Viral Structure and Fxn Flashcards
What are the basic properties of Viruses?
- Core Nucleic Acid surrounded by Protein Coat.
- Cannot replicate on their own. Need host.
- Do undergo self assembly
How do viruses “survive?”
- House DNA/RNA in CAPSIDS
- DNA/RNA contain information to initiate and complete an infectious cycle
- Infect hosts (either benign, or lethal)
All viruses have the same process of survival, but there its tons of diversity as to how it is accomplished.
What are the two systems for classifying viruses?
- Classical System (based on physical properties)
2. Baltimore System (based on mRNA production route)
What are the categories used to classify viruses in the Classical System?
- DNA/RNA
- Symmetry of the capsid (helical or icosahedral?)
- Naked (non-enveloped) or Enveloped
- Dimensions of virion or capsid
What are the 4 types of processes used to produce viral genetic material in hosts? (Baltimore classification)
- dsDNA (transcribed directly by host machinery)
- ssDNA (need to have a double-stranded intermediate)
- Retroviruses ssRNA with DNA intermediate. Are integrated into the host DNA.
- ssRNA can be directly translated by the host ribosome
What is the difference between direct and indirect fluorescence antibody imaging for viruses?
Direct- Anitbody binds DIRECTLY to viral antigen.
Antibody (with probe)——Viral antigen
Indirect- Antibody binds to antiviral antibody, which is bound to the viral antigen.
Antibody (with probe)—–Antibody——Viral antigen
What is the basic structure of a virus?
- Capsid (protein coat)
- Envelope (membrane from host)
- Genome
What is the difference between a helical and a icosahedral capsid?
Ones helical the other is not….. But really
An icosahedral capsid is made up of 20 isosceles (get it?) triangles that come together to form a pseudo sphere. Think of a soccer ball, but with triangular faces.
True or false: Icosahedral capsids always contain RNA.
True… according to the wiki.
But I bet you thought it was false because of the ALWAYS huh? Sucks to suck.
For what its worth, whats the least amount of subunits you can have? 60, making 20 triangular faces.
What are the 7 types of basic Virus genomes?
- dsDNA
- ssDNA
- Gapped Circular DNA
- ssRNA (+)
- ssRNA (-)
- dsRNA
- ssRNA (+) w/ DNA intermediate: AKA Retrovirus
How do gapped circular DNA viruses, such as hepatitis B, replicate their DNA?
- The circular DNA is transcribed in nucleus.
- mRNA is translated to produce a reverse transcriptase.
- RT creates new Circular DNA
True or false:
All RNA viruses encode for a RNA-dependant RNA polymerase.
True! Did I get you again?
All RNA viruses encode an RNA dependent RNA polymerase RdRp. Whether or not they needed it is a different story.
Generally, dsDNA viruses replicate their DNA in _________. Except _________ viruses, which replicate in the ______________.
Generally, dsDNA viruses replicate their DNA in nucleus. Except poxviruses, which replicate in the cytoplasm. They use their own RNA pol.
Which RNA virus is translated directly by host organelles?
ssRNA (+)
Think of the +/- as “ribosome ready RNA”
Which RNA virus is transcribed directly by host organelles?
ssRNA (-)
Think of the +/- as “ribosome ready RNA”
Which RNA virus relies most heavily on RNA dependant RNA polymerase?
ssRNA (-)
It needs to get to ssRNA + to be translated
How do retroviruses work? Are they single or double stranded?
ssRNA (+)
They use Reverse Transcriptase to generate dsDNA. The DNA then is integrated into the host genome where it is transcribed.
What are the steps in a generalized replication cycle of a virus?
- Eclipse Period (viruses are not infectious during this period)
- Latent Period
T/F:
Viruses replicate in an exponential pattern similar to bacteria.
FALSE:
Viruses are produced in “bursts” of fully formed virions.
What happens in the Eclipse period of a viral cycle?
It is the time where the virus has broken down inside of a cell and has released its genome.
What happens in the latent period of a viral cycle?
It is the time it takes from initiation of an infection to the release of new infectious virus particles from the cell
What are the 7 steps in the latent period of a viral cycle?
- Attachment of Virus to Cell
- Entry
- Release of Genome
- Viral Gene Expression
- Viral Gene Replicaiton
- Assembly of new viruses
- Release (egress) of viruses
How does a virus attach to a cell?
Viral proteins usually attach to glycoproteins or glycolipids on cell membrane.
Although there are no set “rules” for what it can or can’t attach to.
What is the difference between a susceptible cell, a resistant cell and a permissive cell?
- Susceptible- has functional receptors, may or may not replicate virus
- Resistant- Lacks functional receptors, may or may not replicate virus
- Permissive- Can Replicate virus, may or may not be susceptible
In order for replication to happen, a cell must be BOTH SUSCEPTIBLE and PERMISSIVE.
Which type of Virus has the ability to fuse to a cell membrane, enveloped or non-enveloped?
Enveloped Viruses contain a plasma membrane envelope. This allows for direct membrane fusion with a host.
True/False: Endosome formation can occur in both enveloped or non-enveloped viruses?
True.
Assembly of new viruses is the 6th step in the cycle. What are the 2 types of assembly that can occur? What are characteristics of each one?
- Icoshedral Capsid assembly
- Capsid may form around viral genome OR the genome may be fed INTO a preformed capsid. - Helical Capsid assembly
- Helical capsid assembly occurs DURING synthesis of the viral genome.
How do enveloped and non-enveloped viruses egress from a cell?
- Enveloped viruses egress by “budding” from either the Golgi (secretion) or from the plasma membrane (direct release)
- Non-enveloped viruses egress via LYSIS. Lysis occurs when so many virions are produced, the cell ruptures.
