Quinternary structures

The secondary structures are combined with specific geometric arrangement to form compact globular structure known as tertiary structure. The fundamental unit of tertiary structure is the domain, which is defined as a polypeptide chain or a part of a polypeptide chain that can independently fold into a stable tertiary structure (Murphy, 2001). Domains are also units of function, and often the different domains of a protein are associated with different functions. Polypeptide chains, especially of regulatory proteins, often aggregate by specific interactions to form oligomeric structures. These oligomeric proteins are said to exhibit quarternary structure. The association of proteins with other biomacromolecules to form complexes of cellular components is referred to as quinternary structure. 

Quinternary structure (5° structure) refers to the association of one class of biomacromolecule with another class of biomacromolecule to form complexes of cellular components such as histone (DNA-protein), ribosome (RNA-protein) and glycoprotein (oligosaccharide-protein). 

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