Viruses are the small intracellular, parasitic organisms that are made up of strands of nucleic acids called RNA and DNA. All DNA viruses are double-stranded except the parvoviruses that are single-stranded. As noted on Page 735 of the study book, viruses are incapable of independent existence. All viruses have protein coats or capsids. A majority of the DNA viruses have envelopes while others do not have. Envelopes are the coverings of the viruses taken from the host cells plasma membranes as the viruses are budding off after attachment. Other strains of DNA viruses have spikes in their envelopes. Envelopes and spike are where there is a concentration of antigens. The non-enveloped viruses have only their protein coats. Viruses undergo a replication cycle. The morphology of a virus depends on its structure of the protein coat made up of units called protomers. Viruses have self-replication mechanisms using the host cell division apparatus. Viruses are also cellular or tissue-specific because of the cell receptor specificity in the spikes or envelopes. They are also sensitive to interferon.
The genetic constitution of DNA viruses is different from humans. The oncogene in a virus, after its attachment to the human host cell receptors that are specific for the virus, transform itself into the human DNA within the cell. This viral oncogene disrupts the normal human cell by converting it into a cancerous or dysfunctional cell. Other DNA viruses insert the oncogene on a particular site in the host cell genome causing cytolytic disruption or proliferation of normal cell cycles. Also, some do not insert but influence the cell division mechanisms of the host cell to produce abnormal cells. Thus, DNA viruses control and promote genetic expression in their hosts' cell. In their replication, viruses regulate gene expression, interact with the cell nucleus of the host, and show latency. Oncogenicity is about the DNA viruses being able to affect the normal functioning of any cell in the host by interfering with its nucleus. Overall, my understanding of why most DNA viruses are oncogenic is that except the poxviruses, replication of DNA viruses takes place in the core organelle of the host cell giving it the potency of transforming the genome to cancer cells.
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