Microbiology- Chapter 11
The Baltimore classification scheme is a useful way to categorize viruses based on their host infectivity.
false
To date, there is no evidence that RNA viruses infect Archaea.
false
Varied transcription mechanisms distinguish the different DNA virus Baltimore classes, whereas varied translational mechanisms distinguish RNA viruses.
false
Viruses are known to infect Bacteria, but no virus has yet been found that infects Archaea
false
Viruses that contain positive-strands genomes do not share genetic elements with positive-strand genomes
false
The T4 phage protects its DNA from host restriction endonuclease by
glucosylating cytosine bases in the T4 genome to prevent DnA cleavage
Polyproteins made from human viruses such as poliovirus must be ________ in order to yield the required functional units of the virus.
post-translationally cleaved
The genome of retroviruses contains genes to make all of the following EXCEPT
repressor proteins
A drug designed to inhibit reverse transcriptase activity would target
retroviruses
The Baltimore Scheme to classify viruses contain a total of ______ groups based on _____.
seven/ genome composition and transcription mechanism
Herpes viruses can cause all of the following diseases in humans EXCEPT
spongiform encephalopathy
Which feature, if changed, would NOT abolish M13's utility as a cloning vector?
ssDNA genome becoming a dsDNA genome
Proteins made by a ribosome reading through the stop codon of a transcript without their own discrete ribosome binding sites
suggest a relatively low level of protein product is essential for the virus due to the rare frequency of these events
Prophage formation occurs after lambda infection if A) the cI gene is transcribed and cI protein accumulates. B) cII expression occurs. C) Cro accumulates in the cell. D) both Cro and cI are equally activated.
the cI gene is transcribed and cI protein accumulates
In E. coli, the adenine in the sequence GATC is methylated by the Dam enzyme. In the same cells, a restriction endonuclease recognizes and cleaves dsDNA with the sequence GATC on either strand. Why does E. coli have these two enzymes?
the enzymes protects E. coli from infection by preferentially degrading viral or other exogenous DNA that is not methlated
As a consequence of the immune system in humans recognizing dsRNA as foreign
the genomes of dsRNA viruses must avoid human immune cells during infection, including replicating their genomes within their own nucleocapsids.
Early and late viral proteins are classified according to their relative
time of synthesis following host infection
Despite viruses require a living host's metabolism to replicate, it remains unclear whether viruses existed before living cells.
true
Genomics analysis of recently isolated viruses indicate some viruses contain larger genomes than the some bacterial genomes.
true
One hypothesis on the origin of DNA points to RNA viruses evolving a modified nucleotide that is insensitive to ribonucleases
true
The HIV genome consists of
two identical ssRNA molecules.
Spindle-shaped viruses have been shown to infect only
Archaea
Unusually shaped viruses, such as lemon-shaped and spindle-shaped, have recently been discovered in
Archaea
Due to the genetic diversity of viruses and their lack of ribosomal RNA, nucleotide-based phylogeny studies are not applicable to virology
False
In prokaryotes, DNA viruses replicate their genomes in the nucleus while RNA viruses are replicated in the cytoplasm
False
Nonfilamentous bacteriophages often can escape a host without lysing, whereas filamentous phages normally induce cell lysis once replicated inside a host.
False
Viroids infect only fungi
False
Based on its function, which type(s) of viruses likely contain(s) a gene encoding for RNA replicase?
Positive and negative ssRNA viruses
Which type of viruses can be directly used for translation?
Positive ssRNA
Accumulation of the cI protein results in integration of the lambda genome and prophage formation.
True
By nature of its infectivity, M13 phage can be used in the laboratory to continually propagate a particular DNA sequence inside of Escherichia coli by simply culturing infected E. coli in LB.
True
Due to their indispensable role for copying its genome, an intracellular host protease that attacks the adenoviral protein ends would likely result in halting its replication.
True
In order to replicate its genome, a positive-strand RNA virus must produce a complete negative-strand RNA molecule that serves as the template for protein synthesis.
True
Many viruses that infect humans may illicit a strong immune response causing additional harmful effects, so the discovery of a virus that can induce an immune response without causing harm made it attractive for vaccine development.
True
Most archaea viruses identified appear to have DNA genomes
True
Some virus shapes that infect members of Archaea are unique from other viruses that infect eukaryotes and bacteria.
True
Which of the following conditions favors a lysogenic life cycle in bacteriophages?
a lack of host bacteria
Bacteriophages that have single-stranded genomes are specialized to minimize energy requirements because just one strand is necessary for replication.
False
The unconventional dsDNA genome replication mechanism where no lagging strand exists is a hallmark of which group of viruses?
Adenovirus
The hepadnaviral DNA polymerase acts as which of the following?
DNA polymerase, reverse transcriptase, and protein primer for DNA synthesis
How could overlapping genes in a positive ssDNA virus genome be predicted?
Directly search the three frames of the positive ssDNA for genes that have sequences where more than one gene is predicted
A bacteriophage that lacks its proteinaceous capsid structure is also called a viroid
False
An RNA genome itself serves as mRNA in negative-stranded RNA viruses.
False
What is unusual about phage MS2 infection of Escherichia Coli?
It attaches to the host's pilus rather than the cell's surface
If the hypothesis stating viruses evolved prior to living organisms on Earth is true, the first type of viruses in the world were likely
RNA viruses
Which type of viruses generally has the smallest genome?
RNA viruses
Of the phages listed below, which contains a double-stranded DNA genome composed of early and late genes
T7
How are T7 genes transcribed?
T7 has its own RNA polymerase, which must first be synthesized by the host.
You isolate a bacteriophage that can replicate in E. coli. Through chemical analyses you determine that the only nucleic acid present is RNA. You isolate the RNA and put it in a test tube with all of the enzymes, amino acids, and RNAs necessary for translation. The RNA is translated directly, without being copied into a complementary strand first, and new infectious virions are made and released. What does this tell you about the bacteriophage?
The viral genome is ssRNA of the plus sense
How do reoviruses increase the translational activity of human ribosomes so that they can rapidly produce viral proteins during infection? A) They chemically modify the RNA transcripts with methyl caps in a similar manner to normal eukaryotic RNA processing. B) They keep a ribosome binding site specific to human ribosomes on their genome. C) They have introns and sometimes extons in their genomes to make their RNA resemble eukaryotic mRNA. D) They only adhere to and infect metabolically active host cells where protein synthesis is high.
They chemically modify the RNA transcripts with methyl caps in a similar manner to normal eukaryotic RNA processing
What is the purpose of synthesizing a negative strand of RNA in a positive ssRNA virus?
To serve as the complementary template sequence in genome amplification of the positive strand
The _____ has been especially useful for genetic engineering because it is capable of triggering a substantial immune response without causing major adverse health effects.
Vaccinia virus
When two different influenza viruses infect the same cell, their segmented genomes can undergo reassortment which will result in
antigenic shift
The filamentous DNA phages are unusual, because they
are released from the host without the host being lysed
Blocking polyomavirus SV40's ability to integrate its genome into host cells would
avoid cancer development caused by the virus
In T7, the proteins that inhibit the host restriction system are synthesized
before the entire T7 genome enter the cell
Rolling circle replication of the lambda genome differs from replication of a bacterial chromosome in that
bidirectional replication forks are not form
A concatemer is a
combination of two or more repeated nucleotide sequences covalently linked together
The family of reoviruses contain dsRNA genomes use a ________ replication process. A) conservative B) semiconservative C) retroviral D) rolling circle
conservative
Identifying that protease are essential for the replication of a virus would suggest that the virus
contains at least one polyprotein
Among the largest RNA genome viruses are ________ which contain a ________ genome.
coronaviruses/ positive ssRNA
In designing a drug to inhibit pox viruses, the compound should localize in the host's ________ to be MOST effective.
cytoplasm
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
Mu is a(n) _____ virus
dsDNA
Prokaryotic restriction endonucleases are effective at destroying a virus whose genome consists of
dsDNA
Viruses that infect the hyperthermophilic Archaea tend to contain genomes that are composed of
dsDNA
Reoviruses contain ________ genomes, and their replication occurs within the host's ________.
dsRNA/ cytoplasm
In contrast to positive ssRNA viruses such as coronaviruses and polioviruses, the genome of retroviruses
must first integrate into the host's genome before transcription