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