Viruses are made up of genetic material (DNA or RNA12) encased in a protective protein coat. They are only capable of multiplying using infected cells, and need the infected cell’s molecular machinery in order to replicate their genetic material and the viral coat proteins that make up the protein coat.
There is a great variety of different kinds of virus. Some infect animals, others infect plants or bacteria. Plant viruses are either rod-shaped (like the papaya ringspot virus) or spherical. They show great variation in size but the largest plant viruses are still extremely small (one thousandth of a millimeter).
During a typical infection process of an animal or bacterial cell the virus attaches itself to the cell in order to inject its genetic material or to fuse with the host cell. Plant cells on the other hand have sturdy cells walls that plant viruses cannot penetrate without help. For this reason plant viruses are generally transferred when damage has been caused by other organisms, such as aphids. The first step in infection is the uncoating of the virus.13 A few dozen coat proteins are removed from one side, partly exposing the genetic material. The plant’s ribosomes recognize this genetic material. Ribosomes are specialized deciphering machines that can translate the message that is hidden in the virus’ genetic material into the production of proteins. While the ribosomes are translating the virus’ genetic material, the virus continues uncoating.13 In this way new coat proteins and other proteins necessary for the virus’ multiplication are made. The virus effectively puts the infected cells to work making new virus particles. Once the virus’ genetic material has multiplied sufficiently and enough coat protein has been synthesized, the genetic material is recoated by the coat proteins. The newly formed virus particles then infect new cells and if the infection is not stopped this can lead to the eventual death of the host organism.