A virus particle has thus been defined as a structure which has evolved to transfer nucleic acid from one cell to another a The nucleic acid found in the particle is either DNA or RNA, is single-or double-stranded and linear or segmented. In some cases the nucleic acid may be circular. A virus particle has thus been defined as a structure which has evolved to transfer nucleic acid from one cell to another.  The nucleic acid found in the particle is either DNA or RNA, is single- or double-stranded and linear or segmented. In some cases the nucleic acid may be circular