Viruses Chapter 19 Wow Are they alive???? Viruses are little more than genes packed into protein coats They lack the structures and metabolic activity found in most cells But they infect a host Cause a variety of diseases And can kill So it would be better to say they are in a nebulous state Not alive, not dead But instead living a borrowed life Structure Unlike bacteria Viruses cannot be cultured in media They need a host Not just nutrients The first isolated virus Was Tobacco Mosaic Virus Many viruses are smaller than a ribosome Millions can fit on a pin head Many viruses do not have the typical genome They can have double stranded DNA Single stranded DNA Single stranded RNA Double stranded RNA Can be called a DNA or RNA virus Depending on what it has