CHAPTER 13: REVIEW QUESTIONS

Viral infections that result in the formation of new virus particles are described as which of the following types of infections? a) primary b) productive c) horizontal d) lateral e) latent

b) productive

What are viruses that infect bacteria?

bacteriophages phages

What directs the incorporation of phage DNA into a bacterial chromosome

integrase

What is meant by a defective phage head?

specialized transduction -temperate phage - when transitioning from a lysogenic state to a lytic state sometimes part of the bacterial DNA is taken on each side of the phage DNA during excision - thus containing both bacterial and phage genes they replicate and develop into phage heads these heads are defective because they do not carry the entire set of phage genes

In tissue culture, why is it advantageous to use tumor cells rather than normal cells?

normal cells from animal tissues are slow can only divide a certain number of times even when diluted into fresh medium thus fresh medium needs to constantly be added to avoid this problem- tumor cells are often used in cell culture these cells divide indefinitely in vitro resulting into an established cell line

At a minimum all viruses are composed of what?

nucleic acid protein

Because they are dependent on host cells, viruses are classified as what?

obligate intracellular parasites

What is used to describe the phage DNA that is latently incorporated into the bacterial host genome?

prophage

In which stage of viral multiplication would you expect to see "budding" occur?

release

Which protein is essential for the maintenance of the lysogenic state?

repressor

What is specialized transduction?

result of excision errors

What is generalized transduction?

result of packaging errors during the assembly stage of phage replication

What phages enter the prophage state?

temperate

Symptoms of acute viral diseases result from what?

host tissue damage host immune response

Consequences of lysogeny include what?

immunity to superinfection lysogenic conversion

A viral genome can consist of either _________ stranded or ________ -stranded nucleic acids

single double

T/F: Bacteriophages are important medically because they prevent growth of food contaminating bacteria

True

What are plaque forming units?

each plaque represents a plaque-forming unite (PFU) initiated by a single phage particle infecting a cell

What is the function of proto-oncogene?

genes that stimulate cell growth

Why are virally encoded enzymes medically important?

because they represent potential sites for the action of antimicrobial medicines. The medicines would not likely have any harmful effects on the host cells.

In which ways do newly assembled viruses leave their host cell?

budding apoptosis

The number of phage particles released from a host cell is called a _________ size

burst

Which term is used to describe the phospholipid bilayer found surrounding the capsid of some viruses?

envelope

What are characteristics of specialized transduction?

errors occur in excision of prophage transfers phage DNA and adjacent host genes produces defective phage particles

In __________ transduction, only bacterial genes adjacent to the prophage can be transferred; and in ___________ transduction any bacterial gene can be transferred.

generalized specialized

The protection of lysogens against infection by the same phage is provided by the repressor protein that will bind to the _________ on incoming phage DNA, preventing expression of the phage genes

operator

Rank smallest to larges: Human Cells Bacteria Viruses

1) Viruses 2) Bacteria 3) Human cells

Replication of temperate phages and lytic phages have which steps in common?

Genome entry Biosynthesis of viral components Attachment Release Assembly

Explain why a vaccine can prevent cervical cancer?

HPV encoded proteins appear to interfere with the function of the tumor suppressor gene product the vaccines protect against these virus proteins before they take effect

Which are two major categories of viral infections?

acute persistent

Distinguish between acute and persistent infections at the cellular level

acute - release of virions from infected host cell virus-infected cells often die and host survives immune system of animal host may gradually eliminate the virus over a period of days to months persistent - remain for years or life of host without any symptoms 2 types - chronic & latent chronic - low production of viral particles latent - viral genome remains silent in host but can be reactivated and cause a productive infection

Which of the following are bacterial defenses against phase infection?

altering receptor sites CRISPR system restriction modification systems

In order to infect an animal cell, viruses do what?

attach to receptors on the host cytoplasmic membrane

How are latent viral infections different than chronic ones?

chronic - low production of viral particles often do not produce symptoms cell may survive or lyse - person can transmit virus even in the absence of symptoms latent - viral genome remains silent in host but can be reactivated and cause a productive infection silent viral genome = provirus provirus cannot be eliminated from body and can recur years later

Which of the following is not a classification of bacteriophage based on the type of infection they produce in host? a) temperate phage infections b) lytic phage infections c) filamentous phage d) complex phage

d) complex phage

Enveloped viruses acquire their outer covering

from the host cell cytoplasmic membrane

What is it called when bacterium acquires new traits due to the prophage it carries?

lysogenic conversion

Most temperate phages integrate into the host chromosome, whereas some replicate as plasmids. Which kind of relationship would you think would be more likely to maintain the phage in the host cell, why?

lysogenic infection is more likely to maintain the phage in the host cell - the infected cell is called a lysogen the phage DNA exists within the host cell without causing damage the integrated phage DNA - prophage - is replicated along with the host cell chromosomes the phage DNA is more likely to become lost during replication or cell division

What phages burst the host cell shortly after infection?

lytic

How do enveloped viruses exit a cell?

most enveloped viruses exit via budding a process whereby the virus acquires its envelope before budding occurs, protein spikes insert into specific regions of the host's cells membrane matrix protein accumulates on the inside surface of those same regions that the spike proteins attached assembled nucleocapsids are then extruded from the cell at these regions -- becoming covered with a layer of matrix protein and lipid envelope in the process

Why would it be advantageous to a virus to interfere with the function of proto-oncogenes or tumor suppressor genes?

mutations that result in inappropriate timing or level of expression with proto-oncogenes or tumor suppressor genes can lead to uncontrolled and abnormal cell growth thus more cells would be produced = more cells that could be invaded by the viruses leading to increased virus production

Why can viruses not replicate independently of living cells?

they don't have any of the structures, such as ribosomes required for protein synthesis and the machinery required for harvesting energy.

What are two traits of viruses?

they have capsids made of protein they contain either RNA or DNA

What occurs with viruses by fusion?

virus envelope fuses with cytoplasmic membrane

Is it important to have fewer phages than bacterial host cells when doing a plaque quantitative plaque essay?

yes, because to measure the number of phage requires that only a single virion infect a bacterial cell if there were fewer bacteria than phage particles, more than one virion would infect the same bacterium - only a single plaque would result.

Discuss two methods used to quantitate animal viruses

plaque assay -titer can be estimated -several dilutions of the virus preparation are administered to a number of animal, cells, or chick embryos -titer (endpoint) is at which 50% of the inoculated hosts are infected or killed hemagglutination -certain viruses cause RBC to agglutinate -occurs when viral particles attach surface molecules of multiple RBCs -cells form aggregate -visible only at high concentrations of viruses

Which is more likely to be a specialized transducing phage- a lytic or temperate phage?

specialized transduction results from an excision mistake made by a temperate phage made during its transition from a lysogenic state to a lytic cycle

How might syncytia formation of infected cells benefit viruses?

the fusion of infected cells with uninfected cells would allow viruses to infect additional cells and not be subject to the defense mechanisms of the body

Could the same type of virus cause both an acute and latent infection? Explain

yes, the initial infection might be acute but the virus can later become latent by becoming integrated into the host cell genome Example: herpes initial HSV-1 causes an acute infection in mucosal epithelial cells (cold sores) then travels to sensory nerve cells where it remains latent