.
1) Virus = 1 column needed
- add antibody to column with insoluble beads to bind together
- add solution with mixture of antigens
- only antigen specifically desired should bind and the rest filter out
- dispose of unbound antigen
- collect antigen by changing pH and isotonicity to break non-covalent bonds between Ag and Ab
2) IgG specific to virus = 2 columns needed
- See picture
Describe the characteristics of a good antigen/immunogen (ie the important properties of a good antigen).
1) Foreignness - tolerance to self is induced in fetus so good antigens are not present during fetal development
2) Size - larger than 10,000 MV is best as small molecules don’t stimulate immune response
3) Molecular complexity - (ex: proteins) more charges, more hydrophobic areas
4) Rigidity/degradability - structure is needed so that the antibody can bind; if antigen is undegradable or too easily degradable, an immune response will not occur
Define hapten and carrier. Briefly explain what you expect from a response to a hapten alone and to the hapten-carrier and reasons for the difference. Give an example of a clinically relevant situation of hapten-carrier complex.
Hapten = Small molecule that will not create an immune response.
Carrier = Large protein that will covalently bind to hapten.
Hapten-Carrier Complex = The small molecule and protein binding together that allows an immune response to occur.
Example: Penicillin Allergy
- Penicillin is a small non-immunogenic molecule. In some individuals, it’s products will be broken down and covalently
bind to carrier proteins. The penicillin-carrier complex is large and complex for binding. The penicillin is considered
foreign so the complex becomes immunogenic.
Explain how and when an antibody can be an antigen.
Antibodies can become antigens when they are injected into different species. Antibodies are large protein structures that when in another species are foreign. So, an immune response will occur. This is referred to as serum sickness.
Define anti-immunoglobulin.
An antibody that is produced in response to an antibody from another species. (An antibody to an antibody).
