viral genomes Flashcards
what was the significance of the hershey-chase blender experiment?
serves as proof that the genome is key
used to see if the nucleic acid or the protein shell specifies the production of a virus
what were the steps of the hershey-chase blender experiment?
they allowed bacteriophage to infect with radioactive precursors to DNA (phosphorus) OR protein (sulfur) – the experiments were conducted separately!
“blend”: they then separated the attached capsid from the membrane
“separate”: they then centrifuged mixture. bacteria that contains the viral genome is heavier and will thus, separate first
radioactive phosphorus is found in the bacteria but the capsid material wasn’t passed down
- phosphorus detected in cells
- sulfur detected in the supernatant
how’s the modern day hershey-chase experiment different from the original?
uses fluorescent dyes instead of radioactive elements
what are the steps of the modern day hershy-chase experiment?
will bind to the viral genomes
upon infection into bacterial host, the dye leaves the bacteriophage and enters host interior
- losing fluorescence in the virus = increasing the fluorescence in the cell
in what direction is mRNA read?
in the 5’ to 3’ direction as host machinery is used!
what are the 7 types of viral genome?
+ssRNA
-ssRNA
dsRNA
+ssRNA with DNA intermediate
ssDNA
dsDNA
gapped dsDNA
why are there multiple types of viral genome?
variety in the genome is due to evolution! RNA viruses were first; DNA viruses are younger
how is dsDNA prepared for translation?
pathway is similar to the central dogma
dsDNA -> +ssRNA via DNA-dependent RNA polymerase
- this enzyme is from the host
larger viral genomes will encode for their own DNA-dependent RNA polymerase as it increases efficiency of transformation step when infecting host cells
what is an example of a dsDNA containing virus that uses its own RNA polymerase for transcription?
variola virus of the poxviridae family
it causes a disease called smallpox, which causes “bubbles” to appear on the skin
what is an example of a dsDNA containing virus?
JC virus from the polyomaviridae
80% of North Americans are infected but the immune system takes care of the virus
however, immunocompromised patients (e.g. AIDS patients) will develop degenerative diseases due to the virus
how is gapped dsDNA (ss/dsDNA) prepared for translation?
one strand is longer than the other - it cannot undergo transcription – it also contains piece of RNA
first, fill in the gaps with a viral DNA-polymerase
then use DNA-dependent RNA polymerase from the host to transcribe the DNA into +ssRNA
what is an example of a gapped dsDNA containing virus?
hepadnaviridaes (includes hepatitis B)
hepatitis B is now treatable but can cause liver damage
it spreads thru sexual contact and is 100 times more infectious than HIV-1
how is ssDNA prepared for translation?
single strands can’t be copied to mRNA
must use host enzymes as the genome lacks variety, and doesn’t encode for their own enzymes
host DNA polymerase makes ss/dsDNA from ssDNA
host DNA-dependent RNA polymerase makes mRNA from dsDNA
what is an example of a ssDNA containing virus?
paroviruses
known for cat/dog viruses
they infect cells of intestine, hematopoietic system, and fetus
e.g. canine paroviruses infect and kill puppies
how are RNA genomes different from DNA genomes?
RNA-dependent enzymes are needed for these genomes but hosts do not have them, thus, viruses need their own virally encoded RNA-dependent RNA polymerase to make mRNA readable by host-translation machinery
