There are problems with these three hypotheses and it is currently believed that virus particles are extremely ancient and pre-date the divergence of life into the three domains we use to define living things. Genetic analyses of virus particles have so far indicated that there is probably no single ancestral virus particle and that they sprung up several times in order to have multiple ancestral organisms, rather than just one. Prions are related to viruses but are not life at all because they don’t contain RNA or DNA. These are infectious protein molecules. There are many protein-prion diseases, such as “mad cow disease” or bovine spongiform encephalopathy, scrapie in sheep, chronic wasting disease in deer, kuru in humans, and Creutzfeldt-Jakob disease in humans. Whether or not viruses can be considered life is a matter of debate. They have genetic material and genes, they are known to evolve through natural selection, and can reproduce by creating multiple viral particles. They don’t, however, have a cellular structure or their own metabolism. They also don’t divide through mitosis and cell division but through the building up of their structure within a cell. They don’t, however, grow like crystal structures because they can inherit genetic mutations (and undergo natural selection).
VIRAL STRUCTURE Viruses have many different viral structures. Most are extremely small and cannot be seen via typical light microscopy. Many are between 20 and 300 nanometers in diameter; however, some are long and thin. As mentioned, they have a capsid or protein coat, which is made by different capsomeres or individual protein subunits. These capsomeres are made by the genetic material of the virus but require the protein-making structures of the cells that they infect. Some viruses will make proteins that assist in the making of their protein coat and other structures.
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