Plate 36 Retroviruses

Reverse transcriptase Retrovirus Structure All retroviruses: Are surrounded by a viral envelope Are icosahedral in shape Contain 2 identical molecules of RNA Contain the enzyme reverse transcriptase Viral RNA Reverse transcriptase Glycoproteins Lipids Envelope

DNA Viruses vs. Retroviruses “Retro” means “backwards” DNA viruses undergo transcription and translation: DNA  RNA  viral proteins Retroviruses undergo reverse transcription and translation: RNA  DNA  RNA  viral proteins Reverse transcriptase allows the single-stranded RNA to be transcribed into double-stranded DNA

Infection Glycoproteins on the viral envelope allow the virus to attach to the receptor sites of the host cell The virus then fuses with the cell membrane of the host

Reverse Transcription Once a virus has penetrated the cell membrane, the RNA undergoes reverse transcription in the cytoplasm: RNA  DNA The viral DNA then gets integrated into the host cell’s chromosomal DNA (viral DNA now known as a provirus) The viral DNA is then passively replicated

Latency Retroviral DNA can remain dormant in the host cell’s chromosomal DNA for a long period of time (latency – from Latin word for “hidden”) This is part of the lysogenic cycle

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Retrovirus Diseases Retrovirus infections can lead to HIV/AIDS, cancer, and tumors Reverse-transcriptase inhibitors prevent viruses from converting their RNA into DNA, thus rendering them inactive HIV virus

Fun Facts! It is believed that almost 8% of human DNA comes from retroviruses, most of which is considered “junk DNA” During reverse transcription, mutations are common . . . which allows retroviruses to become resistant to antiviral drugs Viral DNA may trigger cancer and tumor growth by being randomly integrated into a oncogene