Answer the questions below as completely and as thoroughly as possible and where

Question

Answer the questions below as completely and as thoroughly as possible and where appropriate include a specific example to illustrated. Answer the question in essay form (not as an outline or as bullets) using complete sentences. You may use diagrams to supplement your answers, but a diagram alone without appropriate discussion will not be adequate for full credit. Cite sources of information you used to answer the questions or that support your answer.

25. List the stages of the viral life cycle (see Course Module 4) and briefly describe the principal events in the stages of the life cycle of a virus in the Retroviridae family and explain what makes viruses in that family difficult to eliminate from the host. Name a virus in that family.

Note: Please read all the instructions especially the part about providing a complete and proper citation of where you got your information for the question before answering #25.)

Explanation / Answer

Retroviridae is a family of enveloped viruses that replicate in a host cell through the process of reverse transcription. A retrovirus is a single-stranded positive-sense RNA virus with a DNA intermediate and, as an obligate parasite, targets a host cell. Once inside the host cell cytoplasm, the virus uses its own reverse transcriptase enzyme to produce DNA from its RNA genome — the reverse of the usual pattern, thus retro (backwards). This new DNA is then incorporated into the host cell genome by an integrase enzyme, at which point the retroviral DNA is referred to as a provirus. The host cell then treats the viral DNA as part of its own genome, translating and transcribing the viral genes along with the cell's own genes, producing the proteins required to assemble new copies of the virus. It is difficult to detect the virus until it has infected the host. At that point, the infection will persist indefinitely.

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