Chapter 13: Viruses, Viroids, and Prions

Bacteriophage

(phage) A virus that infects bacteria.

Lysogen

A bacterium that carries phage DNA (the prophage) integrated into its genome.

Lysogenic Conversion

A change in the properties of a bacterium conferred by a prophage.

Virion

A complete virus in its inert non-replicating form; also referred to as a viral particle.

What is the difference between a viroid and a prion?

A viroid is infection RNA and a prion is infectious protein.

The term "filterable viruses" was coined by A. Beijerinck B. Iwanowsky C. Twort D. d'Herelle

A. Beijerink

Which is a filamentous phage? A. M13 B. T4 C. lambda D. phi X174

A. M13

The family to which the Rhinovirus belongs is the A. Picornaviridae B. Enterobirus C. Enteroviridae D. Picornavirus

A. Picornaviridae

Genetic exchange is segmented viruses that allows a zoonotic virus to infect humans is termed A. antigenic shift. B. hemagglutination. C. genetic reassortment. D. antigenic drift.

A. antigenic shift.

The tail fibers on phages are associated with A. attachment. B. penetration. C. transcription of phage DNA. D. assembly of virus. E. lysis of host.

A. attachment.

The changes that occur in virally-infected cells are characteristic for a particular virus and are referred to as the A. cytopathic effect. B. phenotypic effect. C. genotpic expression. D. cytology.

A. cytopathic effect.

The replicative form of nucleic acid in filamentous phages is A. dsDNA B. dsRNA C. positive ssRNA D. negative ssDNA

A. dsDNA

The integration of phage DNA into the bacterial chromosome occurs because of A. identical DNA sequences in both. B. the phage's ability to synthesize enzymes to enter the bacterium. C. similar RNA nucleotides in both. D. the similarity in enzyme metabolism. E. B and C

A. identical DNA sequences in both.

Phages that can either replicate and cause cell lysis or can integrate their DNA into the host DNA are called A. lysogenic phages. B. lytic phages. C. virulent phages. D. segmented phages.

A. lysogenic phages.

The term "segmented" refers to viruses that A. may contain several pieces of RNA. B. have an icosahedral-shaped capsid. C. are linked together before budding out. D. have an envelope.

A. may contain several pieces of RNA.

Filamentous phage A. only infect E. coli that have pili. B. only infect E. coli lacking pili. C. infect E. coli regardless of the presence of pili. D. do not infect E. coli.

A. only infect E. coli that have pili.

Quantitating viral titers of both phage and animal viruses frequently involves A. plaque formation. B. quantal assays. C. hamagglutination. D. determining the ID50. E. counting of virions by microscopy.

A. plaque formation.

The approximate viral concentration of a sample may be determined by A. quantal assay. B. endpoint assay. C. the titer. D. the lysate assay.

A. quantal assay.

The filamentous phages all contain A. single-stranded DNA. B. double-stranded DNA. C. single-stranded RNA. D. double-stranded RNA.

A. single-stranded DNA.

Viroids characteristically are composed of A. ssRNA B. dsRNA C. ssDNA D. dsDNA

A. ssRNA

In the replication of phage containing positive-sense DNA, A. the host's enzymes are used to make dsDNA. B. the host's DNA polymerase uses the phage RNA as a template to make negative-sense DNA. C. a phage-encoded DNA polymerase is used to make negative-sense RNA using the phage positive-sense RNA as a template. D. a phage-encoded DNA polymerase is used to make DNA using the phage positive-sense RNA as a template.

A. the host's enzymes are used to make dsDNA.

After growth in tissue culture, the infected cells lyse and the virus may be harvested from A. the liquid supernatant after centrifugation, the lysate. B. the remainder. C. the quantal layer. D. the monolayer.

A. the liquid supernatant after centrifugation, the lysate.

A phage that replicates inside the host cell and then lyses its host during its release is a A. virulent or lytic phage. B. latent phage. C. lysogenic phage. D. dormant phage.

A. virulent or lytic phage.

Plant viruses enter the host plant via A. wound sites. B. specific receptors. C. nonspecific receptors. D. seeds.

A. wound sites.

Viroid

An infectious agent of plants that consists only of RNA.

Prion

An infectious agent that causes a neurodegenerative disease; consists of protein similar in amino acid sequence to a normal protein in the body.

Animal viruses are divided into a number of families whose names end in A. -virus B. -viridae C. -viscous D. -eieio

B. - viridae

What is a defective phage? A. A virus that has lost some of its genetic material and therefore cannot infect a new target cell. B. A virus that has lost some of its genetic material, and therefore cannot replicate within a new target cell. C. A virus that lacks the ability to replicate independently of its host cell. D. A virus that cannot attach to its host cell.

B. A virus that has lost some of its genetic material, and therefore cannot replicate within a new target cell.

The nucleocapsid is composed of A. DNA and RNA and protein. B. DNA or RNA and protein. C. protein located in the nucleus. D. nucleic acid in the ribosome.

B. DNA or RNA and protein.

What part of the E. coli T4 phage attaches to the host cell receptors? A. Capsid fragments around the nucleic acid B. Protein fibers at the end of the phage tail C. Pili of the envelope D. Spikes of the envelope

B. Protein fibers at the end of the phage tail

Crystallization of Tobacco Mosaic Virus was accomplished by A. Berkley B. Stanley C. Iwanowsky D. Twort

B. Stanley

One of the most intensively studied virulent phages which infects E. coli is A. T9. B. T4. C. beta. D. gamma.

B. T4.

Which of the following is not a characteristic of normal cells? A. The grow as a monolayer. B. They grow as multiple layers. C. They undergo a limited number of divisions and then die. D. They stick tightly to the surface of glass culture dishes.

B. They grow as multiple layers.

Prions A. consist of a special nucleocapsid. B. are made of protein only. C. are made of RNA only. D. are made of dsRNA and protein.

B. are made of protein only.

The correct order for the stages of phage infection is: A. penetration, transcription, attachment, replication of nucleic acid and protein, assembly, release B. attachment, penetration, transcription, replication of nucleic acid and protein, assembly, release C. attachment, replication of nucleic acid and protein, penetration, transcription, assembly, release D. transcription, attachment, replication of nucleic acid and protein, assembly, penetration, release

B. attachment, penetration, transcription, replication of nucleic acid and protein, assembly, release

Transducing virulent phages do not lyse the cells they invade because A. transformation is taking place in the phage and this is transferred to the bacterium. B. bacterial DNA has replaced critical viral DNA in the phage. C. their virulence is dependent on the bacteria and virus replicating together. D. the lytic genes are unable to enter during penetration and are shed outside the host.

B. bacterial DNA has replaced critical viral DNA in the phage.

In addition to lysis, animal viruses may exit the host cell by A. extrusion B. budding C. fission D. fusion

B. budding

The shape of the virus is determined by its A. nucleic acid B. capsid C. envelope D. tail

B. capsid

Enveloped viruses A. just require a stamp. B. have an outer lipid bilayer membrane containing various proteins. C. are surrounded by an additional layer of carbohydrate. D. envelope a cell.

B. have an outer lipid bilayer membrane containing various proteins.

Using phages to treat a bacterial infection is an interesting idea because A. a single type of phage can destroy a wide range of strains of the same pathogen. B. of the increasing problem of antibiotic resistance. C. lysed bacteria pose no threat. D. a single phage can be genetically engineered to infect many different species of bacteria.

B. of the increasing problem of antibiotic resistance.

In latent infections, the virions are A. constantly produced. B. only produced during reactivation. C. produced slowly. D. continually being slowly budded out.

B. only produced during reactivation.

Viroids cause disease in A. animals B. plants C. bacteria D. fungus

B. plants

During penetration of E. coli by the T4 phage A. lysozyme is used to allow entry of the phage capsid. B. the tail acts as a "hypodermic needle", injecting the phage DNA into the cell. C. the protein fibers digest a hole in the cell wall. D. the bacterial receptor molecules open a hole through the cell wall.

B. the tail acts as a "hypodermic needle", injecting the phage DNA into the cell.

In the case of T-even phages, the burst size is about A. 2 per host cell. B. 5 per host cell. C. 200 per host cell. D. 1000 per host cell.

C. 200 per host cell.

The time from absorption to release for T-even phage is about A. 1 minute. B. 10 minutes. C. 30 minutes. D. 1 day.

C. 30 minutes.

The site at which a virus has infected and subsequently lysed the infected cell, releasing its progeny to infect and lyse surrounding cells, thereby forming a "clear zone", is referred to as A. a burst area. B. a lyse area. C. a plaque. D. a dead zone.

C. a plaque.

Diseases of short duration frequently followed by long-term immunity are referred to as A. intermittent infections. B. chronic infections. C. acute infections. D. persistent infections.

C. acute infections.

Filamentous phages A. infect animal and bacterial cells. B. cause their host cells to grow more quickly. C. are extruded from the host cell. D. undergo assembly in the cytoplasm. E. degrade the host cells' DNA.

C. are extruded from the host cell.

Once integrated, phage DNA can remain in the prophage state as long as A. the bacteria is frequently plated on new media. B. certain phage genes are excised. C. certain phage genes are repressed. D. bacterial repressor genes are activated.

C. certain phage genes are repressed.

A virion is a(n) A. pathogenic virus. B. subviral particle. C. complete, extracellular virus particle. D. enveloped virus particle.

C. complete, extracellular virus particle.

If the infecting phage lacks some critical pieces of DNA necessary for replication it is called A. incomplete. B. mutated. C. defective. D. vegetative.

C. defective.

The common species name of the virus is based on the A. presence or absence of a nuclear membrane. B. type of nucleic acid it contains. C. disease the virus causes. D. geographic area it was found.

C. disease the virus causes.

The viral envelope closely resembles the A. prokaryotic cell wall. B. capsomere. C. eukaryotic cell membrane. D. cytoplasm.

C. eukaryotic cell membrane.

An exit method used by viruses which does not immediately destroy the host bacterium is A. lysis B. inversion C. extrusion D. excising

C. extrusion

The bacterial viruses that are released by a process termed extrusion are called A. lysogenic viruses B. temperate phages C. filamentous phages D. lambda viruses

C. filamentous phages

Cells infected with animal viruses lyse because A. the release of the virions depletes the cell of energy. B. the virus releases enzymes that lyse the cell. C. functions necessary for cell survival are not carried out and the cell dies. D. the virus RNA and cellular protein interact to kill the cell.

C. functions necessary for cell survival are not carried out and the cell dies.

DNA is protected from restriction enzymes by being A. sequestered in a lysosome. B. turned into RNA. C. methylated. D. made into double stranded RNA.

C. methylated.

Prions affect the A. respiratory system B. gastrointestinal tract C. nervous system D. lymphatic system

C. nervous system

Capsids are composed of A. DNA B. RNA C. protein D. lipids E. polysaccharides

C. protein

Classification of viruses is based on all of the following EXCEPT A. type of nucleic acid. B. shape of virus. C. size of virus. D. host infected. E. strandedness of nucleic acid.

C. size of virus.

RNA phages usually contain A. dsRNA B. dsDNA C. ssRNA D. ssDNA

C. ssRNA

The genome of retroviruses is made of A. ssDNA B. dsDNA C. ssRNA D. dsRNA

C. ssRNA

What part of the attached bacteriophage enters through the host cell wall? A. the entire virus B. only the enzymes necessary for replication C. the nucleic acid D. the nucleic acid and capsid E. the capsid only

C. the nucleic acid

Retroviruses are unique in that they A. replicate in nervous system cells. B. do not have a capsid. C. use RNA as a template to make DNA. D. use DNA as a template to make RNA.

C. use RNA as a template to make DNA.

Transmission of plant viruses by insects can occur from A. viruses associated with insect mouth parts. B. viruses circulating but not multiplying in the insect's body. C. viruses that multiply within the body of the insect. D. All of the above.

D. All of the above.

Most phages that contain single-stranded DNA A. are extruded. B. contain a positive-sense DNA strand. C. have their DNA transformed to double-stranded DNA before replication and transcription occur. D. All of the choices are correct.

D. All of the choices are correct.

Once inside the host cell, phage DNA A. is replicated. B. is transcribed. C. may get degraded by bacterial nucleases. D. All of the choices are correct.

D. All of the choices are correct.

Spongiform encephalopathy occurs in A. humans B. cattle C. sheep D. All of the choices are correct.

D. All of the choices are correct.

Regarding phage replication, A. the majority of the phages are temperate. B. when integrated into host DNA, the phage DNA is called a prophage. C. lambda is a good example of temperate phage. D. All the choices are correct.

D. All the choices are correct.

Prions are A. a form of RNA virus. B. a form of DNA virus. C. a viroid. D. an infectious protein.

D. an infectious protein.

Which does not refer to the shape of a virus? A. icosahedral (isometric) B. helical C. complex D. bacillus

D. bacillus

Viruses that infect bacteria are referred to as A. viralcidens B. bacteriocidins C. bacterialogens D. bacteriophages

D. bacteriophages

Viruses may not be cultivated in A. live organisms. B. embyonated chicken eggs. C. tissue culture. D. blood agar.

D. blood agar.

Temperate phages can do all of the following EXCEPT A. lyse their host cells. B. change properties of their hosts. C. integrate their DNA into the host DNA. D. bud from their host cells. E. become prophages.

D. bud from their host cells.

Bacteria infected with filamentous phages are termed A. temperate cells. B. plaque-producing cells. C. virulent strains. D. carrier cells.

D. carrier cells.

Prions A. contain only nucleic acid without a protein coat. B. replicate like HIV. C. integrate their nucleic acid into the host genome. D. cause diseases of humans. E. cause diseases of plants.

D. cause diseases of humans.

Bacteriophages and animal viruses A. both may enter a host cell by endocytosis. B. both may enter a host cell by fusion. C. both involve entry of the entire nucleocapsid D. differ because bacteriophages leave the capsid outside the cell, while animal virus entry involves the entry of the whole nucleocapsid.

D. differ because bacteriophages leave the capsid outside the cell, while animal virus entry involves the entry of the whole nucleocapsid.

If reasonably pure preparations of virus are available, the number of virus present may be determined by A. photocolorimetry. B. gas chromatography. C. light microscopy. D. electron microscopy.

D. electron microscopy.

When an enveloped virus adsorbs to the host cell with its protein spikes, the virions are taken into the cell by the process of A. penetration. B. production. C. fusion. D. endocytosis.

D. endocytosis.

What are two ways that phage can replicate in harmony (not direclty lysing) their host cell? A. conjugation and lysogeny B. lysogeny and transduction C. extrusion and transformation D. extrusion and lysogeny

D. extrusion and lysogeny

There are _____ families of RNA containing viruses that infect vertebrates. A. two B. five C. seven D. fourteen

D. fourteen

Influenza vaccines must be changed yearly because the amino acid sequence of the viral proteins change gradually over time. Based on this information, which is the most logical conclusion? The influenza virus... A. is enveloped. B. is naked. C. has a DNA genome. D. has an RNA genome. E. causes a persistent infection.

D. has an RNA genome.

The best known chronic infection involves A. chickenpox B. herpes C. hepatitis A D. hepatitis B

D. hepatitis B

Resistance of some animals to certain viral diseases is based on A. lack of spikes for attachment. B. phagocytosis of the virus by the host cell. C. the presence of the viral envelope. D. lack of specific receptors on the host cell.

D. lack of specific receptors on the host cell.

The phenomenon responsible for the ability of Corynebacterium diphtherium to produce the virulent toxin responsible for the devastating effects of diphtheria is called A. self-assembly. B. matrix conversion. C. prion protein. D. lysogenic conversion.

D. lysogenic conversion.

In the region of budding, the inside of the plasma membrane becomes coated with A. enzymes. B. carbohydrates. C. steroids. D. matrix proteins.

D. matrix proteins.

Outside of living cells, viruses are A. scavenging glucose. B. slowly stockpiling ATP from the mitochondria. C. using cilia to move to the next host. D. metabolically inert.

D. metabolically inert.

One group of animal viruses that are able to agglutinate red blood cells are the A. coronavirus B. retrovirus C. reovirus D. myxovirus

D. myxovirus

An infection in which the virus is continually present in the body is referred to as A. acute. B. balanced. C. determinant. D. persistent.

D. persistent.

A limiting factor for viral infection is A. internal metabolic temperature of the host cell. B. nutrition of the host cell. C. stage of cell cycle of the host cell. D. presence of specific receptor molecules on the host cell.

D. presence of specific receptor molecules on the host cell.

Normal tissue taken from animals and prepared immediately as media for viral growth is termed a(n) A. advantageous group. B. monolayer culture. C. plaque. D. primary culture.

D. primary culture.

A virion is composed of A. lipid, protein, and either RNA or DNA. B. protein and either RNA or DNA. C. protein and both, RNA and DNA. D. protein, either RNA or DNA, and possibly lipid.

D. protein, either RNA or DNA, and possibly lipid.

For which of the following processes are enzymes not required? A. replication B. translation C. maturation D. self-assembly

D. self-assembly

A key feature of all viral infections is the A. integration of viral DNA into host DNA. B. disintegration of host DNA. C. addition of a lipid membrane to the virus. D. separation of viral nucleic acid from the capsid.

D. separation of viral nucleic acid from the capsid.

There are _____ families of DNA containing viruses that infect vertebrates. A. two B. four C. five D. seven

D. seven

The terms isometric, icosahedral and pleomorphic refer to A. viral life cycles B. forms of nucleic acid. C. types of viral envelopes. D. shapes of viruses.

D. shapes of viruses.

The protein projections on the surface of a virus that are involved in attachment to the host cell are called A. suckers B. pili C. cilia D. spikes E. hooks.

D. spikes

Attachment of animal viruses to the host cell may be by means of A. a tail. B. the envelope. C. a capsid. D. spikes.

D. spikes.

The enveloped viruses typically obtain their envelope A. from the host plasma membrane. B. as they exit the host. C. from a newly constructed viral-derived membrane. D. from the nuclear membrane. E. A and B

E. (A and B) from the host plasma membrane AND as they exit the host.

Cells taken from a tumor A. may be used to grow viruses. B. can be cultivated in vitro indefinitely. C. may be used to grow bacteriophages. D. divide 50 times and then die. E. A and B

E. (A and B) may be used to grow viruses AND can be cultivated in vitro indefinitely.

Carriers A. may have a persistent infection. B. may be a source of infection. C. usually show symptoms of the disease. D. have been cured of the infection. E. A and B

E. (A and B) may have a persistent infection AND may be a source of infection.

Assembly of the T4 phage A. may involve some self-assembly. B. may involve the use of scaffolds. C. is completely self-assembly. D. is completely dependent on scaffolds. E. A and B

E. (A and B) may involve some self-assembly AND may involve the use of scaffolds.

The concentration of virus that infects or kills 50% of the host cells is referred to as the A. LD50 B. ID50 C. ID100 D. LD100 E. A and C

E. (A and C) LD50 and ID100.

A temperate phage A. may be lysogenic. B. may be lytic. C. enters a lysogenic or lytic life cycle shortly after entering the host cell. D. are all RNA viruses. E. A and C

E. (A and C) may be lysogenic AND enters a lysogenic or lytic life cycle shortly after entering the host cell.

Viruses A. probably keep the numbers of bacteria in check. B. have no effect on the number of bacteria. C. increase the number of bacteria. D. are active in passing DNA from one bacterium to another. E. A and D

E. (A and D) probably keep the numbers of bacteria in check AND are active in passing DNA from one bacterium to another.

Lysogenized cells A. are immune to any further infection by any virus. B. are immune to infection by the same virus. C. may have new properties. D. respond to infection with the SOS response. E. B and C

E. (B and C) are immune to infection by the same virus AND may have new properties.

During attachment of phage to E. coli, the phage A. actively seek out the bacteria. B. randomly bump into the bacteria. C. attach to proteins or carbohydrates on the bacterial surface. D. attach to the bacterial RNA. E. B and C

E. (B and C) randomly bump into the bacteria AND attach to proteins or carbohydrates on the bacterial surface.

In the region of budding, the plasma membrane becomes involved with A. carbohydrates. B. spike proteins. C. matrix proteins. D. enzymes. E. B and C

E. (B and C) spike proteins AND matrix proteins.

Phage-encoded proteins are A. coded for by host DNA. B. coded for by phage DNA. C. proteins normally present in the uninfected cell. D. early proteins. E. B and D

E. (B and D) coded for by phage DNA AND early proteins.

The activation of the SOS system in a bacterium infected with a prophage results in A. destruction of the viral genes. B. complete lysis of the bacterial culture. C. mutation of the DNA. D. destruction of the viral repressor through host protease activity. E. B and D

E. (B and D) complete lysis of the bacterial culture AND destruction of the viral repressor through host protease activity.

The best-known examples of viruses that cause latent infections are A. polio B. herpes C. measles D. chickenpox E. B and D

E. (B and D) herpes AND chickenpox

Phage-encoded enzymes are A. all produced simultaneously. B. produced in a sequential manner. C. strictly host enzymes. D. used to customize the cell for viral production. E. B and D

E. (B and D) produced in a sequential manner AND used to customize the cell for viral production.

Specialized transduction A. involves the random transmission of any gene. B. involves the transfer of a few specific genes. C. utilizes a defective virus. D. only involves genes near the viral DNA integration site. E. B, C and D.

E. (B, C and D) involves the transfer of a few specific genes, utilizes a defective virus, and only involves genes near the viral DNA integration site.

The protein coat of a virus A. is called a capsomere. B. is called a capsid. C. protects the nucleic acid. D. is involved in recognition of host cell receptors. E. B, C and D.

E. (B, C and D) is called a capsid, protects the nucleic acid AND is involved in recognition of host cell receptors.

Prions A. replicate by converting normal host proteins in prion proteins. B. responsible for "Mad Cow Disease" can cause a similar disease in humans. C. can be transmitted by consumption of dried or cooked food. D. that cause Spongiform Encephalopathy have the same amino acids but different folding properties from PrPc. E. All of the above.

E. All of the above.

Plant viruses may be transmitted by A. worms. B. contaminated seeds. C. humans. D. insects. E. All of the choices are correct.

E. All of the choices are correct.

Viruses are commonly referred to by their _____ name. A. locale B. genus C. disease D. species E. disease AND species

E. disease AND species

The receptors to which animal virus attachment proteins usually bind are A. proteins. B. carbohydrates. C. nucleic acid. D. lipids. E. glycoproteins.

E. glycoproteins.

(T/F) All single-stranded DNA phages are extruded.

False

(T/F) Bacteriophage, unlike animal viruses, often have special viral-specific enzymes carried in the capsid which enter the host cell at the same time as the nucleic acid.

False

(T/F) Capsids are made of a number of capsomeres which are covalently bonded to one another.

False

(T/F) Completed filamentous phages are often found in the cytoplasm of infected bacteria.

False

(T/F) Electron microscopy is useful for counting viruses and distiguishing between infective and non-infective virioins.

False

(T/F) Infective and non-infective viruses may be distinguished by growth on MacConkey's agar.

False

(T/F) The structure of plant, animal and bacterial viruses are each, fundamentally, very different from one another.

False

Plaque Assay

Method used to measure the number of viral particles present in a a sample.

What are restriction modification systems used for?

Prokaryotic defenses against viruses.

(T/F) A lysogenic cell contains viral DNA, a prophage, integrated into the host chromosome.

True

(T/F) All viruses must separate the nucleic acid from the capsid before replication.

True

(T/F) Filamentous virus is incapable of causing a lytic infection.

True

(T/F) If a virus utilizes a lytic life cycle of reproduction, it will not induce tumors.

True

(T/F) Naked and enveloped viruses both may enter the host via endocytosis.

True

(T/F) The RNA phages contain only a single positive-sense strand of RNA.

True

(T/F) The host range of a virus depends on the presence of host receptor molecules.

True

(T/F) The integration of phage DNA into host DNA occurs in much the same fashion as seen in transformation, transduction or conjugation.

True

(T/F) The restriction-modification system always has two genes involved, the cutting enzyme and the methylating enzyme.

True

(T/F) Transduction often involves defective virus.

True

(T/F) Virulent as well as temperate phages can serve as generalized transducing phages.

True

(T/F) Viruses that cause acute infection result in productive infections.

True

(T/F) Plant viruses may be passed from generation to generation of an insect vector.

True.

Productive Infection

Viral infection in which more viral particles are produced.

Latent Infection

Viral infection in which the viral genome is present but not active, so viral particles are not being produced.

Lytic Infection

Viral infection of a host cell with a subsequent production of more virus particles and lysis of the cell.

Acute infections of animals 1. are a result of productive infection. 2. generally lead to long-lasting immunity. 3. result from integration of viral nucleic acid into the host. 4. are usually followed by chronic infections. 5. often lead to tumor formation.

are a result of productive infection AND generally lead to long-lasting immunity.

All phages must have the ability to 1. have their nucleic acid enter the host cell. 2. kill the host cell. 3. multiply in the absence of living bacteria. 4. lyse the host cell. 5. have their nucleic acid replicate in the host cell.

have their nucleic acid enter the host cell AND have their nucleic acid replicate in the host cell.