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In some species of RNA virus, the genes are not on a continuous molecule of RNA, but are separated. The influenza virus, for example, has eight separate genes made of RNA. When two different strains of influenza virus infect the same cell, these genes can mix and produce new strains of the virus in a process called reassortment. [33]
Some viruses may have evolved from bits of DNA or RNA that "escaped" from the genes of a larger organism. The escaped DNA could have come from plasmids (pieces of naked DNA that can move between cells) or transposons (molecules of DNA that replicate and move around to different positions within the genes of the cell). [11]: 810 Once called ...
Some viruses may have evolved from bits of DNA or RNA that "escaped" from the genes of a larger organism. The escaped DNA could have come from plasmids (pieces of naked DNA that can move between cells) or transposons (molecules of DNA that replicate and move around to different positions within the genes of the cell).
Remarkably, the capture of syncytin or syncytin-like genes has occurred independently, from different groups of endogenous retroviruses, in diverse mammalian lineages. Distinct, syncytin-like genes have been identified in primates , rodents , lagomorphs , carnivores , and ungulates , with integration dates ranging from 10 to 85 million years ago.
All living cells contain both DNA and RNA (except some cells such as mature red blood cells), while viruses contain either DNA or RNA, but usually not both. [15] The basic component of biological nucleic acids is the nucleotide, each of which contains a pentose sugar (ribose or deoxyribose), a phosphate group, and a nucleobase. [16]
Viruses may undergo two types of life cycles: the lytic cycle and the lysogenic cycle. In the lytic cycle, the virus introduces its genome into a host cell and initiates replication by hijacking the host's cellular machinery to make new copies of the virus. [12] In the lysogenic life cycle, the viral genome is incorporated into the host genome.
For the virus to reproduce and thereby establish infection, it must enter cells of the host organism and use those cells' materials. To enter the cells, proteins on the surface of the virus interact with proteins of the cell. Attachment, or adsorption, occurs between the viral particle and the host cell membrane.
The tumor virus can introduce and express a "transforming" gene either through the integration of DNA or RNA into the host genome. The tumor virus can alter expression on preexisting genes of the host. One or both of these mechanisms can occur in the same host cell.