Ch 4: Viruses

Question 1

+ sense aka

Answer 1

+ sense = coding strand = mRNA
- + sense RNA = +RNA, can be used itself as mRNA (bc the coding strand = mRNA
- after the RNA polymerase is made, -RNA is made which also serves as a template to make more +RNA
+RNA retroviruses: mRNA is transcribed from the sDNA intermediate

Question 2

• sense aka

Answer 2

• sense = template strand
• (-)DNA strand of genome serves as template to make mRNA
• (-)RNA viruses the -RNA serves as the template for transcribing more +mRNA (brings its own RNA polymerase with it)

Question 3

all naked capsid viruses have what structure

Answer 3

• all naked capsid viruses are icosahedral

- naked viruses have a protein coat

Question 4

all helical viruses are

Answer 4

• enveloped, there are no naked helical viruses
• enveloped viruses are covered in host membrane w/ virus specified glycoproteins (critical for infectiousness of viral progeny)
• enveloped viruses are inactivated by heat/detergents/acids, etc bc the lipid envelope holds the glycoproteins essential for attachment. Dissolving the envelope inhibits attachment and therefore uptake.

Question 5

DNA viruses (encapsulated) in order from largest to smallest

Answer 5

1. poxvirus
2. herpesvirus
3. hepadna

Question 6

naked DNA viruses in order from largest to smallest

Answer 6

1. adenovirus
2. polyoma, papilloma
3. parvovirus

Question 7

RNA viruses (encapsulated) in order from largest to smallest

Answer 7

1. paramyxovirus
2. rhabdovirus
3. orthomyxovirus
4. coronavirus
5. togavirus
6. flavivirus

Question 8

naked RNA viruses (in order from largest to smallest)

Answer 8

1. reovirus
2. calicivirus, hepevirus
3. picornavirus

Question 9

arthropod-borne viruses (insect vector) aka

Answer 9

arboviruses

Question 10

HIV receptors on host cell

Answer 10

• CD4
• CCR5 (macrophage)
• CXCR4 (Th cells)
• target cells: Th cells, macrophages, microglia

Question 11

receptor for rabies virus

Answer 11

Ach receptor

Question 12

release of naked viruses

Answer 12

• naked viruses lyse the host cells

- thus there are no persistent productive infections w/ naked viruses (only cytolytic productive or latent infections)

Question 13

release of enveloped viruses

Answer 13

• budding leads to cell senescence (aging) but cells may produce a low level of virus for years (HepB)
• the glycoproteins on the enveloped viral surface = essential for viral infectivity

Question 14

interferon

Answer 14

• made by infected cells for uninfected cells
• production of IFN (and most immunologic cytokines) is under control of transcription factor NFκB
• inhibits viral protein synthesis by:
  1. through activation of an RNA endonuclease, which digests viral RNA
  2. by activation (via phosphorylation) of protein kinase that inactivates eIF2, inhibiting viral protein synthesis
• exogenous IFN (made via recombination technology) may be used in antiviral therapy for chronic, active HBV and HCV infections
• therefore virus can’t replicate and can be killed

Question 15

Which Hep viruses are transmitted fecal/orally?

Answer 15

• “vowels in the bowels” A and E are from something you ate.
• these are both naked viruses
• Hep B, C, D are all enveloped
• HAV = “infectious Hepatitis”; Acute (A = Acute)
• HEV = “enteric hepatitis” HEV is extremely serious in pregnant patients!
• HBV “serum”; both acute and chronic (B=Both)
• HCV “post-transfusion” is chronic (C= Chronic)

Question 16

DNA viruses 3 exceptions

Answer 16

• all DS except parvovirus
• all icosahedral, except poxviruses = brick-shaped complex
• all replicate their DNA in the nucleus, except poxvirus (poxviruses have a virion-associated transcriptase (DNA dependent RNA polymerase) so it can transcribe its own NA in the cytoplasm and make all of the enzymes and factors necessary for replication of the poxvirus DNA in the cytoplasm.

Question 17

Mnemonic for DNA viruses

Answer 17

Pardon Papa As He Has Pox
Par: parvovirus
P: papillomavirus, polyomavirus
A: Adenovirus
He: Hepadnavirus
H: Herpes virus
Pox: Poxvirus