Mechanisms of Viral Replication Flashcards
(36 cards)
6 Discrete Steps of Virus Replication
- Adsorption to the host cell
- Penetration or entry
- Uncoating
- Synthetic phase: transcription, translation, genome replication
- Virus Assembly
- Virus Release
Adsorption to the Host Cell
•Specific binding of the virions spikes to the host cell receptors
Two Mechanisms of Virus Entry
- Fusion
- Viropexis
Viral Entry - Fusion
- Some enveloped viruses enter cells by membrane-envelope fusion
- Viral envelope becomes part of plasma membrane
- Herpesviruses, Paramyxoviruses
Viral Entry - Viropexis
- Some enveloped viruses and naked capsid viruses are taken in by receptor mediated endocytosis
- Orthomyxoviruses, Poliovirus
Uncoating
- Removal of viral proteins
- Results in release of viral genome into cytoplasm or nucleus
- Uncoating may be complete or partial
Synthetic or Virion Components Production
- Transcription: Synthesis of mRNA
- Replication: Synthesis of viral genomes
- Early Functions: Synthesis of early proteins
- Late Functions: Replication of viral genomes and structural proteins synthesis
DNA virus replication
•Transcription
ss DNA——> ds DNA———> mRNA
•Replication
ds DNA——> ds DNA
+RNA virus replication
- RNA (+) sense viruses replicate in the cytoplasm, using their own newly synthesized RNA dependent RNA polymerase, also called RNA transcriptase (exception -retroviruses: they replicate in the nucleus via DNA intermediates)
- to synthesize the early proteins (RdRp) needed to make make more +RNA (which leads to more and more proteins being made):
(+) RNA = mRNA —-> proteins
•then, Transcription
(+) RNA——> (-) RNA——> mRNA (+) —> even more proteins
•Replication
RNA——> (-) RNA——> RNA
-RNA virus replication
- RNA (-) sense viruses replicate in the cytoplasm, using their own virion associated RNA dependent RNA polymerase (exception-orthomyxoviruses: they replicate in the nucleus)
- Transcription
(-) RNA——> (+) = mRNA
•Replication
(-) RNA——> (+) RNA——> (-) RNA
DNA Virus Transcription
RNA Virus Transcription - 3 Ways
- segmented genome
- monocistronic mRNAs
- monocistronic mRNAs translated into a polyprotein and cleaved into mature proteins
Monocistronic mRNA - Segmented RNA
Monocistronic RNA - Negative Sense RNA Viruses
Monocistronic mRNA - Positive Sense RNA Viruses
Virus Assembly - Naked Capsid Viruses
- Capsomeres assembled
- Capsomeres formed into capsids
- Nucleic acid added to form complete particles
Virus Assembly - Enveloped Viruses
- Membrane acquires viral encoded spikes or peplomers
- Matrix protein aggregates at membranes
- Nucleocapsid migrates beneath matrix protein
- Nucleocapsid enclosed by membrane (budding)
Virus Release
Productive or lytic response:
Successful viral replication cycle is called productive or lytic response.
Lytic or virulent viruses:
Viruses that can lead into productive infection are called lytic or virulent viruses.
Non-productive response:
The genome of some viruses can persist indefinitely and the host cells survives and divides without any virus production, called non-productive response.
