Chapter 19 HW: Viruses - Biology II
How do prions, which are misfolded proteins, infect organisms?
Prions enter brain cells and cause normal forms of the protein to refold into the prion form.
What is the genetic material of retroviruses?
RNA
What describes the lysogenic cycle of lambada phage?
The phage genome replicates along with host genome.
A plant that has been raised in sterile environment shows symptoms of a viral infection. How would you explain this?
The viral infection was acquired by vertical transmission.
What represents a difference between viruses and viroids?
Viruses have capsids composed of protein, whereas viroids have no capsids.
Why are retroviruses considered a special class of viruses?
They transcribe RNA to DNA using reverse transcripts.
H.I.V. evolved from a virus that infects what species?
chimpanzee
The H1N1 2009 outbreak is considered to have been which of the following?
a pandemic
Your dog is lacking syncytin. It will not be able to properly form what?
a placenta
You are an epidemiologist studying a new disease very similar to AIDS. Most likely, this new disease is caused by what?
a retrovirus
What accounts for someone who has had a herpesvirus-mediated cold sore or genital sore getting flare-ups for the rest of his or her life?
copies of the herpesvirus genome permanently maintained in host nuclei
How long must AIDS patients take their medication?
for the rest of their life
What characteristics, structures, or processes is common to both bacteria and viruses?
genetic material composed of nucleic acid
What is the source of a viral envelope?
host cell membrane
The genetic material of HIV consists of ____________________.
single-stranded RNA
The host range of a virus is determined by
the proteins on its surface and that of the host.
Emerging viruses arise by
the spread of existing viruses to new host species, mutation of existing viruses, and the spread of existing viruses more widely within their host species.
Viral DNA makes mRNA by the process of ______________.
transcription
Approximately how many people worldwide are infected with AIDS?
60 million
What is characteristic of the lytic cycle?
A large number of phages are released at a time.
What 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.
What is the function of reverse transcripts?
It catalyzes the formation of DNA from an RNA template.
Explain why studies of fossil viruses help biologists understand the process of human evolution.
It is believed that over 8% of the human genome can be traced back to infections by retroviruses. By learning more about these viruses, scientists will have a more complete picture of how the human species evolved its current genome.
What is the most probable fate of a newly emerging virus that causes high mortality in its host?
The newly emerging virus will die out rather quickly or will mutate to be far less lethal.
Why are viruses called obligate intracellular parasites?
They must use a host cell's amino acids to synthesize proteins. They must use a host cell's metabolic enzymes and pathways to obtain energy. They must use a host cell's nucleotides for transcription and replication. They must use a host cell's ribosomes to synthesize proteins.
Viral envelopes can best be analyzed with what technique?
antibodies against specific proteins not found in the host membranes
AIDS can be contracted by contact with which of the following?
blood or semen
Antiviral drugs that have become useful are usually associated with what property?
interference with viral replication
A researcher lyses a cell that contains nucleic acid molecules and capsomeres of tobacco mosaic virus (TMV). The cell contents are left in a covered test tube overnight. The next day this mixture is sprayed on tobacco plants. What would be expected to occur?
it would develop the typical symptoms of TMV infection.
What do we call a virus that attacks a bacterium?
phage
Double-stranded viral DNA is incorporated into a host cell as a _____________.
provirus
What is the most effective way to stop viral infections?
vaccines
The difference between vertical and horizontal transmission of plant viruses is that
vertical transmission is transmission of a virus from a parent plant to its progeny, and horizontal transmission is one plant spreading the virus to another plant.
In the lysogenic cycle __________________.
viral DNA is replicated along with host DNA
