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AB & AG - Coggle Diagram
AB & AG
antibodies
special proteins produced by the immune system of animals as specific defence against attack of foreign intruders
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MONOCLONAL
are produced by identical immune cells
that are all clones of a unique parent cell. Monoclonal antibodies bind only to one epitope of the antigen.
- Monoclonal antibodies are highly specific
- Monoclonal antibodies provide more reproducible results since they are highly homogenous
POLYCLONAL
normally generated by B cells of animals inoculated repeatedly with the AG.
- Polyclonal antibodies can recognise multiple epitopes and, therefore, are less sensitive to small changes in the structure of the antigen or to its partial denaturation
- Polyclonal antibodies can be produced by different species of animals (e.g. rabbit, mouse, goat, sheep, donkey and chicken) providing a variety of options
an AB is a glycoprotein
namely an immonoglobuline Ig
constituted of polypeptides and sugar.
Y-shaped immunoglobulin (Ig) consisting of two identical heavy chains (H) and two identical light chains (L) connected via disulphide bridges.
The polypeptide chains start with the Nterminus on the arms of the Y, while the C-terminus are directed towards the basis of the stem of the Y.
Each chain consists of homologous units, composed of variable (V) or constant (C) regions.
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Cleaving of an immunoglobulin by papain, resulting in two identical Fab fragments and one Fc fragment.
antigen
any substance or functional group, which characterises the intruder, that induce the production of specific antibodies able to recognise and eliminate that intruder
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vaccines: an AG is inoculating in a living organism to induce the production of AB for that specific AG
haptens: antigen that are small molecules (MW<10 kDa) able to induce the production of specific AB when bound to a carrier with higher MW, typically a protein
INTERACTION
The interactions between antibody paratopes and antigen epitopes are based on:
- hydrogen bonding
- ionic and hydrophobic interactions
- Van der Waals forces
Individually, these interactions are weak and reversible; however, the cooperation of more than one effect at the same time significantly strengthens the binding between AB and AG
factors influencing AG-AB interaction:
- time
- temperature
- pH
- ionic strenght
Affinity is a measure of the strength of the interaction between a single epitope and paratope. The affinity is defined by the association constant Ka.
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The avidity quantifies the overall strength of the Ag–Ab interaction. It depends on 3 factors:
- the paratope–epitope affinity
- the valence of the antibody and antigen
- the structural arrangement between the interacting parts
Affinity and avidity are both measures of binding strength. While affinity is the measure of the binding strength at a single binding site, avidity is a measure of the total binding strength.
The specificity of an Ab is defined as its capability to react only with one specific antigen. The specificity depends on the affinity more than on the avidity
Cross-reactivity indicates the ability of an individual antibody to react with more than one antigen. Of course, polyclonal AB has high cross-reactivity
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