5: Multiplication Flashcards
Multiplication cycle of viruses?
short
- Adsorption
- Penetration
- Decapsidation
- Eclipse
- Maturation
- Release
What happens during adsorption?
attachement to the host cell
What happens during penetration?
entry into the host cell
What happens during decapsidation?
nucleic acid release
What happens during eclipse?
- expression and copy of the viral genetic information
- transcription, translation and NA replication
- different strategies according to the type of NA – > the Baltimore-system
What happens during maturation?
- assembly of progeny virions
- Polipeptide –> protein
- Glycosylation, dimer formation, antigen development at the ER, Golgi
What happens during release?
evacuation from the host cell
What are the different types of receptors in Adsorption?
- cell surface receptor
- virus surface antireceptor
What is characteristic for the Cell surface receptor of Adsorption?
- 10^4-5/cell (stable)
- usually already expressed in the embryo
- necessary for cellular functions
(ie. CD4 - HIV, acetylcholine receptor - rabies virus)
What is characteristic for the Virus surface antireceptor of Adsorption?
- more variable
- viruses adapt the cellular surface receptors dring their evolution
- related viruses usually target the same cell surface receptor
- sometimes non-related viruses have the same receptor
(ie. CAR = Coxackie-adeno receptor)
how is the stability of Virus surface antireceptor determined?
determined by the tissue or species receptor protein
What happens if the Virus surface antireceptor is negatively charged?
- repulsion
- collision by chance
What happens if the Virus surface antireceptor has reversible connection?
Cations neutralize the electrostatic power
What happens if the Virus surface antireceptor has irreversible connection?
Chemical bonds between the proteins
Penetration can be?
- energy dependent
- energy consuming
What are the 2 forms of Penetration?
- General
- Alternative
What are the General forms of penetration?
- Translocation
- endocytosis
- membrane fusion
What are the Alternative forms of penetration?
- injection
- sexfimbria
- passive
What is translocation?
penetration form
- ie picornavirus
- “trapdoor” mechanism, amorphous RNA-protein complex
What is endocytosis?
penetration form
- mostly non-enveloped viruses + herpes, pox.
- cell nutrition endosome –> phagolysosome –> decapsidation
What is membrane fusion?
penetration form
- only enveloped viruses
- viral fusion (F) protein induces
- the viral envelope merges into the cytoplasmic membrane of the host cell –> only the nucleocapsid gets into the cytosol
What is injection?
penetration form
- tailed bacteriophage
- lysozyme enzyme + contractile proteins
What is sexfimbria?
penetration form
- ribophages
- lack of cellular wall –> “bacterial sexual disease”
What is passive?
penetration form
- plant viruses
- cellular wall injuries, arthropod bites
Describe decapsidation
- uncoating
- release of the NA from the capsid
- dangerous for the virus, but necessary for the transcription
What are the strategies of Decapsidation?
- use of cellular proteases (in lysosomes)
- viral uncoating proteins (ie. poxviruses)
- partial decapsidation
- simulatneous penetration and decapsidation
What is Partial decapsidation?
- hiding the NA until the early virus protein production
- ie. DNA viruses in the nucleus, Reo-, orthomyxo-, paramyxoviruses.
How does simultaneous penetration and decapsidation happen?
by translocation and/or injection
Where does Virus assembly occur?
Usually at the site of replication –> protection
- RNA viruses + Pox, Asfarviridae –> cytoplasm
- other DNA viruses –> nucleus
Methods of virus assembly:
- the nucleic acid enters into the capsid –> Icosahedral
- The capsomers surround the nucleic acid –> helical
What helps regulate the virus assembly?
Scaffolding proteins
- envelope and matrix proteins are acquired from cellular membranes.
Types of Virus release
Passive/active way
Virus release in Non-enveloped viruses:
- -> cytolysis
- Rapid (picornav.)
- Slow (Parvov.)
- Apoptosis (adenoviridae)
Virus release in Enveloped viruses:
Budding
- Rapid (togav., paramyxov., rhabdov.)
- Slow (arenav., retrov.)
Budding sites of enveloped virus release:
Budding site is virus-specific.
- Herpesv: nuclear membrane
- Flaviv: ER
- Coronav., Bunyav: Golgi
- Asfarv., Togav., Orthomyxov., Paramyxov., Rhabdov: Cytoplasmic membrane
Virus release in Cell-associated viruses (Gammaherpesvirinae):
release at cell death or injuries
Virus release in Cell fusion (syncytium formation):
- -> membrane tunnels
- safe way of spreading (herpesv., paramyxov.)
Alternative forms of virus release:
- lysosome disintegrations (herpesviridae)
- T bacteriophages: lysyme enzyme digests the cellular wall
- plant cells are firmly connected to each other:
- -> virus spread from cell to cell
- -> mosaic pattern
