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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]
Where DNA or RNA which that has been packaged as part of a virus particle, but may not necessarily contain any viral genes, becomes integrated into a hosts genome this process is known as transduction. Maintenance of the viral genome within host cells but not as an integrated part of the host's genome.
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).
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.
The first man-made infectious viruses generated without any natural template were of the polio virus and the φX174 bacteriophage. [4] With synthetic live viruses, it is not whole viruses that are synthesized but rather their genome at first, both in the case of DNA and RNA viruses. For many viruses, viral RNA is infectious when introduced into ...
However, some DNA phages such as T4 may have large genomes with hundreds of genes; the size and shape of the capsid varies along with the size of the genome. [73] The largest bacteriophage genomes reach a size of 735 kb. [74] Schematic view of the 44 kb T7 phage genome. Each box is a gene. Numbers indicate genes (or rather open reading frames).