RNA Virus 1

Question 1

Name all the RNA viruses and the classes they belong to discussed in class

Answer 1

Cold and Polio (picornavirus)
Hep C and Dengue (flavivirus)
HIV (Retrovirus)
MERS (Coronavirus)
Ebola (Filovirus)
Rabies (Rhabdovirus)
Flu (Orthomyxovirus)
Croup (paramyxovirus)

Question 2

Why are RNA viruses important?

Answer 2

huge medical burden, high rate of mutation,

Question 3

Why is the high rate of mutation for RNA viruses important?

Answer 3

confers resistance to antivirals, barriers to vaccines, reassortment of genome segments, pandemics

Question 4

What are the common features of RNA Viruses?

Answer 4

RNA is the genetic material and template for protein synthesis
dual purpose of replication is to copy the genome and make mRNA
diverse strategies have evolved to accomplish these dual goals

Question 5

In the realm of RNA viruses, define transcription and replication?

Answer 5

transcription=mRNA synthesis

replication=RNA genome synthesis

Question 6

What are the 3 main genome types of RNA viruses?

Answer 6

dsRNA, (+)ssRNA, (-)ssRNA

Question 7

What is RNA- dependent RNA polymerase (RDRP)

Answer 7

a viral polymerase used to transcribe the (-)ssRNA to (+) ssRNA so that it can code for a protein

Question 8

What is the (+) strand? What is the process that ocucrs for (+) ssRNA?

Answer 8

sense strand, mRNA; if a viral genome is (+) ssRNA, then it is converted first to a (-) strand then back to a (+) strand.

Question 9

Why do viruses need RNA dependent RNA polymerase?

Answer 9

cells don’t have enzymes to transcribe RNA from RNA; to combat this all viruses encode an RNA polymerase to copy their genome and make mRNA

Question 10

Is RDRP efficient?

Answer 10

Yes, highly efficient

Question 11

Where does RDRP do its work?

Answer 11

cytoplasm

Question 12

What is the exception to the site of RDRP action?

Answer 12

influenza virus

Question 13

What are RNA, RDRP, nucleoproteins, and accessory proteins?

Answer 13

not floating free in the cytoplasm

Question 14

Where does replication occur? Why is this important?

Answer 14

cell membranes (endosomes, lysosomes, ER vesicles); concentrates all component and increases efficiency

Question 15

Describe the fidelity of RDRP.

Answer 15

Low!
high error rate
RNA virus stocks are mixtures of WT and mutant forms

Question 16

How does rapid evolution by recombination occur?

Answer 16

Exchanging large sections produces new genomes; hybrids may have new features (antigens, virulence factors).

Question 17

Does rapid evolution by recombination occur often?

Answer 17

Yes, its a high frequency event

Question 18

What are the segmented RNA viruses?

Answer 18

Reo, Retro, Bunya, Arena, and Orthomyxo, (influenza virus) etc

Question 19

Why is reassortment of genome segments important?

Answer 19

segments can mix if the cell is infected with multiple strains

new strains might be highly virulent

Question 20

What are the consequences of RNA Virus genetic diversity?

Answer 20

Mutants arise frequently
new variants may cause new diseases
drugs and vaccines lose effectiveness
viruses are not pure populations–>each are quasispecies

Question 21

Describe the characteristics of Poliovirus.

Answer 21

Picornaviridae, enterovirus

(+) ssRNA, linear mRNA molecule

Question 22

How does poliovirus infect the host? Is there a vaccine?

Answer 22

infects GI epithelial cells, may spread to muscles and neurons; yes, vaccination with live or killed virus induces protective antibodies

Question 23

How is poliovirus transmitted? Describe pathogenesis.

Answer 23

Fecal-oral: persists in water supply; infects only humans

95% asymptomatic acute GI infection
5% mild disseminated disease
1% paralytic infection of motor neurons

Question 24

What recpetor does poliovirus bind on the cell surface?

Answer 24

CD155

Question 25

Describe Poliovirus entry

Answer 25

changes shape after binding to the recpetor, capsid proteins become hydrophobic capsid proteins form pore through membrane RNA genome enters cell at plasma or endosome membrane

Question 26

Does Poliovirus make use of RDRP?

Answer 26

Yes

Question 27

What enzyme copies (+) and (-) strands?

Answer 27

the same RDRP enzyme

Question 28

What happens triggers the switch from mRNA to genome RNA synthesis?

Answer 28

When capsid proteins accumulate, new mRNA is packaged instead of translated

Question 29

What are some of the issues with (+) RNA?

Answer 29

Collisions occur between RDRP and ribosomes, but they are not a big problem

Question 30

When does translation occur, when does (-) RNA synthesis occur?

Answer 30

1st, when RDRP is scarce, later when RDRP is abundan

Question 31

What is the association of RDRPs?

Answer 31

all RNA viruses encode RDRP, retroviruses encode reverse transcriptase; (-)RNA and dsRNA viruses must package RDRP in the virion; (+) RNA viruses may or may not package the RDRP in the virion

Question 32

If RDRP is not present in the virion, then what is necessary to make RDRP before replication can occur?

Answer 32

protein synthesis

Question 33

How is poliovirus diagnosed and treated?

Answer 33

diagnosis: motor neuron involvement, serology and culture treatment: control symptoms, breathing support if needed

Question 34

How is poliovirus prevention?

Answer 34

vaccine and sanitation