Chapter 13 problem set

You discover a new medication that prevents the activity of RNA-dependent RNA polymerase. Which of the following will be affected by this medication?

Ebola virus Polioviruses

Please choose the term that describes a virus that has a lipid bilayer (derived from the host cell) surrounding its capsid.

Enveloped virus

Temperate phage.

Phage that is able to incorporate its genome into the host chromosome.

A bacteriophage initially associates with which bacterial structure?

The bacterial cell wall

Viruses with which characteristic would be expected to have a higher mutation rate?

RNA genome

Generalized transduction.

Transduction resulting from a packaging error.

Expression of viral oncogenes in infected animal cells

can mimic proto-oncogenes, causing imbalance in cell cycle control towards unchecked proliferation, leading to tumor formation.

Every virus particle contains ______.

either DNA or RNA

The mechanism of exit for an animal virus is primarily determined by whether or not the virus has a(n) _____.

envelope

The phages T4 (lytic) and lambda (temperate) share all of the following characteristics EXCEPT

existing as prophage

Once a phage becomes lysogenic, it will remain lysogenic and never be lytic again.

false

T-even phages can replicate independently of a host cell.

false

A major difference in the replication of animal viruses and bacteriophages is the ______ step.

penetration

Once inside the host cell, viral DNA directs production of _______.

new viral particles

Almost immediately upon entry, the viral nucleic acid alters the gene expression of the host cell.

true

What term describes the type of bacteriophage infection in which the host bacteria are lysed and killed as a result of the infection?

Lytic

When present, of what is the viral envelope composed?

Mainly lipids

Virulent phage.

Phage that lyses the bacterial host when completing its life cycle.

Which of the following about viruses/viral infections is FALSE?

Phages often enter a cell via receptor-mediated endocytosis.

Bacteriophage MS2 is an icosahedral, (+) sense, single-stranded RNA phage. It infects E. coli and other members of the Enterobacteriaceae. It only infects strains of these bacteria that have produced a sex pilus. Based on the information given, which of the following are true about MS2?

The bacterial receptor for MS2 is on the F (sex) pilus. MS2 is a virulent phage. The phage carries a replicase. MS2 can only infect F+ bacteria.

In the lysogenic stage of phage replication, the host cell is lysed.

false

Influenza viruses bud from the host cell. Based on this information, the viruses most likely

are enveloped

Some phages are medically important for all of the following reasons EXCEPT

they also infect eukaryotic cells.

Which of the following is an example of lysogenic conversion?

A lysogen that acquires new characteristics as a result of the prophage.

Immunity to superinfection (infection of a cell at a later time with a second, identical bacteriophage) is a consequence of lysogeny. Why does this occur?

A repressor produced by the first virus will actively suppress the lytic cycle of the second virus.

Which of the following is required to maintain a lysogenic state?

A repressor protein

Place the steps of T4 phage replication into the correct sequence

Attachment—phages attach to receptors on bacterial surface. Genome entry—phage tail contracts and phage DNA is injected into bacterial cell. Synthesis—phage genome is transcribed and translated; phage DNA is replicated. Assembly—newly synthesized phage components are assembled into mature virions. Release—bacterial cell lyses, releasing new infectious virions.

Which of the following descriptions fits a chronic viral infection?

Characterized by continuous production of low levels of viral particles, potentially even in the absence of active symptoms of disease. The organism is usually still highly infectious during this time.

Acute infection.

Infection in which a virus multiplies rapidly and spreads in the host.

How does bacteriophage DNA get into the host cell?

It is injected.

Which of the following describes a latent viral infection?

Long periods of time with essentially zero viral replication, punctuated by outbreaks of active replication and disease manifestation. Infected individuals are largely non-infectious between outbreak periods.

What term describes the type of bacteriophage infection cycle where the bacteriophage DNA is inserted into the host cell DNA as a prophage and the infected bacteria can continue to grow and divide?

Lysogenic

Which of the following characteristics can be utilized to classify and categorize viruses?

Type of nucleic acid Hosts infected Strandedness of nucleic acid (positive/negative sense) Capsid shape Presence or absence of envelope Disease symptoms

Which of the following can cause a phage in the lysogenic stage to revert to the lytic stage?

Ultraviolet light

A consequence of the temperate life cycle is lysogenic conversion. What does this term mean?

When a bacterial cell starts to produce a new phage protein (e.g., diphtheria toxin) after the viral genome inserts into the host genome.

The capsid of a virus is

a protein shell that surrounds the nucleic acid

The general steps in viral replication (in order) are

adsorption, penetration, synthesis, assembly, release.

A virus usually infects only certain types of cells due to

interactions between viral and cellular surface molecules.

The final step in T2 bacteriophage infection results in:

lysis of the bacterial cell and release of new viral particles

After beta phage infects Corynebacterium diphtheriae and integrates its DNA into the host genome, the bacterium is capable of causing the disease diphtheria. Which term best describes this phenomenon?

lysogenic conversion

Viral cycles that end in release of the new phages and immediate destruction of the host bacterial cell are referred to as ______.

lytic

Viral capsids are composed of ______.

protein

Phage DNA encodes for the proteins of the viral capsid and

regulatory proteins that direct the production and assembly of the capsid proteins

All of the following could serve as receptors for phage attachment EXCEPT

ribosomes.

The enzyme lysozyme is used by the T4 phage to assist in the injection of its DNA into the target cell.

true

Removal of the capsid to release the virus nucleic acid into the host cytoplasm is called ______.

uncoating

Rabies virus, which can be transmitted from animals to humans, is classified as a(n) ______ virus.

zoonotic

Which of the following is used to classify viruses? i. Nucleic acid ii. Shape iii. Size iv. Host range v. Biochemical tests

(i), (ii), (iii), and (iv)

Which of the following contains only one type of macromolecule? i. RNA viruses ii. DNA viruses iii. Prions iv. Viroids v. RNA and DNA viruses

(iii) and (iv)

What bacterial enzyme is used by the virus for replicating its nucleic acid?

DNA polymerase

In lytic phage infections, the early viral proteins are important for initial steps of phage multiplication. Which of the following are functions of these proteins?

Degrade host cell's DNA. Modify host cell's RNA polymerase so that it doesn't recognize bacterial promoters.

Specialized transduction.

Transduction resulting from an error in excision of a prophage.

Please choose the statement that best describes the role of viral surface proteins or spikes.

Viral spikes provide means of attachment to host cell surface.

Viral spikes

attach specifically to host cell receptors

The stage of T4 replication that involves interaction between the protein fibers on the phage and receptors on the bacterial cell wall is the

attachment stage.

Bacteriophage DNA directs the degradation of the bacterial host cell's DNA.

true

The T-even bacteriophages such as T2 and T4 infect

Escherichia coli.

In viral entry by endocytosis

the host cell's cytoplasmic membrane surrounds the whole virion and forms a vesicle.

A bacterium being examined in a microbiology laboratory is found to be lysogenized by phage A. Which of the following statements is TRUE?

The bacterium exhibits a new genotype but may not exhibit a new phenotype.

Which of the following characterizes phage but NOT eukaryotic viruses?

The genome, but not the protein coat, enters the cell. They may be involved in generalized or specialized transduction.