BS 161 1st Edition Lecture 36 Outline of Last Lecture I Viruses Outline of Current Lecture II Viruses continued Current Lecture lysogenic cycle replicates the phage genome without destroying the host prophage intergrated viral DNA temperate phages phages that use both the lytic and lysogenic cycles many viruses that infect humans have a membranous envelope viral glycoproteins on the envelope bind to specific receptor molecules on the surface of a host cell viral glycoproteins are synthesized in the rough endoplasmic reticulum retroviruses use reverse transcriptase to copy their RNA genome into DNA HIV is the retrovirus that causes AIDS reverse transcriptase RNA dependent DNA polymerase HIV infects immune system T cells AZT inhibitor of reverse transcriptase treatment for HIV HIV evolves and renders AZT useless fairly quickly provirus viral DNA that is integrated into the host genome remains a permanent resident of the host cell unlike a prophage the host s RNA polymerase transcribes the proviral DNA into RNA molecules the RNA molecules function both as mRNA for synthesis of viral proteins and as genomes for new virus particles released from the cell since viruses can reproduce only within cells they probably evolved as bits of cellular nucleic acid candidates for the source of viral genomes are plasmids circular DNA in bacteria and yeasts and transposons small mobile DNA segments plasmids transposons and viruses are all mobile genetic elements
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