Deck 8: Viruses and Their Replication

Question 1

Which statement is TRUE?

A) All viruses contain their own nucleic acid polymerases.
B) RNA viruses contain their own nucleic acid polymerases.
C) Viruses do not contain their own nucleic acid polymerases.
D) The origins of the nucleic acid polymerases used by viruses are eukaryotic.

Answer 1

B

Question 2

Which of the following enzymes would you expect to find in the virion of a retrovirus, but NOT in a bacteriophage?

A) lysozyme
B) methylase
C) restriction enzymes
D) reverse transcriptase

Answer 2

D

Question 3

Viral size is generally measured in

A) micrometers.
B) picometers.
C) nanometers.
D) centimeters.

Answer 3

C

Question 4

Viruses infecting ________ are typically the easiest to grow in the laboratory.

A) plants
B) animals
C) fungi
D) prokaryotes

Question 5

A prophage replicates

A) along with its host while the lytic genes are expressed.
B) along with its host while the lytic genes are not expressed.
C) independently of its host while the lytic genes are expressed.
D) independently of its host while the lytic genes are not expressed.

Question 6

Enveloped viral membranes are generally ________ with associated virus-specific ________.

A) lipid bilayers / phospholipids
B) protein bilayers / lipids
C) lipid bilayers / proteins
D) glycolipid bilayers / phospholipids

Question 7

Bacteriophagesʹ genomes are typically composed of

A) single-stranded RNA.
B) single-stranded DNA.
C) double-stranded RNA.
D) double-stranded DNA.

Question 8

Viral replication is

A) independent of the host cell's DNA but dependent on the host cell's enzymes and metabolism.
B) independent of both the host cell's DNA and the host cell's enzymes and metabolism.
C) dependent on the host cell's DNA and RNA.
D) dependent on the host cell's DNA, RNA, enzymes, and metabolism.

Question 9

Restriction is

A) the viral process whereby a hostʹs DNA ceases normal functioning.
B) the viral process whereby the virus prevents other viruses from entering the cell.
C) a general host mechanism to prevent the invasion of foreign nucleic acid.
D) a general host mechanism to prevent virus particles from further infective action.

Question 10

The life cycle of lambda phage is controlled by accumulation of repressor proteins. For lysogeny to occur

A) cI protein predominates.
B) Cro protein predominates.
C) cII protein is repressed.
D) cI protein is repressed.

Question 11

Retroviruses are medically important viruses because

A) they include the poliovirus.
B) they include the influenza virus.
C) they include all human pathogenic viruses.
D) they include some viruses that cause cancer and HIV.

Question 12

Which of the following statements is FALSE?

A) Lambda is a temperate phage that infects Escherichia coli.
B) Lambda is a linear double-stranded DNA phage.
C) Lambda is replicated by the rolling circle mechanism.
D) Lambda always circularizes upon entering the host cell.

Question 13

All of the following can act as receptors for various bacteriophages EXCEPT

A) iron transport proteins.
B) flagella.
C) Sugar transporters.
D) cilia.

Question 14

Reverse transcriptase is a(n)

A) RNA-dependent DNA polymerase.
B) DNA-dependent DNA polymerase.
C) RNA-dependent RNA polymerase.
D) DNA-dependent RNA polymerase.

Question 15

Viral replication occurs

A) intracellularly.
B) extracellularly.
C) both intracellularly and extracellularly.
D) either intracellularly or extracellularly, depending on the virus involved.

Question 16

A virus that kills its host is said to be

A) lytic or virulent.
B) temperate.
C) lysogenic.
D) virulent or lysogenic, but not temperate.

Question 17

The packaging mechanism of T4 DNA involves cutting of DNA from

A) linear genetic elements.
B) circular genetic elements.
C) DNA concatemers.
D) its host cells.

Question 18

Cellular receptors may be composed of

A) proteins.
B) carbohydrates.
C) lipids.
D) combinations of proteins, carbohydrates, and/or lipids.

Question 19

all viral particles

A) are metabolically inert.
B) are smaller than bacterial cells.
C) contain an envelope to prevent its degradation outside of a host.
D) exhibit cell lysis under a particular condition.

Question 20

The T4 bacteriophage could not infect Staphylococcus aureus because this bacterium does NOT possess a

A) lipopolysaccharide outer membrane.
B) teichoic acid outer membrane.
C) pili.
D) flagella.

Question 21

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?

A) deletion or inactivation of the cI gene
B) deletion or inactivation of the cro gene
C) overexpression of the cro gene
D) deletion of both the cro and cI genes

Question 22

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?

A) Early T4 genes encode for proteolytic enzymes that destroy the host RNA polymerase. Subsequently a viral polymerase is created that transcribes the middle and late genes in the correct order.
B) Early and middle T4 genes encode for RNA polymerase-modifying proteins so that only phage promoters are recognized.
C) Each group of T4 genes has a different promoter that indicates the order in which they should be transcribed based on the affinity of the promoter for the host RNA polymerase.
D) Rolling circle replication of the viral genome ensures that the genes are available for transcription in the correct order.

Question 23

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?

A) The enzymes cut the E. coli genome into pieces that bind to viral particles and inhibit viral replication.
B) The enzymes increase the rate of mutation and genome rearrangement, thus increasing the likelihood that E. coli cells will mutate and become resistant to viral infection.
C) The enzymes encourage lysogeny because the cleavage sites are recognized by viral integrases.
D) The enzymes protect E. coli from infection by preferentially degrading viral or other exogenous DNA that is not methylated.

Question 24

Which of the following are the hosts for most enveloped viruses?

A) Bacteria
B) animals
C) Archaea
D) fungi

Question 25

The use of ________ is the easiest and most effective way of studying many animal and plant viruses.

A) bacterial cultures
B) tissue or cell culture
C) live hosts
D) prophages

Question 26

The majority of many important human viral diseases are caused by

A) ssRNA viruses.
B) ds RNA viruses.
C) ss DNA viruses.
D) ds DNA viruses.

Question 27

The term ʺphageʺ is generally reserved for the viruses that infect

A) animals.
B) plants.
C) bacteria.
D) multiple species.

Question 28

The genome of retroviruses contains genes to make all of the following EXCEPT

A) structural proteins.
B) repressor proteins.
C) integrase.
D) proteases.

Question 29

The T4 phage protects its DNA from host restriction endonucleases by

A) glucosylating cytosine bases in the T4 genome to prevent DNA cleavage.
B) methylating all four bases (A, T, C,
C) integrating the viral genome into the host genome where it will not be degraded.
D) circularizing the viral genome so that it will not be degraded.
G) in the T4 genome to prevent DNA cleavage.

Question 30

When a virus enters a host cell in which it can replicate, the process is called a(n)

A) insertion.
B) infection.
C) prophage.
D) excision.

Question 31

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.

Question 32

Rolling circle replication of the lambda genome differs from replication of a bacterial chromosome in that

A) bidirectional replication forks are not formed.
B) only a single strand of the genome is copied.
C) no concatamers are formed.
D) only a single strand of the genome is copied and no concatamers are formed.

Question 33

Viral proteins are categorized as early, middle, and late. Early proteins typically are necessary for

A) production of viral mRNA.
B) packaging of DNA into the nucleocapsid.
C) copying the viral genome.
D) production of viral mRNA and copying the viral genome.

Question 34

When packaged in the virion, the complete complex of nucleic acid and protein is known as the virus

A) capsid.
B) concatemer.
C) nucleocapsid.
D) envelope.

Question 35

As a consequence of infection by a temperate bacteriophage such as lambda, the host cell

A) lyses as a result of bacteriophage release.
B) never lyses but continues to divide and replicate both itself and the prophage.
C) divides faster at moderate temperatures.
D) may lyse or may continue to divide and replicate both itself and the prophage.

Question 36

The size and shape of viral particles is largely governed by the size and packaging of the viral

A) envelope.
B) enzymes.
C) prophage.
D) genome.

Question 37

Regarding the viral membrane of an enveloped virus, the lipids are derived from the ________, and the proteins are encoded by ________.

A) hostʹs cell membrane / viral genes
B) virion / viral genes
C) hostʹs cell membrane / hostʹs genes
D) virion / hostʹs genes

Question 38

The HIV genome consists of

A) a single ds RNA molecule.
B) two identical ssRNA molecules.
C) two identical ssDNA molecules.
D) a single DNA molecule.

Question 39

Some bacteriophage possess an enzyme similar to ________, which makes a small hole in the bacterial cell wall, allowing the viral nucleic acid to enter.

A) peptidoglycanase
B) infectase
C) lysozyme
D) nuclease

Question 40

When a solution composed of bacteria and infectious virions are mixed and spread on an agar plate, ________ form where viruses lyse the host cells.

A) insertion sequences
B) plaques
C) prophages
D) colonies

Question 41

Viruses can confer additional properties on their host cells, which can in turn be inherited.

Question 42

Budding of virions from an infected host results in enveloped virus.

Question 43

Penetration requires that the entire virus is inserted within the host.

Question 44

What would be the consequence of deleting the late T4 genes?

A) The T4 genome would not be copied.
B) T4 mRNA would not be produced.
C) T4 capsid proteins would not be made.
D) ATP would not be produced and the T4 genome would not be packaged into the capsid.

Question 45

For bacteriophages and animal viruses ________ is the step in the viral life cycle that determines host cell specificity.

A) attachment
B) penetration
C) synthesis
D) assembly

Question 46

For a virus to cause a latent infection, it must possess

A) ssDNA.
B) ds DNA.
C) dsRNA.
D) Any type of viral genome can lead to a latent infection.

Question 47

What are the possible consequences of viral infection of an animal cell?

A) rapid lysis or latent infections
B) lysogeny followed by eventual lysis
C) lysis or lysogeny
D) Outcomes vary from rapid lysis to persistent infections, latent infections, or cancer.

Question 48

In a natural population of diverse slow-growing prokaryotic cells, what type of viruses would you expect to be most common?

A) lytic bacteriophages
B) enveloped viruses
C) icosahedral viruses
D) temperate bacteriophages

Question 49

The genome of a temperate phage can replicate along with the host genome during lysogeny.

Question 50

In a population of T4 virus, each virion has the same set of genes, but they are arranged in a different order.

Question 51

The general steps of the viral lifecycle are similar in most viruses. One major exception, however, is entry into the host cell. How does this step differ between an animal cell and E coli?

A) The entire virion is taken into an animal cell, but only the viral genome enters E coli.
B) The entire virion enters E coli, but only the nucleic acid is taken up by animal cells.
C) The virion fuses to the bacterial cell membrane of E coli, while the genome is injected into an animal cell.
D) The virion randomly attaches to E coli, but viral binding to a specific receptor is required for entry into animal cells.

Question 52

Accumulation of the cI protein results in integration of the lambda genome and prophage formation.

Question 53

A cell that allows the complete replication cycle of a virus to take place is said to be a

A) permissive host.
B) viral cell.
C) dead cell.
D) lytic cell.

Question 54

RNA viruses encode host restriction systems designed to destroy host DNA.

Question 55

The concentration of infectious plaque forming units (pfu) per volume of fluid is known as the

A) infectivity.
B) virulence.
C) titer.
D) fluid infectivity.

Question 56

The growth of viruses in a culture is described as a one-step growth curve, because

A) virion numbers show no increase during intracellular replication and can only be counted after the virions burst from the host cell.
B) there is only one step in the viral life cycle which leads to only one replicative cycle in a culture.
C) assembly and release actually occur in one step.
D) the eclipse phase prevents the plating and enumeration of virions although new virions are produced at a steady rate during the eclipse phase.

Question 57

Prokaryotic restriction endonucleases are effective at destroying a virus whose genome consists of

A) ds DNA.
B) ssDNA.
C) dsRNA.
D) ssRNA.

Question 58

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?

A) The viral genome is ssRNA of the plus sense.
B) The viral genome is ssRNA of the minus sense.
C) The bacteriophage is a retrovirus.
D) The bacteriophage is probably a new strain and should be studied further.

Question 59

Virus assembly requires host cell mediated reactions.

Question 60

Rod-shaped viruses have icosahedral symmetry while spherical viruses have helical symmetry.

Question 61

Temperate viruses can enter into either a lytic or lysogenic cycle.

Question 62

In prokaryotes, DNA viruses replicate their genomes in the nucleus while RNA viruses are replicated in the cytoplasm.

Question 63

An RNA genome itself serves as mRNA in negative-stranded RNA viruses.

Question 64

Why have the majority of viruses evolved to bind to a host surface receptor that serves an essential function in the host cell?

Question 65

Lysogeny is unique to bacteriophages; similar relationships have not been found among the animal viruses.

Question 66

Relate the structure of bacteriophages and animal viruses to the structure of their respective host cells and the steps of the viral life cycle.

Question 67

Although T4 encodes over 250 proteins, it does not encode its own RNA polymerase.

Question 68

Influenza is an acute human viral disease that causes brief cellular damage followed by healing and complete clearing of the virus from the body. Hepatitis C is a chronic viral disease that causes slow destruction of liver tissue and persistent virions that are not completely cleared. Which of these diseases is more likely to be caused by lytic virus and which is caused by a non-lytic virus?

Question 69

The reason dogs do not get measles is because their cells lack the correct receptor sites for that virus.

Question 70

T4 and other bacteriophages commonly use a method of DNA replication and packaging called ʺheadful packaging.ʺ Explain how viral genomes are replicated and packaged in this process and hypothesize how headful packaging might affect evolution of BOTH the bacteriophages and their prokaryotic hosts.

Question 71

Compare and contrast the structure, life cycle, and host cell type of naked and enveloped viruses.

Question 72

Explain the potential advantages of lysogeny versus lysis for a temperate virus.

Question 73

The genome of a retrovirus consists of dsRNA.

Question 74

Describe the establishment and maintenance of the lysogenic state in the lambda phage.

Question 75

Why was the discovery of retroviruses important to the field of molecular biology?

Question 76

Explain why viruses are not considered to be living entities.

Question 77

The latent phase in the viral growth curve and the lag phase of the bacterial growth curve are equivalent and represent the time it takes for the virus or bacterium to adapt to the culture conditions and begin growing.

Question 78

A lytic infection results in death of the host cell.

Question 79

How does plating efficiency affect the number of plaque-forming units? How is plating efficiency calculated?

Question 80

A naked virus lacks a capsid.