Microbiology

Microbiology Study Guide

Lysogenic Cycle It should be noted that all viruses may not replicate themselves by the lytic cycle of reproduction, but they may remain active in the host cells for a very long time without multiplying and growing. This process is known as lysogenic cycle, and such viruses are termed as provirus or temperate viruses. These viruses do not cause death to the host cells instantly. HIV virus is an example of temperate viruses. Retroviruses A retrovirus is an RNA enveloped virus belonging to the species of Retroviridae, which is duplicated in a host cell using the reverse transcriptase enzyme. It fosters the production of DNA. Using an integrase enzyme, this DNA is incorporated in the genome of the host cell. This will cause the virus to grow and replicate in the host cell using the DNA of the host cell. Unlike other viruses, in which protein is produced by translating DNA into RNA and then to protein, the function in a retrovirus is reversed. The DNA is formed from translating RNA that is united with the genome of the host cell that acts as a provirus. Finally, the genes of the virus are expressed by the normal processes of transcription and translation. A special variant of retroviruses is endogenous retroviruses, which are integrated into the genome of the host and inherited across generations. Effects of Viruses on Cells Isolation and Detection of Viruses Identifying viruses is not easy because viruses cannot be seen without an electron microscope. Western blotting (serology) is the most common way in which a virus is identified by its reaction to antibodies. Observation of cytopathic effects is also useful in the detection of viruses. Cytopathological Effects The visible effects of viral infections are known as cytopathic effects. Cytopathic effects are used to diagnose viral infections. They vary with the virus and at what point in the viral infection cycle they occur. The pathogenic properties of viruses depend on their ability to gain access to a host, evade the host’s defenses, and cause damage to the host cell while reproducing themselves. Transformation and Oncogenesis Several types of cancer are known to be caused by viruses. Anything that can alter the genetic material of a cell has the potential to make a normal cell cancerous. Cancer-causing viruses are called oncogenic viruses or oncoviruses. About 10% of cancers are known to be virus-induced. An outstanding characteristic of all oncogenic viruses is that their genetic material integrates into the host cell’s DNA and replicates along with the host cell’s chromosome. This can alter the host cell’s characteristics. Tumor cells undergo transformation, meaning that they develop distinct properties different from uninfected cells or from infected cells that do not make tumors. Transformed cells tend

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