Structure
Antibodies are heavy (~150 kDa) globular plasma proteins. They have sugar chains added to some of their amino acid residues. In other words, antibodies are glycoproteins. The basic functional unit of each antibody is an immunoglobulin (Ig) monomer (containing only one Ig unit); secreted antibodies can also be dimeric with two Ig units as with IgA, tetrameric with four Ig units like teleost fish IgM, or pentameric with five Ig units, like mammalian IgM.
The variable parts of an antibody are its V regions, and the constant part is its C region.
Read more about this topic: Surface Immunoglobulin
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—Ovid (Publius Ovidius Naso)