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Retrovirus Contain RNA, not DNA. Family Retroviridae Contain enzyme called Reverse Trascriptase When a retrovirus infects a cell, it injects its RNA and reverse trancriptase enzyme into the cytoplasm of that cell. The enzyme reverse transcriptase, which causes synthesis of a complementary DNA molecule using virus RNA as a template. HIV,   the AIDS ( Acquired Immune Deficiency Syndrome) virus is a retrovirus. The retroviridae family encompasses a group of viruses in which the replicative life cycle requires reverse transcription of the viral ribonucleic acid (RNA) genome into doublestranded deoxyribonucleic acid (DNA). In fact, discovery of the enzyme that performs this task, reverse transcriptase, revolutionized the understanding of genetic structure and produced the enzymatic tools used in all modern molecular biology laboratories to study the structure of messenger RNA (mRNA) and evaluate gene expression. Retroviridae initially were identified in a variety of...

— The term “ lysogenic ” implies that prophages are capable of giving rise to active phages that lyse their host cells. This occurs when the viral genome exits the bacterial chromosome and initiates the lytic cycle. The triggers for this switch-over are usually environmental factors such as mutagens (e.g. radiation and presence of certain chemicals) — It depends on a few factors, such as how many phages infected the cell, whether or not the cell is in good growth conditions, and so on. — If the cell is in stress or has low amounts of nutrients, the lysogenic pathway is typically activated. — The underlying mechanism has to do with a protein cascade involving either the cro or cI protein that is encoded by the virus. — The cI protein is a repressor, and it will prevent the lytic genes from being transcribed. By default the virus will transcribe the lytic genes, so they must be repressed for lysogeny to occur. — Similarly, cro is also a transcriptional repressor....

Viruses A viruses is a non-cellular particle made up of genetic material and protein that can invade living cells. Sub microscopic entity consisting of a single nucleic acid surrounded by a protein coat and capable of replication only within the living cells of bacteria, animals or plants. Discovery  The scientific study of viruses and the infections they cause – began in the closing years of the 19th century. Although  Louis   Pasteur  and  Edward Jenner  developed the first vaccines to protect against viral infections, they did not know that viruses existed. The first evidence of the existence of viruses came from experiments with filters that had pores small enough to retain bacteria. In 1892,  Dmitry Ivanovsky  used one of these filters to show that sap from a diseased tobacco plant remained infectious to healthy tobacco plants despite having been filtered.   Martinus Beijerinck  called the filter...