As a consequence of infection by a temperate bacteriophage such as lambda, and a host cell
may lyse of may continue to divide and replicate both itself and the prophage
All of the following can act as receptors for various bacteriophages EXCEPT
cilia
Cellular receptors may be composed of
combinations of proteins, carbohydrates, and/or lipids
The term phage is generally reserved for the viruses that infect
bacteria
What structural can the viral genome take?
ss-DNAds-RNAds-DNA
The growth of viruses in a culture is described as a one-step growth curve, because
virion number show no increase during intracellular replication and can only be counted after the virion burst from the host cell
A virus that kills its host is said to be
lytic or virulent
Regarding the viral membrane of an enveloped virus, the lips are derived from the ________, and the proteins are encoded by _______.
hosts cell membrane / viral genes
Restriction is
a general host mechanism to prevent the invasion of foreign nucleic acid
The size and shape of viral particles is largely governed by the size and packaging of the viral
genomes
What would be the consequences of deleting the late T4 genes?
T4 capsid proteins would not be made
Retroviruses are medically important viruses because
they include some viruses that cause cancer and HIV
Considering T4 bacteriophage infection of a bacterial cell, which would be an example of the earliest phage proteins transcribed and translated?
enzymes for the synthesis and glucosylation of the unusual T4 base 5-hydroxymethylcytosine
The T4 phage protects its DNA from host restriction endonucleases by
glucosylating cytosine bases in the T4 genome to prevent DNA cleavage
What are the possible consequences of viral infection of an animal cell?
Outcomes vary from rapid lysis to persistent infections, latent infections, or cancer
Enveloped viral membranes are generally _______ with associated virus-specific _______.
lipid bilayers / proteins
You are attempting to mutate lambda to affect whether lysis or lysogeny occurs after infection. Which mutation would INCREASE the chances of LYSOGENY over lysis?
deletion or inactivation of the cro gene
A prophage replicates
along with its host while the lytic genes are not expressed
In E. Coli, the adenine in the sequence GATC is methylated by the Dam enzyme. In the same cells, a restriction endonuclease recognized and cleaves dsDNA with the sequence GATC on either strand. Why does E. Coli have these two enzymes?
The enzymes protect E. coli from infection by preferentially degrading viral or other exogenous DNA that is not methylated
The genome of retroviruses contains genes to make all of the following EXCEPT
repressor proteins
Bacteriophages genomes are typically composed of
double-stranded DNA
The use of ________ is the easiest and most effective way of studying many animal and plant viruses
tissue or cell culture
The life cycle of lambda phage is controlled by accumulation of repressor proteins. For lysogeny to occur
cl protein predominates
Viral proteins are categorized as early, middle, and late. Early proteins typically are necessary for
production of viral mRNA and copying the viral gene
Which of the following are the hosts for most enveloped viruses?
animals
For bacteriophages and animal viruses ______ is the step in the viral life cycle that determines host cell specificity.
attachment
Some bacteriophage possess an enzyme similar to _______, which makes a small hole in the bacterial cell wall, allowing the viral nucleic acid to enter
lysozyme
How are viruses different from cells?
they require a host in order to reproduce
What is the function of the structural elements of a virus?
to package and protect the viral genome
T4 genes are transcribed by host RNA polymerase, yet this transcription is carefully controlled so that groups of T4 genes are transcribed in a specific order after infection. How is this accomplished?
Early and middle T4 genes encode for RNA polymerase-modifying proteins so that only phage promoters are recognized.
Which of the following examples is an example of lysogenic conversion?
Vibrio cholerae bacteria produce cholera toxin when infected with a phage.
Which of the following groups contains some representatives with genomes that are so small that they may have as few as two genes?
RNA viruse
What is the benefit for a bacteriophage to be a temperate (or lysogenic) virus?
A single infection event can produce millions of new viral particles instead of hundreds of viral particles
How is penetration different in animal viruses as compared to bacterial viruses?
The entire viral particle can penetrate an animal cell, while only the viral genome can penetrate a bacterial cell.
Prokaryotic restriction endonucleases are effective at destroying a virus whose genome consists of
ds DNA
The packaging mechanism of T4 DNA involves cutting of DNA from
DNA concatemers
Plaque assays are often used to estimate the number of virions in a sample of a particular volume (the titer). The count is given as plaque-forming units. Which of the following is NOT generally a concern that must be considered in evaluating the results of plaque assays?
The largest problem is that single viruses may create multiple plaques, resulting in overestimates of the number of viruses present.
Lysogenic viral DNA integrating into the host genome is referred to as
a prophage
Which of the following events might trigger induction of a temperate bacteriophage?
exposure to UV light
How is the lytic cycle different from the lysogenic cycle with respect to the infected host cells?
The host cell dies during the lytic stage
What is the fate of the prophage during the lysogenic stage?
It is copied everytime the host DNA replicates
The concentration of infectious plaque forming units (pfu) per volume of fluid is known as the
titer.
The majority of many important human viral diseases are caused by
ssRNA viruses
When determine the number of virus particles in a suspension, why is the number obtained always less than the actual viral titer?
because all of the virus particles do not infect with 100% efficiency
A retrovirus has a genome that consists of _________.
ssRNA
Viruses infecting _______ are typically the easiest to grow in the laboratory.
prokaryotes
A cell that allows the complete replication cycle of a virus to take place is said to be
permissive host
The T4 bacteriphage could not infect Staphylococcus auereus because this bacterium does NOT posesses a
lipopolysaccharide outer membrane
All viral particles
are metabolically inert
Viral replication is
independent of the host cell's DNA but dependent on the host cell's enzymes and metabolism
What component(s) make up the structure of a virion?
capsid and genome
Why does the structure of plant and bacterial cells illustrate the reason for having few enveloped viruses that infect these cells?
Plant and bacterial cells contain cell walls that limit the virus from budding out and obtaining the envelope
Reverse transcriptase is a(n)
RNA-dependent DNA polymerase
When packaged in the virion, the complete complex of nucleic acid and protein is known as the virus
nucleocapsid
Which of the following are viable methods of release of newly assembled viral particles?
budding or lysis of host cell
When a solution composed of bacteria and infectious virions are mixed and spread on an agar plate, _____ form where viruses lyse the host cells.
plaques