In this viruses are lipid containing viruses whose genomes can act as mRNA. Most notorious of these is HIV and this viruses resulting in AIDS. Aside from HIV retroviruses are rather uncommon in humans, but prevalent in other mammals and birds. Genomes of retroviruses are similar in structure and size to picornaviruses like polio virus and one might suppose that the replicative strategy of a retrovirus resembles that of poliovirus. Life cycle of a retrovirus is unique and unusual
Plus strand of RNA is not associated with ribosomes, It has all the attributes of mRNA. Instead and virion RNA is used as a template to make a DNA copy of the viral genome. Copying of RNA into DNA is foreign for the host cell and must be carried out by a viral enzyme that is packaged in virion
The viral enzyme, called reverse transcriptase carries out this process. Terms reverse and retro imply a mechanism that is the opposite of that normally operating in all cells usual flow of information in a cell is from DNA to RNA is not from RNA to DNA. Initial product of reverse transcription is an RNA and DNA hybrid double helix
RNA portion of this hybrid is degraded and reverse transcriptase copies the remaining DNA strand into dsDNA. Processes take place in the cytoplasm. The viral dsDNA is synthesized, it is transported into the nucleus where it is inserted and covalently linked to Host chromosomal DNA. Viral DNA that is integrated into the host genome is called a provirus and it is indistinguishable from the host cell genes. The retrovirus has created a version of the viral genome that has all the attributes of a cellular gene found in the host. The integrated provirus can be transcribed by the host cell into (+) RNA that is transported to the cytoplasm and used either as mRNA in viral protein synthesis or as the genome for new progeny viruses
Plus strand of RNA is not associated with ribosomes, It has all the attributes of mRNA. Instead and virion RNA is used as a template to make a DNA copy of the viral genome. Copying of RNA into DNA is foreign for the host cell and must be carried out by a viral enzyme that is packaged in virion
The viral enzyme, called reverse transcriptase carries out this process. Terms reverse and retro imply a mechanism that is the opposite of that normally operating in all cells usual flow of information in a cell is from DNA to RNA is not from RNA to DNA. Initial product of reverse transcription is an RNA and DNA hybrid double helix
RNA portion of this hybrid is degraded and reverse transcriptase copies the remaining DNA strand into dsDNA. Processes take place in the cytoplasm. The viral dsDNA is synthesized, it is transported into the nucleus where it is inserted and covalently linked to Host chromosomal DNA. Viral DNA that is integrated into the host genome is called a provirus and it is indistinguishable from the host cell genes. The retrovirus has created a version of the viral genome that has all the attributes of a cellular gene found in the host. The integrated provirus can be transcribed by the host cell into (+) RNA that is transported to the cytoplasm and used either as mRNA in viral protein synthesis or as the genome for new progeny viruses
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