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Flashcards in Virology ( Dr. Balfe) Deck (34):

History of Virology:
- Edward Jenner (1749-1823) ?

- introduced cowpox vaccination for smallpox


History of Virology:
- Martinus Beijernck discovered what? (1851-1931)

-he discovered viruses by selectively filtering; thereby, showing the presence of an infectious agent smaller than bacteria
- He also showed that they operated in association with cells


History of Virology:
- Wendell Stanley - what's his story, yo? (1904-1971)

- he showed that viruses were particulate


History of Virology:
- Fred Sanger (1981-) discovered what?

- the first complete genome sequence
- Bacteriophage lambda174 (5,386bp)


What are the requirements of life? (5)

- communication
- movement
- metabolism
- reproduction


Do viruses need the same five requirements of living things?

- only reproduction


Explain how viruses are dependent on the host. (5)

- replication cannot be done on their own
- they do not have cells
- they cannot produce ATP or utilize nutrients of any sort
- synthesis of proteins, nucleic acids etc cannot happen. They are not capable of synthesizing anything
- They completely depend on the cell they infect for all of the above f(x)s via modifying the host machinery


All organisms contain RNA and DNA but what about viruses?

- they contain RNA OR DNA.


What are the seven viral groups. Give examples within each.

Group 1: dsDNA Viruses -> Herpesvirus family (HSV, CMV, EBV and friends)
Group 2: ssDNA Viruses -> Parvovirus
Group 3: dsRNA Viruses -> Rotaviruses
Group 4: (+) sense RNA Viruses -> HCV, polio, FMDV
Group 5: (-) sense RNA Viruses -> Influenza, Ebola
Group 6: RNA Reverse Transcribing Viruses -> HIV (Retroviruses)
Group 7: DNA Reverse Transcribing Viruses -> HBV ( DNA retroviruses)
L> this is an extremely small group


Give a run through of a dichotomous key for RNA Viruses.

1. Single stranded or double stranded?
IF SS ---> antisense or sense? If it is anti = group 5 aka antisense RNA viruses
IF it is sense.....does it have reverse transcriptase or not? If yes...Group 4 aka + sense RNA Viruses .. If no = Group 6: RNA Reverse Transcriptase Viruses

IF DOUBLE STRANDED IT = Group 3 = dsRNA Viruses


Give a run through of a dichotomous key for DNA Viruses. So obv.

- SS or DS
- If SS = Group 2= ssDNA Viruses
- If DS = Group 1 = dsDNA Viruses


Explain the difference between prions and viroids.

- Viroids= very small (200 to 400 nt) rod like RNA molecules, only plant pathogens (ex: potato spindle tuber viroid)
-Prions= They do not have any nucleic acid. They are very resistant to heat inactivation, resistant to radiation damage, resistant to DNAse and RNAse treatment. They are sensitive to urea, SDS, phenol and other protein denaturing chemicals.


Are viroids and prions considered viruses?

- no because they are either or situations
- one with only proteins
- one with only nucleic acid
- Viruses however have BOTH.
- Therefore these can be used to determine a virus type


Give the working definition of a virus

- An obligate intracellular parasite
- OR: A bit of bad news wrapped up in a protein


What protects the nucleic acid present in viruses?

- capsids! (protein coat)


What are the three types of capsids we examined in lecture?

1. Simple shapes seen in viruses such as Tobacco mosaic virus, Adenovirus and Smallpox
2. Helical Capsid
3. Icosahedral Capsid


What proteins are involved with capsids?

- histolike proteins that bind to the nucleic acid
L> Acids interact with bases...histolike proteins tend to be basic


Which of the three capsid types is the most efficient?

- an icosahedron is the most efficient way to make a sphere out of planes
- 20 triangles arranged in a sphere


Can a virus have more than one type of capsid structure?

- Ex: T4 Bacteriophage ...has both icosahedral and helical capsids.


Are viruses often classified by their shape?

- unlike bacteria, viruses CANNOT be classified by shape.


Which of the following cell interactions hold true with viruses:
1. Viruses all use specific receptors
2. Viruses have to reach the nucleus to replicate
3. Viruses require host cell energy
4. The same viruses can infect humans and plants

1. many do but not all
2. most DNA viruses do have to
L> no viruses jump kingdoms - duh


Virus Replication Cycle:
- What are the four steps?

- Entry
- Replication
- Assembly
- Release


Virus Replication Cycle:
- Which step is a major determinant of tropism?

- Attachment and penetration


Which step in the virus replication cycle is a major determinant of pathogenesis?

- Release


Are RNA and DNA always protected by nuclear proteins?

- they are never just free floating


Virus Replication Cycle:
- Explain attachment and tropism (ex?)

- Receptors define tropism, if a cell lacks the receptor, it can't be infected
- Ex: 2-6 sialic acid is the receptor for human flu, 2-3 sialic acid is the receptor for bird flu. Pigs have BOTH molecules in their lungs. This is how so many new strains of flu can develop over time because within the pig they mix.


Virus Replication Cycle:
- Explain penetration.

- It can be either fusion from within which is pH dependent OR it can be fusion from without which is pH independent
-some viruses can do both
-fusion from within = endocytosis
-fusion from without is done via receptors


Virus Replication Cycle:
- Explain the 1 step Growth curve

-when the virus is added there is a latency period (eclipse and maturation). As assembly and release occur there is a spike in the curve after which it levels off.


Virus Replication Cycle:
- The model of lytic infection consists of three periods:
1. Eclipse
2. Maturation/ Release
3. Plateau
- Explain each of these.

1. all of the virus is absorbed, plateau period when no detectable virus present, virus count = 0, infection appears latent, virus synthesis within cell.
2. Rapid increase in count as infected cells lyse, releasing virion
3. post release plateau, all infected cells in culture lysed.
- In real life this is more complex however this can occur with bacteriophage and bacteria.


Virus Replication Cycle:
- When is the 1 step growth curve able to detect viral growth?

- only under special conditions
- aka synchronous cultures infected with virus at an MDI of


Virus Replication Cycle:
- Explain the process of release.

- After the virus is assembled it is shipped to the outer membrane to be released via viral budding. Maturation occurs and the protease cleavages and condensation of nucleocapsid also occurs


Virus Replication Cycle:
- Release can take two forms. What are they?

- Viral budding
- Chronic release ( this can take a while)


Virus Replication Cycle:
- Explain the trainspotter fact

- viruses that replicate by bursting cells (lytic infection) tend to be naked particles, that is - just a capsid with spikes.
- Viruses that bud chronically from sick cells tend to pick up a membrane as they leave so are called enveloped.


What is different about the viruses that are enveloped vs non? How does it aid in chronic or lytic infection?

- Enveloped viruses ( HSV, Flu, HCV etc) are quite different in appearance from the non-enveloped viruses (Polio, adenoviruses, HPV etc). It's still an icosahedron but the enveloped viruses often look like an icosahedron in an old polythene bag. SO a quick look at an EM of the virus can give a strong hint as to whether that virus causes chronic or lytic infection.