Micro Viruses Flashcards
picornavirus diseases
- Rhinovirus
- Hep A
- GI disease (Coxsackie)
- Heart Disease
- foot and mouth disease
- severe respiratory infection
- poliomyelitis
picornavirus structures
- very small
- 1 protein repeats for capsid
- NON enveloped
- ss (+) RNA
- 5’ VpG cap
- polyprotein
picornavirus entry
-RME
picornavirus translation
- by host machinery
- VpG cap
- translation initiates at IRES
poly protein –> protease, capsid, replicase
picornavirus genome replication
- 3D RNAP from virus
- needs VpG-UU primer
- makes (-) sense antigenome
- makes (+) sense genome
- more efficient to make (+) than (-) RNA
assembly/release of picornavirus
- assembly in cytoplasm
- (+) RNA encapsulated
- unclear release – leaves cell destroyed, LYSIS OF HOST CELL
myxovirus structure
- segmented (-) RNA
- no cap/tail –> seen as foreign if no NP association
- enveloped
- surface proteins: hemagluttinin (HA), neuraminidase (NA)
- cylindrical (variable in size)
myxovirus entry
- HA and sialic acid interact to attach
- RME
myxovirus transcription/genome replication
- 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”
myxovirus assembly/release
- assembly at plasma membrane
- buds off
- neuraminidase cleaves receptor on host cell to prevent reattachment
tamiflu/oseltamivir
- inhibits neuraminidase
- budded virions stay bound to same cell (not released)
- competes with sialic acid
myxovirus reassortment/mutation
- antigenic shift: two viruses infect, genomes shuffle
- antigenic drift: mutations arise randomly
Both occur at same time, constantly –> high diversity
papilloma virus structure
- non enveloped
- 2 protein capsid (L1, L2 –> req for penetration)
- dsDNA (circular, histones)
papilloma entry into cells
- attach to HSPG on basement membrane (exposed at sites of trauma)
- infection starts in basal layer
- RME
papilloma early gene expression
- E1
- E2: master regulator
- E6: binds p53, prevents apoptosis
- E7: binds Rb, triggers cell division
papillomavirus genome replication
- 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
papilloma late gene expression
- ONLY in terminally differentiated keratinocytes
- DNA replication
- differential splicing for L1, L2 capsid proteins
papillomavirus assembly/release
- 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
HPV16,18 transformation in cervical epithelium (oncogenesis)
- 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
retrovirus structure
- enveloped
- ss(+) RNA
- Gag: capsid proteins
- Pol: protease (PR), reverse transcriptase (RT), integrase (IN)
- Env: envelope glycoprotein
retrovirus entry
- fusion of viral and cellular membranes
- *NOT via RME
- reverse transcription occurs immediately
retrovirus genome replication
- 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
retrovirus assembly/release
- viral proteins targeted to plasma membrane
- proteins assemble in a curvature
- bud off
- cell survives
- not infectious until MATURATION (viral protease cleaves Gag, Pro)
retroviral oncogenesis
1) viral inserts upstream of a proto-oncogene
2) viral genome already contains an oncogene
