Plate 36

1. Plate 36 Retroviruses

2. 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

3. 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

4. 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

5. 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

6. 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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9. 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

10. 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