RNA and DNA Viruses Reproduce in Cells

With the evolution of cells, carriers of DNA, organisms came to occupy all types of environmental niches. There is another niche—the cell itself. Here, DNA and RNA organisms live within cells to reproduce. These are the viruses. Viruses typically consist of a protein coat (nucleocapsid), encasing nucleic acid, RNA or DNA, with a membrane envelope with embedded proteins for enveloped viruses. Viruses are classified according to the type of nucleic acid and the way it is replicated in the cell. SARS-Cov-2 virus is an example of a (+) strand RNA virus. An example of a DNA virus is the monkeypox virus, a member of the poxvirus family. Another group of viruses with quite a different life cycle are the RNA (+) strand retroviruses, which replicate via a DNA intermediate. An example is the human immunodeficiency virus (HIV), which causes the acquired immunodeficiency syndrome (AIDS). A final example of an important human virus is the Ebola virus, which infects humans and other primates. This virus is an example of an RNA (−) strand virus. The plant virus considered is the alfalfa mosaic virus (AMV). All the four human viruses considered are enveloped viruses and have broad similarities in their life cycles in terms of entry, replication, and exit from the cell. However, their different nucleic acid biology provides important differences. Knowing the life cycle of the viruses provides the background for the therapeutic approach to the control of these serious human viruses. The therapeutic approaches considered are via vaccination and antivirals. For the plant, AMV virus genetic engineering methods are described.