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It is the first step of viral replication. Some viruses attach to the cell membrane of the host cell and inject its DNA or RNA into the host to initiate infection. Attachment to a host cell is often achieved by a virus attachment protein that extends from the protein shell (), of a virus.
Viruses are a particularly effective form of gene delivery because the structure of the virus prevents degradation via lysosomes of the DNA it is delivering to the nucleus of the host cell. [28] In gene therapy a gene that is intended for delivery is packaged into a replication-deficient viral particle to form a viral vector . [ 29 ]
5' small nucleolar RNA capped and 3' polyadenylated long noncoding RNA - SRP RNA: signal recognition particle RNA CL00003: ssRNA single stranded RNA - stRNA: small temporal RNA - tasiRNA: trans-acting siRNA - tmRNA: transfer-messenger RNA RF00023: Bacterial RNA molecule with dual tRNA-like and messenger RNA-like properties uRNA U spliceosomal ...
The virus then releases its genetic material (either single- or double-stranded RNA or DNA) into the cell. In some viruses this genetic material is circular and mimics a bacterial plasmid . At this stage the cell becomes infected and can also be targeted by the immune system.
Reverse transcribing viruses replicate their genomes by reverse transcribing DNA copies from their RNA; these DNA copies are then transcribed to new RNA. Retrotransposons also spread by copying DNA and RNA from one another, [ 66 ] and telomerase contains an RNA that is used as template for building the ends of eukaryotic chromosomes .
RNA viruses generally have very high mutation rates compared to DNA viruses, [8] because viral RNA polymerases lack the proofreading ability of DNA polymerases. [9] The genetic diversity of RNA viruses is one reason why it is difficult to make effective vaccines against them. [ 10 ]
Translation is accomplished by the ribosome, which links proteinogenic amino acids in an order specified by messenger RNA (mRNA), using transfer RNA (tRNA) molecules to carry amino acids and to read the mRNA three nucleotides at a time. The genetic code is highly similar among all organisms and can be expressed in a simple table with 64 entries.
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.