Micro Viruses

Question 1

picornavirus diseases

Answer 1

• Rhinovirus
• Hep A
• GI disease (Coxsackie)
• Heart Disease
• foot and mouth disease
• severe respiratory infection
• poliomyelitis

Question 2

picornavirus structures

Answer 2

• very small
• 1 protein repeats for capsid
• NON enveloped
• ss (+) RNA
• 5’ VpG cap
• polyprotein

Question 3

picornavirus entry

Answer 3

-RME

Question 4

picornavirus translation

Answer 4

• by host machinery
• VpG cap
• translation initiates at IRES

poly protein –> protease, capsid, replicase

Question 5

picornavirus genome replication

Answer 5

• 3D RNAP from virus
• needs VpG-UU primer
• makes (-) sense antigenome
• makes (+) sense genome
• more efficient to make (+) than (-) RNA

Question 6

assembly/release of picornavirus

Answer 6

• assembly in cytoplasm
• (+) RNA encapsulated
• unclear release – leaves cell destroyed, LYSIS OF HOST CELL

Question 7

myxovirus structure

Answer 7

• segmented (-) RNA
• no cap/tail –> seen as foreign if no NP association
• enveloped
• surface proteins: hemagluttinin (HA), neuraminidase (NA)
• cylindrical (variable in size)

Question 8

myxovirus entry

Answer 8

• HA and sialic acid interact to attach

- RME

Question 9

myxovirus transcription/genome replication

Answer 9

• viral proteins steal 5’m7G cap from host mRNA –> used as primers to make (+) viral mRNA.
• exported from nucleus
• transcribed back into (-) RNA to replicate genome
• associates with NP so it isn’t “foreign”

Question 10

myxovirus assembly/release

Answer 10

• assembly at plasma membrane
• buds off
• neuraminidase cleaves receptor on host cell to prevent reattachment

Question 11

tamiflu/oseltamivir

Answer 11

• inhibits neuraminidase
• budded virions stay bound to same cell (not released)
• competes with sialic acid

Question 12

myxovirus reassortment/mutation

Answer 12

• antigenic shift: two viruses infect, genomes shuffle
• antigenic drift: mutations arise randomly

Both occur at same time, constantly –> high diversity

Question 13

papilloma virus structure

Answer 13

• non enveloped
• 2 protein capsid (L1, L2 –> req for penetration)
• dsDNA (circular, histones)

Question 14

papilloma entry into cells

Answer 14

• attach to HSPG on basement membrane (exposed at sites of trauma)
• infection starts in basal layer
• RME

Question 15

papilloma early gene expression

Answer 15

• E1
• E2: master regulator
• E6: binds p53, prevents apoptosis
• E7: binds Rb, triggers cell division

Question 16

papillomavirus genome replication

Answer 16

• NOT integrated into host genome
• E1, E2 recruit host machinery
• replicated once per cell cycle (natural amount)
• in differentiated epithelial cells: E6, E7 activate DNA synthesis of ONLY viral genome

Question 17

papilloma late gene expression

Answer 17

• ONLY in terminally differentiated keratinocytes
• DNA replication
• differential splicing for L1, L2 capsid proteins

Question 18

papillomavirus assembly/release

Answer 18

• L1, L2 transported to nucleus
• DNA packaged into capsid
• virions released during natural life cycle of cell (differentiate, die, slough off)
• no need to lyse cell

Question 19

HPV16,18 transformation in cervical epithelium (oncogenesis)

Answer 19

• RARE
• integrates part of genome into host
• selection for cells with E6, E7, but NOT E2 (unregulated, triggers cell division, prevents apoptosis)
• no virion production (rest of viral genome lost or deleted

Question 20

retrovirus structure

Answer 20

• enveloped
• ss(+) RNA
• Gag: capsid proteins
• Pol: protease (PR), reverse transcriptase (RT), integrase (IN)
• Env: envelope glycoprotein

Question 21

retrovirus entry

Answer 21

• fusion of viral and cellular membranes
• *NOT via RME
• reverse transcription occurs immediately

Question 22

retrovirus genome replication

Answer 22

• reverse transcription catalyzed by viral RT
• host tRNA primes
• RT synthesizes wrong direction first
• uses segment to synthesize correct direction
• makes (-) DNA
• makes dsDNA
• LTR regions become identical, form LTR circle
• new ds DNA imported into nucleus, integrated into host genome by viral integrase
• into random location

Question 23

retrovirus assembly/release

Answer 23

• viral proteins targeted to plasma membrane
• proteins assemble in a curvature
• bud off
• cell survives
• not infectious until MATURATION (viral protease cleaves Gag, Pro)

Question 24

retroviral oncogenesis

Answer 24

1) viral inserts upstream of a proto-oncogene

2) viral genome already contains an oncogene

Question 25

All capsids are icosahedral except...

Answer 25

Myxovirus --> helical nucleocapsid

Question 26

Retrovirus examples

Answer 26

Rous sarcoma virus, HIV, FeLV