Viruses consist of strands of the genetic material nucleic acid—either as RNA or DNA, but not both—surrounded by a protein coat called a capsid. The capsid protects the genome (collection of genes); it is often subdivided into individual protein particles called capsomeres—features that create the shape of the virus. The capsid protein coat of a virus can come in three main shapes: Helical, resembling a wound spring (such as the tobacco mosaic virus); isosahedral, a multifaceted virus (such as the herpes simplex); and complex, as the name implies, can be combination of shapes (such as T-4 bacteriophage).