L13 Virus Replication Flashcards
(33 cards)
What are the six steps of virus multiplication?
Attatchment
Penetration
Uncoating
Biosynthesis
Assembly
Release
What does the entry to a host cell depend on?
The interaction between viral surface proteins and host cell surface proteins
= VIRUS RECEPTOR
What processes occur in the biosynthesis step of virus multiplication?
Genome replication
mRNA synthesis
Translation
What do viruses require for biosynthesis?
Host ribosomes, enzymes and precursors
Attachment slide listen
Specific binding of a virus-attatchment protein to a cellular receptor molecule on the host cell surface
How are you DNA virus genomes replicated and transcribed?
By host polymerases
Replicated by host DNA polymerases
Transcribed by host RNA polymerases
Why can’t RNA virus genomes use host polymerases to replicate and transcribe? What do they do instead?
Because host polymerases can only use DNA as a template
Therefore RNA viruses must encode their own polymerases which can use RNA as a template
What is the function of the proteins encoded by the virus genome?
- replication of the genome
- package the genome into virus particles
- alter the metabolism of the infected cell
What is the different between structural virus proteins and non-structural virus proteins?
Structural - form part of the virus
Non-structural - not incorporated into the virus particle
Why must viruses compete for host cell ribosomes?
Because viruses don’t carry their own ribsomes
What is the translation of most viral mRNAs dependant on?
The 5’ terminal cap
What do eukaryotic initiation factors bind to?
Bind to the cap and 40S ribosomal subunit
Outline post translational modification in viruses
- viral proteins undergo the same range of post translational mods as the host cell proteins e.g. acylation
- some virus genomes are translated to produce a single large viral poly protein which must be post-translation ally cleaved to release individual viral proteins
How do most enveloped viruses acquire the envelope?
By budding through the plasma membrane
- may also bud from the nucleus e.g. herpes
Outline the process of acquiring membrane and surface glycoproteins by enveloped viruses
- synthesis and co-translational membrane insertion of viral glycoproteins
- glycosylation starts in the RER
- there are vesicles which contain viral glycoproteins
- glycosylation continues in the Golgi apparatus
- viral glycoproteins are transported to plasma membrane in vesicle
- host glycoproteins in plasma membrane become part of the envelope
- nucleocapsid forms and it migrates to virus-modified membrane
- budding starts and a budding virion is formed
- results in a free infectious virus
How can the virus be released?
- by cell lysis
- by budding from plasma membrane or into lumen of ER
- spread from cell to cell via pored or by inducing fusion of their membranes
- released preceded by or followed by a maturation step
Summarise primary site replication
1) virus binds to cell-surface receptor and enters celll by fusion from without or receptor mediated endocytosis
2) viral genome must be replicated and transcribed into mRNA
3) viral proteins are translated and modified using host cell machinery
4) virions are released from cell by budding, cell lysis or cell to cell spread
How can viruses shed?
Directly from the site of primary replication
OR
Spread through the body to cause a systemic infection
What are bacteriophages?
Viruses which infect bacteria
Describe a M13 filamentous bacteriophage
- circular ssDNA
- cloning and DNA sequencing
- released without losing host cell
- budding makes own channel
What makes up a tailed phage structure?
Head - includes DNA
Collar
Tail
Long tail fibres
Base plate
Lysozyme complex
Protein needles
Why are bacteriophage important?
- can turn bacteria virulent
- alternative to antibiotics : phage therapy
- great tool in the lab for recombinant DNA technology
Which plasma protein does HIV hijack?
CCR5 which has a function of being a chemokine receptor
Which plasma protein is hijacked by rhinovirus?
ICAM-1 which has the function of Intracellular adhesion molecule
