Virology Flashcards
What are virons?
A complete virus particle
What are the four different types/forms of genetic material that viruses can have?
ssRNA
ssDNA
dsRNA
dsDNA
Which viral genetic material is more stable, RNA or DNA?
DNA
What is positive sense RNA?
When the RNA is in the same sense as the mRNA it produces
What must RNA viruses have in order to reproduce inside the host cell?
they must encode their own RNA pol
Do viruses have ribosomes?
No
What is the size range for viruses?
20-300 nm
What is a nucleocapsid?
When the capsid lies within the
lipid membrane of an enveloped virus, it is
referred to as the nucleocapsid
What are the three forms of capsids?
Helical
Icosahedral
Complex
What is the helical structure of a capsid composed of? (numbe of subunit types, shape, etc)
One type of subunit wrapped around the nucleic acid like a helix
What is the icosahedral capsid structure?
made up of regularly
repeating patterns of subunits. They are closed
structures consisting of 20 equilateral triangular
faces.
What are the minimal components of a virion? Maximal
Min :Capsid + nucleic acids
Max: above + matrix, envelope, attachment proteins
What is a viral envelope?
A lipid membrane that surrounds the viral particle, which is derived from the host cell
Why are enveloped viruses more delicate?
Need moist environment
What must negative sense RNA molecules do to become infectious?
Change to the positive sense
What are the three factors that are used to classify viruses?
Genome
Capsid structure
Mode of replication
The parvovirus has what type of genome?
ss DNA
The papovaviridae virus has what type of genomic makeup?
ds DNA
The adenovirus has what type of genomic makeup?
dsDNA
The Herpesviridae virus has what type of genomic makeup?
dsDNA
The poxviridae virus has what type of genomic makeup?
dsDNA
The hepadnaviridae virus has what type of genomic makeup?
dsDNA
What are the DNA viruses that infect humans? (HHAPPPy)
Herpesviridae Hepadnaviridae Adenoviridae Parvoviridae Papovaviridae Poxviridae
The reoviridae virus has what type of genomic makeup?
dsRNA
The orthomyxoviridae virus has what type of genomic makeup?
-ssRNA
The paramyxoviridae virus has what type of genomic makeup?
-ssRNA
The rhabdoviridae virus has what type of genomic makeup?
-ssRNA
The bunyaviridae virus has what type of genomic makeup?
-ssRNA
The arenviridae virus has what type of genomic makeup?
-ssRNA
The filviridae virus has what type of genomic makeup?
-ssRNA
The togaviridae virus has what type of genomic makeup?
+ssRNA
The flaviviardae virus has what type of genomic makeup?
+ssRNA
The corona viridae virus has what type of genomic makeup?
+ssRNA
The retroviridae virus has what type of genomic makeup?
+ssRNA
The picronviridae virus has what type of genomic makeup?
+ssRNA
The caliciviridae virus has what type of genomic makeup?
+ssRNA
The hepeviridae virus has what type of genomic makeup?
+ssRNA
Are naked capsule viruses stable to the environment?
Yes
How are naked iral capsules released from the cell?
Through lysis
What are the clinical consequences of naked capsid viruses?
They are able to dry out but retain their infectivity, as well as survive inhospitible conditions
True or false: capsid virsuses are able to withstand detergents?
True
What are the clinical consequences of enveloped viruses?
must stay wet, and are very labile.
How are enveloped viruses released from the cell?
With a modified cell envelope
Can enveloped viruses survive the GI tract? Can capsid viruses?
Capsids yes, enveloped no
Do capsid viruses kill the cell when released? Enveloped?
Capsids kill
Enveloped don’t
What are the six stages of replication for a virus?
- Attachment
- Entry
- mRNA production
- Protein and gene synthesis
- Viron assembly
- Egress
What is direct fusion?
How enveloped viral particles enter the cell through fusion of their membranes
What is the consequence of leaving part of the fused membrane on the cell membrane?
The cell can then fuse with another cell to form multinucleated cells
What is the other way that enveloped cells can enter a cell, besides direct fusion? What does the virus have then?
Receptor mediated endocytosis normally used for growth factor uptake, causing the whole enveloped particle to be surrounded by an additional envelope. fusion of the two envelopes releases the virus
What is the way that non-enveloped viruses enter the cell?
Through receptor mediated pathway
How do dsDNA viruses transcribe their geneome?
Use the cell RNA pol
How do ssDNA viruses transcribe their genome?
Use cell DNA repair enzymes to produce dsDNA
How do +ssRNA viruses transcribe their genome?
Use a reverse transccriptase to produce dsDNA, or use it just like a normal ssRNA
How do -ssRNA viruses transcribe their genome?
use a viral RdRp (RNA dependent RNA pol) to produce mRNA
How do dsRNA viruses transcribe their genome?
Use a viral RdRp to produce mRNA
What are the two solutions to achieving viral DNA replication when the cell is not in S-phase? (for DNA viruses)
- Make cellular DNA replication machinery available
2. Encode viral proteins to synthesize genome
Why does HPV cause CA?
Produce E6 and E7 to push cell cycle forward
What is the solution for + sense RNA viruses to replicate their genome?
Encode RdRp
What is the solution for - sense RNA viruses to replicate their genome?
Package RdRp within the viral particle
What are the six viruses that are negative sense ssRNA, and need to bring an RdRp with them?
(Always Bring Pol Or Fail Replication)
Arenaviridae bunyaviridae Paramyxoviridae Orthomyoxoviridae Filoviridae Rhabdoviridae
What are the 5 steps of viral assembly?
- Individual viral proteins form into capsid subunits
- Subunits combine to form complete capsids
- Viral genome/other viron components packaged
- virus exits cell (w/ or w/o envelope)
How are helical capsids formed?
From a signal protein on the nucleic acid structure, which causes polymerization or proteins in both directions around it
How are icosahedral capsid viruses formed?
Form the capsule, then thread in nucleic acids
What is the process of budding?
When glycoproteins are attached to the outer layer of the plasma membrane, then attract matrix proteins and viral nucleic acids
What are virulence genes?
Genes that aid in the disease causing process
What is viremia?
Viruses in the blood (like bacteremia)
What is tropism?
When a microbe preferentially infects a certain cell type or area of the body
Why are point mutations more likely in some viruses?
The DNA pol or RNA pol carried/produce by viruses are more error prone than if they used a cell’s DNA pol
What type of viruses have the highest point mutation rate? Why?
RNA viruses b/e their RNA pol do not have proofreading abilities
What are quasispecies?
Species of viruses that are slightly dissimilar d/t point mutations
What is antigenic drift?
The selection of viruses like the flu which are able to evade the host immune system.
What are the two major ways in which viral genetics change?
- Recombination (for DNA only)
2. Reassortment
What is the recombination viral genetic change?
When two or more DNA viruses infect the same cell, and recombine their DNA utilizing enzyme within the cell
How do RNA viruses recombine their genome, if host cells do not have the machinery to recombine RNA?
Copy choice (when pol will abruptly stop one RNA chain mid protein and attach to another)
Reassortment (when segmented/different RNA is packeaged into viral envelopes)
What happens histologically to virus infected cells?
loss of cell-cell contact
What is a plaque assay?
Growing virus infected cells and looking for plaques to see if the virus is infectious
How is ELISA/wetern blot used to id viruses?
Western blot = size of protein
ELISA = search for antibodies
How is genome sequencing used to id viruses?
Use a primer in a PCR or RT PCR to detect viral DNA/RNA
What type of test would be used to detect viral antigens?
ELISA
What does the electon microscope used for in id viruses?
Looking at new viruses
