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Antigen-antibody
HND Immunology
Question | Answer |
---|---|
What are the constituent parts of an antigen? | Epitope and carrier. |
What part of the antigen does the immune system recognise? | The epitope only. |
What name is given to an epitope isolated from an antigen? | Hapten. |
Are haptens immunogenic or antigenic? | Antigenic, not immunogenic as they are too small. |
How are haptens used during vaccinations? | Hapten is attached to carrier (non-immungenic carriers are preferable) immune cells and antibodies react with hapten alone, developing an immunity for the substance with certain epitope. |
What are the two common carrier molecules used with haptens? | Keyhole Limpet Hemocyanin (KLH). Bovine Serum Albumin (BSA). |
Describe KLH. | A large complex protein derived from shellfish making it large and foreign. Has a high molecular weight of 5000kD with lots of attachment sites fo peptide coupling which makes conjugation easy. |
What is one downside of KLH? | It is poorly soluble in water which restricts its practical applications. |
Describe BSA. | A plasma protein in cattle with a molecular weight of 67kD and is more soluble than KLH. |
Name a downside to BSA regarding immunoassays. | If an antibody used in the immunoassay was raised using a heptin and BSA complex then a false positive results may be recorded which could lead to a disease being incorrectly diagnosed. |
What are multiple antigenic peptides? | An immunogen composed of multiple copies of a single hapten attached to a polylysine core that provides a scaffolding, meaning that heptins can be synthesised directly onto the branching arms. |
Can multiple antigenic peptides be immunogenic? | Yes as it is a big enough molecule. |
What % of the total weight of MAP can heptins account for? | 95%. |
Where do epitopes recognised by B cells lie? | On the surface of the antigen. |
Where do epitopes recognised by T cells lie? | Inside the antigen, and so can only be accessed once the antigen has been processed. T cells do not recognise native antigens. |
Describe B cell epitopes. | Lie on the surface of the antigen they are composed of hydrophilic peptides and have a high degree of flexibility, may be continuous or discontinuous epitopes. |
What is the assortment of amino acids in a continuous epitope? | The amino acids lie together in both the primary and tertiary structure of the protein. |
What is the assortment of amino acids in a discontinuous chain? | The amino acids lie together in the tertiary structure but not the primary structure. |
Describe T cell epitopes. | The epitopes are found on the inside of the antigen tertiary structure, they are hydrophobic and tend to be continuous amino acid sequences. |
What type of bonds bind antigens and antibodies? | Hydrogen bonds. Electrostatic interactions (ionic bonds). Van der Waals forces. Hydrophobic interactions. |
What is critically important to the strength of the bonds between antigens and antibodies? | The distance between interacting groups. |
Why are weak bonds able to produce strong binding? | The large number of bonds created. |
How is the correct conformational shape produced by an antibody? and what effect does this have? | Using other amino acids in the antibody structure. This allows a close fit between the antigen and antibody. |
What is antibody affinity? | The strength of the bond between antibodies and antigens. |
What determines antibody affinity? | The sum of all non-covalent bonds between the antigen and antibody. |
Is antibody binding specific? | No, antibodies can bind several epitopes with different affinities. |
What is meant by specificity? | The ability of an individual antibody binding site to react with one epitope. |
What epitope features can antibodies often distinguish? | The primary structure. Secondary and tertiary structures. Isomeric forms. |
What is meant by cross reactivity? | The ability of an individual antibody binding site to react with more than one epitope. |
How do cross reactions arise? | Because the antigen has an epitope which is structurally similar to one found on another antigen. |
Can the same epitope exist on more than one specific antigen? | Yes, epitopes can be on the same or different antigens. |
Why is specific affinity more complex in the natural situation than on paper? | It is only the strength of the binding between an individual antibody binding site and a corresponding single epitope, so only measures the binding of an antibody with a simple antigen containing a single epitope. In real life, antigens have >1 epitope. |