Viral Genome

Question 1

what was the original hershey-chase blender experiment? what did it prove?

Answer 1

1. Allow bacteriophage to infect with radioactive genome DNA or to radioactive box
2. “Blend” (remove bacteriophage)
3. “Separate” (centrifugation)
4. Radioactive phosphorus could be detected in host (pellet)

genome is key

Question 2

what was the modern day hershey-chase experiment?

Answer 2

1. Bacteriophage mixed with cyanine dye (binds viral genomes)
2. Upon infection into bacterial host; dye leaves bacteriophage and enters host interior

• fluroescence decreases in phage capsid and increases in cell interior

Question 3

what was the purpose of the hershey-chase experiment

Answer 3

what causes the viral infection: the nucleic acid or the protein shell?

Question 4

What is the baltimore classification scheme of viruses?

Answer 4

classifies viruses according to their genome in 7 groups

Question 5

what is the goal (no matter which of the 7 classifications used)?

Answer 5

make a (+) ss mRNA to make proteins read in 5’-3’ direction

Question 6

what does the (+) and (-) mean for nucleic acid classification?

Answer 6

(+) ready to be read by ribosomes

Question 7

What are the 7 types of viral genomes?

Answer 7

RNA:
1. ss + RNA
2. ss - RNA
3. ds RNA
4. ss + RNA with DNA intermediate

DNA:
1. ss DNA
2. ds DNA
3. gapped DNA

Question 8

characteristic of double strand DNA genome?

Answer 8

• DNA-dependent RNA polymerase transcription turns dsDNA to ssRNA to proteins
• polymerase can be from host (small) or from virus (large) depending on viral genome size

Question 9

what is an example of a viral family + virus that belongs to dsDNA group that has RNA polymerase from host?

Answer 9

Polyomaviridae -> JC virus (good immune response unless immunocompromised)

Question 10

what is an example of a viral family + virus that belongs to dsDNA group that has RNA polymerase from virus?

Answer 10

Poxviridae -> variola virus (smallpox)

Question 11

method of gapped double stranded DNA genome to mRNA?

Answer 11

1. start with ss/ds DNA
2. use viral-associated DNA poly or reverse transcriptase to make dsDNA by filling gaps
3. host DNA-dep RNA poly makes +ssRNA

Question 12

example of gapped ds DNA genome?

Answer 12

Hepadnaviruses (Hepatitis B Viruses)

Question 13

method of ss DNA genome to mRNA?

Answer 13

1. ssDNA uses DNA poly/rev transcriptase to make ss/dsDNA
2. ss/dsDNA uses same enzymes to make dsDNA
3. dsRNA uses host DNA-dep RNA poly to make + ssRNA

Question 14

example of ss DNA genome?

Answer 14

Parvoviruses: leukemia for cat/dog intestine, hematopoietic system and fetus

Question 15

what does the virus do if it has an RNA based genome since the host does not?

Answer 15

Host does not have an enzyme that is an RNA-dep RNA poly

so (-) RNA strands need virus RNA-dependent RNA poly to make mRNA readable by host translation machinery

Question 16

method of ds RNA genome to mRNA?

Answer 16

1. dsRNA uses viral RNA-dep RNA poly with (-) RNA strand as template
2. makes + ssRNA

Question 17

example of ds RNA genome?

Answer 17

Reoviridae Rotavirus
- gastroenteritis worldwide and infant mortality

Question 18

method of ss +RNA genome to mRNA?

Answer 18

• either: ready!
  No need for a virally encoded RNA-dependent polymerase

or
1. + ssRNA uses reverse transc to make ssDNA
2. host uses DNA poly to make ss/ds DNA, then ds DNA
3. ds DNA -> +ssRNA with DNA-dep RNA poly

Question 19

example of ready ss+RNA genome?

Answer 19

Picornaviridae Poliovirus
- paralytic polyomyelitis: inflammation of motor neurons of spinal cord and brain stem
- Coronaviridae

Question 20

example of not ready ss+RNA genome?

Answer 20

Retroviridae: HIV

Question 21

ssDNA can’t be

Answer 21

transcribed

Question 22

method of ss (-)RNA genome to mRNA?

Answer 22

1. (-) ssRNA is in wrong direction
2. uses viral RNA-dep RNA poly to make (+) ssRNA

Question 23

example of ss (-)RNA genome?

Answer 23

1. Paramyxoviridae (measles)
2. Orthomyxoviridae (influenza, respiratory disease)
3. Filoviridae Ebola virus (L protein is RNA poly)