Lecture 3

Question 1

When was it established that the viral genome is the genetic code?

Answer 1

In the 1950s

Question 2

What was the result of the Hershey-Chase experiment?

Answer 2

Established that the inside of a virus (the genome) specifies the production of a virus.

Question 3

What was the specific virus used in the Hershey-Chase experiment?

Answer 3

A bacteriophage

Question 4

In the Hershey-Chase experiment, what did p32 tag?

Answer 4

Tagged the genome of the bacteriophage

Question 5

In the Hershey-Chase experiment, what did S35 tag?

Answer 5

The capsule of the virus.

Question 6

What question did the Hershey-Chase experiment answer?

Answer 6

“What initiates the viral infectious cycle?”

Question 7

What type of host cell does a bacteriophage infect?

Answer 7

E. coli

Question 8

How did the Hershey-Chase experiment work? What were the results?

Answer 8

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.

Question 9

What is a modern day Hershey-Chase experiment?

Answer 9

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.

Question 10

What is depicted by this photo?

Answer 10

A modern day Hershey-Chase experiment.

Question 11

What does this graph represent?

Answer 11

The amount of dye (genome) in the viral capsule

Question 12

What does this represent?

Answer 12

The amount of dye (genome) in the host E. coli cell.

Question 13

What did Baltimore win a Nobel prize for?

Answer 13

The discovery of reverse transcriptase in viruses

Question 14

What is the key concept of the Baltimore viral classification system?

Answer 14

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.

Question 15

Do viruses obey the central dogma?

Answer 15

No. They do not always obey dsDNA → mRNA → protein.

Question 16

Out of the seven Baltimore classifications, what is the common goal/product of the viral genome?

Answer 16

mRNA, to be read by host cell ribosomes

Question 17

What are the two types of DNA viruses?

Answer 17

dsDNA (+/-), and ssDNA (+)

Question 18

What are the three types of RNA viruses?

Answer 18

dsRNA (+/-), ssRNA (+), ssRNA (-)

Question 19

What are the two types of reverse transcriptase viruses?

Answer 19

ssRNA (+), dsDNA (+/-)

Question 20

Is mRNA + or - if it is prepared to be translated?

Answer 20

+

Question 21

Is the DNA of equivalent polarity to mRNA + or -?

Answer 21

+

Question 22

Are the complements of mRNA and DNA positive or negative?

Answer 22

-

Question 23

Which type of viral genome most closely resembles the central dogma of molecular biology?

Answer 23

dsDNA, (also mRNA (+) minus the dsDNA → mRNA step)

Question 24

Out of viruses with RNA and DNA genomes, which evolved first

Answer 24

RNA viruses. DNA viruses are more complicated.

Question 25

How is dsDNA converted to mRNA?

Answer 25

Transcribed to mRNA by DNA-dependent RNA polymerase.

Question 26

In small dsDNA (<5 kbps) viruses, where does the DNA-dependent RNA polymerase come from?

Answer 26

From the host, the virus is to small to produce its own polymerase.

Question 27

What is an example of a dsDNA virus with a genome (<5 kbps)?

Answer 27

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.

Question 28

In larger dsDNA (36 kbps) viruses, where does the DNA-dependent RNA polymerase come from?

Answer 28

Still comes from the host, still not large enough to encode it

Question 29

What is an example of a dsDNA virus with a genome of 36 kbps?

Answer 29

Adenoviridae adenovirus (multiple subtypess). Causes respiratory and GI infections in humans.

Question 30

In a dsDNA virus with a large genome (100-370 kbps), where does the DNA-dependent RNA polymerase come from?

Answer 30

Encoded by the viral genome, as the genome is larger.

Question 31

What is an example of a dsDNA virus with a genome between the size of 100-370 kbps?

Answer 31

Poxviridae variola virus, which causes the Smallpox disease.

Question 32

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?

Answer 32

1. Already pre-made and packaged in the virion. Virus transcribes dsDNA into mRNA in the cytoplasm.
2. 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.