Mastering Biology Chapter 17
Which statements about viruses are true?
-HIV contains reverse transcriptase. -Enveloped viruses bud from the host cell. -The capsid enters the host cell if the virus is enveloped. -A retrovirus contains RNA.
Which of the three types of viruses shown in the figure would you expect to include glycoproteins as part of their overall structure?
1 and 2 only
Which of these binds to receptor molecules on the host cell membrane?
A
Which of the following events stimulates the production of viral particles in a host cell?
Activation of the host cell by cytokines, growth factors, or antigens.
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 nucleotides for transcription and replication. They must use a host cell's ribosomes to synthesize proteins. They must use a host cell's metabolic enzymes and pathways to obtain energy.
All of the listed responses are correct.
Which of these is reverse transcriptase?
C. (The little yellow dots)
Which of these is the viral genome?
E. (The purple squiggles inside)
Which viruses have single-stranded RNA that acts as a template for DNA synthesis?
E. Retrovirus
True or false? The human immunodeficiency virus (HIV) uses reverse transcriptase to make double-stranded RNA copies of its DNA genome.
False
How does HIV cause disease?
HIV kills cells that defend the body against disease.
In the figure, at the arrow marked II, what enzyme(s) are being utilized?
Host cell DNA polymerase
Which enzyme inserts viral DNA into the host's chromosomal DNA?
Integrase
What is the function of reverse transcriptase?
It catalyzes the formation of DNA from an RNA template.
What is the function of reverse transcriptase in retroviruses?
It uses viral RNA as a template for DNA synthesis.
Which replicative cycle describes a virus that can integrate its genome into the host cell's genome?
Lysogenic
Classify each phrase as applying to the lytic cycle, the lysogenic cycle, or both types of reproductive cycles of phages.
Lytic Cycle- the cell is lysed (broken open), new phages are assembled from viral DNA ad proteins, the host is destroyed Lysogenic Cycle- the cell reproduces normally, the viral DNA integrates into the chromosome of the host cell Both Cycles- viral genes are replicated
In the figure, when new viruses are being assembled (IV), what mediates the assembly?
Nothing, the proteins self assemble
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 enzyme is responsible for the process seen here?
Reverse transcription
Why is combination drug therapy for HIV/AIDS less likely to lead to resistance than single drug therapy?
The likelihood of one virus spontaneously mutating to be resistant to several different drugs at the same time is extremely small.
How does HIV bind to a host cell?
The viral envelope proteins interact with CD4 and a co-receptor on the cell membrane.
Which of the following statements about viruses is FALSE?
The widespread use of antibiotics has led to resistant strains of viruses.
How do enveloped viruses differ from nonenveloped viruses?
They have a membrane-like outer covering.
Why are retroviruses considered a special class of viruses?
They transcribe RNA to DNA using reverse transcriptase. (Retroviruses reverse the normal flow of information, forming a DNA provirus from an RNA genome.)
Most molecular biologists think that viruses originated from naked bits of cellular nucleic acid. Which of the following observations supports this theory?
Viral genomes are usually similar to the genome of the host cell.
Sort the items according to whether they may be found only in free virus particles, only in uninfected host cells, or in both viruses and host cells.
Viruses only- Capsid, Capsomere (core protein), Envelope with glycoproteins Host cell only- Ribosome Both- Protein, RNA, DNA
Which of the following can be found in bacteria, but not viruses?
a cell membrane
Which of the following statements correctly describes one characteristic of the lytic cycle of viral replication?
a large number of phage are released at a time
Suppose you were in charge of sending an unmanned space probe to a new planet in search of life. The probe would be able to collect and test samples and make observations, but the planet is too far away for the probe to be able to bring samples back to Earth. The probe is small and would only be able to run a few tests, so you want to pick a test for evidence of life that is broad enough to incorporate all forms of life as we know it. Which one of the following tests would be the best to use in this situation?
a test for the presence of cells that contain DNA
Homeostasis is a living organism's
ability to maintain constant internal conditions even when environmental conditions change.
Which of the three types of viruses shown in the figure would you expect to include a capsid(s) as part of their overall structure?
all 3
The nucleic acid of a virus particle is enclosed in a protein coat. What is it called?
capsid
Which of the following is why someone who has had a herpes virus-mediated cold sore or genital sore may have flare-ups for the rest of his or her life?
copies of the herpesvirus genome remaining as mini-chromosomes in some host cell nuclei
Which of the following is NOT a characteristic of living things?
creating energy
The pointer is indicating the virus's _____.
genome
What is the source of a viral envelope?
host cell membrane
Cycle A is the _____ cycle and cycle B is the _____ cycle. The figure shows two viral cycles A and B. During cycle A, virus enters the cell and replicates using the resources of the cell. Then numerous viral particles are released from the cell by lysis. During cycle B after the entrance and uncoating, viral genome integrates into the DNA of the cell and replicates with it.
lytic ... lysogenic
Viruses are
not alive because they are not made of cells and require a host cell for reproduction.
What is a virus that attacks a bacterium?
phage
Double-stranded viral DNA is incorporated into a host cell as a _____.
provirus
HIV uses which of the following processes to synthesize a DNA strand using its RNA genome as a template?
reverse transcription
The lytic cycle of bacteriophage infection ends with the _____.
rupture of the bacterium (The bacterium ruptures and phages are released.)
The genetic material of HIV consists of _____.
single stranded RNA
As a result of the lytic cycle, _____.
the host cell's DNA is destroyed -The host cell's DNA is destroyed, and ultimately, the host cell itself is destroyed in the lytic cycle.
Which of the following characteristics determine a virus's host range?
the proteins on its surface and that of the host
Which of the following responses correctly lists the order of events in a generalized viral replicative cycle?
the virus enters the cell, host enzymes replicate the viral genome, enzymes transcribe the viral genome into mRNA
Viral DNA makes mRNA by the process of _____.
transcription
In the lysogenic cycle _____.
viral DNA is replicated along with host DNA
The pointer is indicating the _____.
viral protein coat (head)
