Structural motif
In a chain-like biological molecule, such as a protein or nucleic acid, a structural motif is a common three-dimensional structure that appears in a variety of different, evolutionarily unrelated molecules. A structural motif does not have to be associated with a sequence motif; it can be represented by different and completely unrelated sequences in different proteins or RNA. == In nucleic acids == Depending upon the sequence and other conditions, nucleic acids can form a variety of structural motifs which is thought to have biological significance.