domain

Pronunciation: dō-mān′

Definition:

1. Homologous unit of approximately 110–120 amino acids, groups of which make up the light and heavy chains of the immunoglobulin molecule; each serves a specific function. The light chain has two domains, one in the variable region and one in the constant region of the chain; the heavy chain has four to five domains, depending on the class of immunoglobulin, one in the variable region and the remaining ones in the constant region.
2. A region of a protein having some distinctive physical feature or role.
3. An independently folded, globular structure composed of one section of a polypeptide chain. A domain may interact with another domain; it may be associated with a particular function. Domains can vary in size.

[Fr. domaine, fr. L. dominium, property, dominion]

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