Lecture 3 Flashcards
When was it established that the viral genome is the genetic code?
In the 1950s
What was the result of the Hershey-Chase experiment?
Established that the inside of a virus (the genome) specifies the production of a virus.
What was the specific virus used in the Hershey-Chase experiment?
A bacteriophage
In the Hershey-Chase experiment, what did p32 tag?
Tagged the genome of the bacteriophage
In the Hershey-Chase experiment, what did S35 tag?
The capsule of the virus.
What question did the Hershey-Chase experiment answer?
“What initiates the viral infectious cycle?”
What type of host cell does a bacteriophage infect?
E. coli
How did the Hershey-Chase experiment work? What were the results?
The labelled bacteriophages were enabled to infect the E.coli host cell. Once the cell was infected, the viral capsules would be empty of the viral genome, and could be separated. Blending mixed the components together. Then, they were separated based on size using centrifugation. The infected bacteriophages would come out in a pellet. The empty viral capsules remained in the supernatant. The results were that s35 remained in the supernatant (capsule), and p32 was extracted in the pellet (genome).
Therefore the genome causes the viral infectious cycle/central dogma.
What is a modern day Hershey-Chase experiment?
Bacteriophages are mixed with cyanine dye. This cyanine dye binds viral genomes. Upon infection into bacterial host, the genome exits the bacteriophage, and enters the host.
What is depicted by this photo?
A modern day Hershey-Chase experiment.
What does this graph represent?
The amount of dye (genome) in the viral capsule
What does this represent?
The amount of dye (genome) in the host E. coli cell.
What did Baltimore win a Nobel prize for?
The discovery of reverse transcriptase in viruses
What is the key concept of the Baltimore viral classification system?
The viral genome must make mRNA to be read by host ribosomes, and translated into protein. The mRNA is read in the 5’-3’ direction.
Do viruses obey the central dogma?
No. They do not always obey dsDNA → mRNA → protein.
Out of the seven Baltimore classifications, what is the common goal/product of the viral genome?
mRNA, to be read by host cell ribosomes
What are the two types of DNA viruses?
dsDNA (+/-), and ssDNA (+)
What are the three types of RNA viruses?
dsRNA (+/-), ssRNA (+), ssRNA (-)
What are the two types of reverse transcriptase viruses?
ssRNA (+), dsDNA (+/-)
Is mRNA + or - if it is prepared to be translated?
+
Is the DNA of equivalent polarity to mRNA + or -?
+
Are the complements of mRNA and DNA positive or negative?
-
Which type of viral genome most closely resembles the central dogma of molecular biology?
dsDNA, (also mRNA (+) minus the dsDNA → mRNA step)
Out of viruses with RNA and DNA genomes, which evolved first
RNA viruses. DNA viruses are more complicated.
How is dsDNA converted to mRNA?
Transcribed to mRNA by DNA-dependent RNA polymerase.
In small dsDNA (<5 kbps) viruses, where does the DNA-dependent RNA polymerase come from?
From the host, the virus is to small to produce its own polymerase.
What is an example of a dsDNA virus with a genome (<5 kbps)?
Polyomaviridae, JC virus (John Cunningham). Approximately 80% of N. Americans are infected, but symptoms only show in immunocompromised individuals (ex. those with AIDS) causing degenerative brain diseases.
In larger dsDNA (36 kbps) viruses, where does the DNA-dependent RNA polymerase come from?
Still comes from the host, still not large enough to encode it
What is an example of a dsDNA virus with a genome of 36 kbps?
Adenoviridae adenovirus (multiple subtypess). Causes respiratory and GI infections in humans.
In a dsDNA virus with a large genome (100-370 kbps), where does the DNA-dependent RNA polymerase come from?
Encoded by the viral genome, as the genome is larger.
What is an example of a dsDNA virus with a genome between the size of 100-370 kbps?
Poxviridae variola virus, which causes the Smallpox disease.
In a dsDNA virus with a genome 100-370 kbps in length, RNA polymerase is encoded in the viral genome. What are the two options for where it is found?
- Already pre-made and packaged in the virion. Virus transcribes dsDNA into mRNA in the cytoplasm.
- Virus has not yet produced RNA polymerase and it is not packaged in the genome. The virus enters the nucleus, and uses host RNA polymerase to transcribe the viral RNA polymerase. For the rest of the viral life cycle the polymerase in enoded for by the virus.
