- In biomedicine, a domain is a discrete portion of a protein with its own function. The combination of domains in a single protein determines its overall function. (Not to be confused with an Internet domain.)
* * *1. Homologous unit of approximately 110–120 amino acid s, 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 upon 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 d. may interact with another d.; it may be associated with a particular function. Domains can vary in size. [Fr. domaine, fr. L. dominium, property, dominion]
* * *do·main dō-'mān, də- n1) any of the three-dimensional subunits of a protein that together make up its tertiary structure, that are formed by folding its linear peptide chain, and that are variously considered to be the basic units of protein structure, function, and evolution <immunoglobulin light chains have two \domains and heavy chains have four or five \domains, depending on class (Jour. Amer. Med. Assoc.)>2) the highest taxonomic category in biological classification ranking above the kingdom
* * *do·main (do-mānґ) 1. an area or region that is defined or delimited in some way. 2. a compact globular structure composed of one section of a polypeptide chain that constitutes a recognizable unit of the tertiary structure of a protein. Domains may fold up independently and maintain their native conformation when the connecting sections of the chain are broken. 3. one of the three broad divisions into which all living organisms may be classified: the Archaea, the Bacteria, and the Eucarya; the first two consist of the prokaryotes, whereas the last contains the eukaryotes. This system is an alternative to the traditional five-kingdom classification (see kingdom).
Medical dictionary. 2011.