plate 36
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Plate 36Retroviruses
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
Glycoproteins Lipids
Envelope
Viral RNA
Reverse transcriptase
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
• http://highered.mcgraw-hill.com/sites/0072556781/student_view0/chapter18/animation_quiz_3.html
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
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