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SJSU Virology


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Name the four historical developments in Virology.
1. Discovery of first virus
2. Biochemical analysis
3. Molecular analysis
4. Recombinant techniques
Which vaccines and their creators where created before the discovery of viruses?
Smallpox - Jenner
Rabies - Pastuer
Explain the Hershey-Chase experiment.

Side by side experiments are performed with separate bacteriophage (virus) cultures in which either the protein capsule is labeled with radioactive sulfur or the DNA core is labeled with radioactive phosphorus.

1. The radioactively labeled phages are allowed to infect bacteria.
2. Agitation in a blender dislodges phage particles from bacterial cells.
3. Centrifugation concentrates cells, separating them from the phage particles left in the supernatant.


1. Radioactive sulfur is found predominantly in the supernatant.
2. Radioactive phosphorus is found predominantly in the cell fraction, from which a new generation of infective phage can be isolated.

Conclusion: The active component of the bacteriophage that transmits the infective characteristic is the DNA. There is a clear correlation between DNA and genetic information.
Would you characterize the Hershey-Chase experiment as biochemical analysis or molecular analysis?
Name the three theories of the origins of the virus?
1. Regressive theory
2. Modification theory
3. Co-evolution theory
What is the regressive theory of virus origination?
From a free living organism

* Moved into a cell
* Progressive loss of metabolic functions and genetic material
* Becomes an obligate intracellular parasite
What is the modification theory of virus origination?
From host cell mRNA

* Self-replicating RNA from host cell mRNA
* Self-splicing RNA from the self-replicating RNA
* Never had metabolic functions
* Exists as an obligate intracellular parasite
What is the co-evolution theory of virus origination?
Mixture of DNA, RNA, proteins, carbohydrates

* Complex polymers form at the same time that cellular life evolved. (Coevolution)
* Moves into a cell
* Becomes an obligate intracellular parasite
What are the major differences between bacteria and non-enveloped DNA virus?
1. The virus is constituted of only DNA and protein.

2. The bacteria is constituted of lipid, polysaccharide, ions/molecules, RNA, and also DNA and protein.
Describe the differences in viral and cellular growth characteristics.
Bacterial and cellular growth patterns are exponential. They have a lag, log,, plateau, and death cycle.

Viruses do NOT have exponential growth patterns but can be best described as "burst". The cycle is eclipse and then burst.

* One virus infects host cell
* Many virus particles are assembled
* Many are released from host cell
How does the viral genome differ from the genome of other organisms?

1. One type of nucleic acid only (DNA or RNA)

2. Circular or linear genome

3. One piece or multiple piece genome

4. Strandedness: can be ssDNA, dsDNS, ssRNA, dsRNA

5. Polarity: ss nucleic acids can be a (+) or (-) strand, ds nucleic acids has one strand of each (+ and -).
What are the average MW of one amino acid, one nucleotide base, and one base pair?
Amino acid: 110
Nucleotide: 350
Base pair: 700
Virus are smaller than this cell organelle.
What is a protein subunit?
Just a single protein on each side of a (triangular) face
What is a structural unit?
Can be a protein subunit and is on each side of a face

** Can be made up of more than one protein
What is a capsomer?
The structure observed on the outside of virus particles after negative staining AND only under the electron microscope
What is a capsid/coat/shell?
All described the outer protein structure encasing the nucleocapsid
What is a nucleocapsid?
The helical nucleic acid associated with protein subunits

** Also known as the core
What is an envelope?
Was once the lipid of the host cell in which the virus was assembled
What are spikes?
Proteins protruding through the envelope
What is a virion?
A complete virus particle with its DNA or RNA core and protein coat as it exists outside the cell.
Icosahedral symmetry has how many axes of rotation?

What are they and how many degrees of the circle for each triangle?

5 fold axis: 72 degrees
3 fold axis: 120 degrees
2 fold axis: 180 degrees
What are the three types of symmetry available to viruses?
Helical, icosahedral, and complex.
Which of the viral symmetries is the major structural arrangement?

Present one viral example of this structure.

What is the function of the capsid?
1. Protect nucleic acid genome from damage and degradation by nucleases

2. The outer surface recognizes and interacts with the host cell by binding of its proteins to cell receptor

3. Initiates infection by delivering genome in a form that interacts with host cell
What four properties are used to classify viruses?
1. Type of nucleic acid (DNA or RNA)

2. ss or ds

3. enveloped or non-enveloped

4. type of symmetry

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