Quiz 1 - Weller - Intro To Virology Flashcards
What is a virus?
Submicroscopic infective agents usually regarded as non living and typically contain a protein coat around RNA or DNA core of genetic material.
They are capable of growth and multiplication only in living cells
Pepper mild mottle virus is used in what?
Contamination testing
How many virus particles in a drop of sea water?
~10 Million
The majority of viruses are what?
Bacteriophage
Majority of viruses have a _________ effect.
Limited
*Most people have been exposed to Herpes viruses
__% of the human genome is made up of endogenous retro viral sequence.
8%
What is a viral capsid?
Outer protein sheath
What are the three types of capsids?
Helical - Cylindrical
Icosahedral - 20-sided
Complex - Mix of both helical and icosahedral
What are the 3 basic function of the capsid?
Protect the genetic material
Aid entry into the cell (Attachment/penetration)
Package viral enzymes
What is the viral envelope?
Lipid membrane surrounding the nucleocapsid enriched with viral proteins (spikes/envelope proteins)
What is the tegument of the viral envelope?
Matrix protein that attaches the envelope to the capsid and is involved w/ delivering viral genetic material/replication enzymes into cells
What do membrane-bound viral proteins do?
Attach to cellular receptors, membrane fusion, and cellular entry
How are viral genomes organized?
Baltimore classification (Groups I - VII)
When is a strand (+)?
When the mRNA contained sequence can be directly used in protein synthesis
RNA and DNA (-) are complements of the _____ strand.
(+)
The Baltimore Classification has how many genome types?
Seven
Name the seven groups of viral genome types.
Group I - DS DNA (+/-)
Group II - SS DNA (+) - Goes to DS DNA (+/-)
Group III - DS RNA (+/-)
Group IV - SS RNA (+) - Goes to SS RNA (-)
Group V - SS RNA (-)
Group VI - SS RNA (+) - Uses reverse transcription to go to DS DNA
Group VII - DS DNA (+/-) - Goes to SS RNA, then uses reverse transcription, and then goes to DS DNA
*mRNA is the ultimate end point of all groups and then proteins are made
Viral genome structure consists of 4 things. Name them.
Linear
Circular
Segmented
Gapped
What does retrovirus mean?
RNA to DNA and DNA to RNA
What is the viral life cycle?
Attachment and Entry
Penetration
Uncoating
Biosynthesis
Assembly
Release
Viral life cycle: Attachment - Explain it
Binding of the virus to a cell surface protein via glycoproteins
Viral life cycle: Penetration - Explain it
Once inside host cell, it is undetected by the immune system. This is the ECLIPSE PHASE.
If antibodies are going to interfere with a virus, at what life cycle step is the most effective in preventing an infection?
Attachment and entry
What happens during the eclipse period?
Synthesis of viral components followed by assembly of new virion
What happens in the lytic cycle?
Burst the host cell and release the virions
Enveloped penetration follow 1 of 2 pathways to get in the cell. Name and give examples of each.
Fusion - HIV-1, herpesviruses, paramyxoviruses
Viropexis - Influenza, rubella, rabies
Describe fusion of enveloped penetration.
Viral attachment protein-mediated fusion of the viral envelope and plasma membrane, and capsid enters the cell directly.
*Envelope stays at the plasma membrane, while the capsid and genetic material (nucleocapsid) enter the cytoplasm.
Describe viropexis of enveloped penetration.
Receptor mediated endocytosis. Whole capsid brought into cell (endosome). Once in endosome, pH drops, and envelope fuses with endosome membrane and nucleocapsid enters cytoplasm
DOES NOT FUSE DIRECTLY WITH PLAMSA MEMBRANE, BUT FUSES WITH ENDOSOMAL VESICLE
There is a variation of viropexis. Explain it.
Clathrin-mediated endocytosis. Virus enters the cell like viropexis, but does not have an envelope to fuse with the endosomal vesicle, so it disrupts it. The drop in pH activates viral proteins and lysis of the vesicle occurs
Define susceptibility (viral infections)
Whether or not a cell expresses the receptors needed for a virus to gain entry into a cell (attachment/entry)
Define permissivity (viral infections)
If a cell contains the intracellular components that will support replication of the virus (pathways/replication)
Define resistant (viral infection)
Cell may not possess receptor or pathways used for viral replication
Cells must become __________ and ___________ to become infected by a virus.
Susceptible
Permissive
_________ DNA viruses use the host transcription processes to produce mRNA, and replicate their genetic material. ____________ DNA viruses encode most of their own replication proteins.
Smaller
Larger
Viral DNA can be directly replicated and transcribed/translated all in one go for what groups? And how?
Group I - Direct production of mRNA and synthesis of viral genomes
Group II - Synthesize DNA genome to render dsDNA, production of viral genomes, and mRNA
The concatemer is cleaved into what prior to assembly?
ssDNA viral genomic
Replication of DNA viruses can take place in what two places?
Nucleus
Cytoplasm
If replication occurs in the cytoplasm, then all replication machinery would need to be provided by the __________.
Virus
What is complex expression?
Viruses producing proteins in batches and expressing their genome in phases induced by the preceding protein products
What is the latent phase of a virus?
Dormancy where it is replicated along with all the other DNA as the cell divides
What is the lytic phase?
When the virus is in active replication
T/F - The RNA (+) virus genomes contain genetic material that can be directly transcribed.
TRUE
Tell me more about RNA (+) viruses.
- They require an RNA (-) genome for replication and the (-) acts as a template
- RNA (+) enters a cytoplasmic ribosome and make viral proteins directly
- No need to enter the nucleus, so they reproduce and assemble in the cytoplasm
- They make replication enzymes which make complementary RNA (-) templates so that more RNA (+) can be produced
T/F - RNA (-) viruses need to make a complementary RNA (+) that can be ready by host ribosomes.
TRUE
RNA (-) viruses need to make a complementary RNA (+) strand to be read by host ribosomes. So, what does it do to make that happen?
It packs it’s own RNA reverse polymerase enzymes and relies on host enzymes.
Tell me more about RNA (-) viruses.
- Can replicate in nucleus or cytoplasm
- Complementary RNA (+) strands are produced and sent to cytoplasm to be translated or retained as a template to make more RNA (-)
- Viral structural proteins made by viral RNA (+) assemble with RNA (-) strands and produce new progenitor viruses
What are retroviruses?
RNA viruses that reproduce thru a DNA intermediate
What enzymes are capable of forming DNA from RNA templates?
Reverse transcriptase
How does the reverse transcriptase work?
Reads the viral RNA, makes an RNA-DNA hybrid, DNA to nucleus where a provirus is made, then RNA is exported out of the nucleus
What happens after reverse transcription takes place?
The viral DNA may be integrated into the host genome by the activity of viral integrase enzymes and is replicated w/ everything else during cell cycling. The virus would now be in the provirus stage.
*The viral mRNA can be made from the incorporated DNA, and then viral proteins can be made
What is viral assembly?
The insertion of individual viral genomes into individual capsids. Sometimes called encapsidation.
T/F - The protein capsid is assembled in such a way as to favor the incorporation of viral genomes.
TRUE
What is the viral packaging site?
Viral genomes are spliced/modified prior to cytoplasmic assembly to prep them to enter the capsids. There is usually a specific site on the viral genome that codes for proteins intended to initiate assembly
What do non-enveloped viruses, once assembled in the cell, do to the cell?
LYSE the cell via various viral enzymes
Most typically many naked/capsid human viruses will do what to the cell?
Will trigger APOPTOSIS thru disruption of protein synthesis and/or normal cell cycle functioning.
How do enveloped viruses get out of the cell?
Tend to acquire a bit of host membrane once assembled in their capsids, and proceed down the normal protein secretion pathways
Herpesvirus takes what membrane?
Poxvirus take what membrane?
Most of the others take what membrane?
Nuclear
Organelle
Plasma
Once membrane is acquired, how are they expelled from the cell?
Exocytosis
MORE COMMONLY: BUDDING.
*The virus is now visible again to the immune system.
What are 3 things that affect mutation rate?
Genome size
Replication rate
Host conditions
What is the overall life cycle of a virus?
Infect, replicate, repeat
