19.1
What is the function of reverse transcriptase in retroviruses?
It uses viral RNA as a template for DNA synthesis
What molecule makes up the viral envelope?
Glycoproteins
Most human infecting viruses are maintained in the human population only. However, a zoonosis is a disease that is transmitted from other vertebrates to humans, at least sporadically, without requiring viral mutation. What is the best example of zoonosis?
Rabies
Why do RNA viruses appear to have higher rates of mutation?
Replication of their genomes does not involve the probreading steps of DNA replication
Given Baltimore's scheme a positive sense single stranded RNA virus such as polio virus would be most closely related to...?
Retroviruses that require a DNA intermediate
What characteristics of electron microscopes make them the most useful for studying viruses?
Shorter wavelengths provide higher resolution
Describe the lysogenic cycle of the Lambda Phage.
The phage genome replicated along with the host genome
Why are viruses referred to as obligate parasites?
They cannot reproduce outside of the cell.
What is a characteristics of the lytic cycle?
a large number of phages is released at one time
In many ways, the regulation of the genes of a particular group of viruses will be simiular to the regulation of the host genes. Therefore, what would you expect of the genes of the bacteriophage?
control of more than one gene in an operon
What accounts for someone who has had a herpesvirus-mediated cold sore or genital sore getting flare ups for the rest of life?
copies of the herpesvirus genome permanently maintained in host nuclei
What can be effective in preventing viral infection in humans?
getting vaccinated
What term describes bacteriophage DNA that has become integrated into the Host cell chromosome?
prophages
What is the most probable fate of the newly emerging virus that causes high mortality in its host?
the newly emerging virus will die out rather quickly or will mature to be far less lethal.
What series best reflects what we know about how the flu virus moves between species/
An animal such as a pig is infected with more than one virus, genetic recombination occurs, the new virus mutates and is passed to a new species such as a bird, the virus mutates and can be transmitted to humans.
Viral envelopes can best be analyzed with what technique?
Antibodies against specific proteins not found in the host membranes
If you already knew that the infectious agent was either bacterial or viral, which treatment would allow you to distinguish between these two possibilities?
Culturing the substance by itself on nutritive medium , away from any plant cells.
Antiviral drugs that have become useful are usually associated with...?
Intereference with the viral reproduction
Viral genomes vary greatly in size and may include from four genes to several hundred genes. What viral features are most apt to correlate with the size of the genome?
Size and shape of the capsid
The host range of a virus is determined by?
The proteins on its surface and that of the host
A researcher lyses a cell that contains nucleic acid molecules and capsomeres of tobacco mosaic virus. the cell contents are left in a covered test tube overnight. the next day this mixture is sprayed on tobacco plants. What could occur?
The plants may develop the typical symptoms of TMV infection
What represents a difference between viruses and viroids?
Viruses have capsids composed of protein, whereas viroids have no capdids
Most molecular biologists think that viruses originated from fragments of cellular nucleic acid. What observation can be made that supports this theory?
Viral genomes are usually more similar to the genome of the host cell than the genomes of viruses that infect other cell types.
What is the best predictor of how much damage a virus causes?
ability of the infected cell to undergo normal cell division
What are prions?
misfolded versions of normal brain protein
What is the name given to viruses that are single stranded RNA that acts as a template for DNA synthesis?
retroviruses
What describes plant virus infections?
they are spread throughout a plant by passing through the plasmodesmata
the difference between vertical and horizontal transmission of plant viruses is that
vertical transmission of a virus from a parent plant to its progeny, and horizontal transmission is one plant spreading the virus to another plant.
Treating the substane with ucleases that destroy all nucleic acids and then determining whether it is still infectious is a treatment that could determine...
whether or not the component is viroid
