Quiz 4: Set I

Question 1

Togavirus

Answer 1

+ssRNA
enveloped; icosahedral nucleocapsid
arboviruses (except rubella)

Multiplication strategy: intrinsic incubation period in human→extrinsic incubation period. Can have phenotypic mixing.
Examples: Rubella, EEEV

Question 2

Retrovirus

Answer 2

2 identical +ssRNA strands
enveloped; uncertain nucleocapsid.

Multiplication strategy: essential genes (gag, pol, env) encoded for. 1) extracellular phase: fusion of envelope, NC→cytoplasm. 2) intracellular phase: RT creates dsDNA with LTRs→dsDNA releases from NC and enters nucleus, integrating into cellular DNA randomly via integrase protein⟹provirus when integrated. Host RNA polymerase transcribes and replicates provirus. Viral RNA gets translated into viral proteins, and later gets packaged into NCs as full length RNA genome. New virions=NCs bud through PM.

Examples: AIDS (lentiviruses), tumor viruses (oncoviruses, incl. HTLV-1 & 2)

Question 3

Parvovirus

Answer 3

linear ssDNA
unenveloped icosahedral NC smallest human virus

Multiplication strategy: enters non-quiescent cell during S phase, ssDNA→ds template via nuclear host machinery. Transcribed and translated by host machinery; non-tumorigenic b/c can’t induce transformation.

Examples: parvovirus B-19

Question 4

Papovavirus

Answer 4

circular dsDNA; small
unenveloped, icosahedral

Multiplication strategy: early genes encode T antigen (inactivates Rb and p53 tumor suppressors)→DNA replication begins. Late genes encode capsid proteins. Big reliance on host proteins because encodes <10 genes.

Examples: papillomavirus (HPV), (polyomavirus, SV40-nonhuman)

Question 5

Adenovirus

Answer 5

single circular dsDNA
unenveloped, icosahedral

Multiplication strategy: viruses assemble in nucleus, have early mRNA (replication proteins) and late mRNA (structural, virions). E1A and E1B proteins essential for transformation.

Examples: not associated w/ tumors in humans; adenoviruses.

Question 6

Herpesvirus

Answer 6

linear dsDNA
enveloped, icosahedral

Multiplication strategy: adsorption→fusion, NC to nucleus, DNA becomes circular. mRNA, viral proteins and DNA are synthesized. New NCs assembled @nucleus, bud through nuclear membrane to become virions. Insert viral GPs in nuclear and PMs→can lead to cell fusion.

Examples: HSV1, 2, VZV, cytomegalovirus, EBV, HSV6, 7, 8

Question 7

Paramyxovirus

Answer 7

1 -ssRNA
enveloped, helical

Multiplication strategy: replicate RNA in cytoplasm; RNA-dependent RNA pol makes +RNA strand. Hemagglutinate.

Examples: mumps, measles