On what basis are viruses placed in families?

Nucleic acid, symmetry and envelope

Antibacterial antibiotics have no effect on viruses because viruses:

Destroy the drug with their enzymes

Are protected inside an envelope

Virology: structure, classification and cultivation

28 Kerala PSC Lab Technician Gr II practice questions on Virology: structure, classification and cultivation, part of Microbiology. The first 25 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

Question 1 · Medium
On what basis are viruses placed in families?
1. ANucleic acid, symmetry and envelope
2. BThe route by which they spread
3. CThe disease each one produces
4. DThe age group they affect
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Answer: A · Nucleic acid, symmetry and envelope
Classification starts with the type of nucleic acid (DNA or RNA, single or double stranded), then capsid symmetry, presence of an envelope, size and mode of replication. On these grounds mumps and measles viruses sit together in the Paramyxoviridae although their illnesses differ. Clinical features are too variable for classification: one family can cause many diseases and one syndrome can follow many viruses. Genome sequences now guide the finer divisions.
- B: Many unrelated viruses share a route of spread.
- C: One family causes several different diseases, so the illness cannot define it.
- D: Age is a feature of the host, not of the virus.
Question 2 · Easy
A bacteriophage is a virus that infects which group?
1. AFungi
2. BBacteria
3. CInsects
4. DGreen plants
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Answer: B · Bacteria
Bacteriophages, or phages, attach to receptors on the bacterial surface and inject their nucleic acid into the cell. A lytic phage multiplies and bursts the cell, while a temperate phage integrates its genome and may carry genes for toxins, as in diphtheria. Phage typing was long used to subdivide strains of Staphylococcus aureus and Salmonella Typhi in epidemiological work. Phages are counted as plaques on a lawn of host bacteria.
- A: Fungal viruses exist but are not called bacteriophages.
- C: Insect viruses such as the baculoviruses are not phages.
- D: Viruses of green plants are a separate group.
Question 3 · Hard
A nasopharyngeal aspirate from a 5-month-old with bronchiolitis is inoculated into HEp-2 cells. By day 3 the sheet shows large multinucleated cells that round up and detach. Which virus has most likely been isolated?
1. APoliovirus type 1
2. BRespiratory syncytial virus
3. CRotavirus group A
4. DHuman rhinovirus
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Answer: B · Respiratory syncytial virus
Respiratory syncytial virus is the commonest cause of bronchiolitis in infants, and its fusion protein makes infected cells merge, so HEp-2 monolayers show the syncytia that give the virus its name. Rhinoviruses need cultures held at 33°C with rolling and give rounding without syncytia. Rotavirus is a gut virus detected by antigen tests on stool, not by HEp-2 culture. Rapid antigen tests and RT-PCR have largely replaced culture, but the cytopathic effect is still asked for.
- A: Poliovirus causes rounding and lysis without giant cells.
- C: Rotavirus causes diarrhoea and is sought in stool.
- D: Rhinovirus grows at 33°C and does not form syncytia.
Question 4 · Medium
Antibacterial antibiotics have no effect on viruses because viruses:
1. ADestroy the drug with their enzymes
2. BAre protected inside an envelope
3. CMultiply too fast for the drug
4. DHave no cell wall or ribosomes
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Answer: D · Have no cell wall or ribosomes
Penicillins act on peptidoglycan synthesis and most other antibacterials act on bacterial ribosomes, folate synthesis or DNA gyrase, none of which a virus possesses. A virus uses the host cell's ribosomes and enzymes, so antiviral drugs must attack steps unique to the virus, such as its polymerase, protease or reverse transcriptase. Giving antibiotics for a viral fever treats only a bacterial complication. Needless use promotes resistance.
- A: Viruses carry no enzymes that destroy antibacterial drugs.
- B: Naked viruses have no envelope yet are equally unaffected.
- C: Speed of multiplication is not why the drugs fail.
Question 5 · Easy
All of the following are DNA viruses EXCEPT:
1. AAdenovirus
2. BHerpes simplex virus
3. CVaricella-zoster virus
4. DRabies virus
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Answer: D · Rabies virus
Rabies virus is a bullet-shaped RNA virus of the family Rhabdoviridae, with a single negative-sense strand. Herpes simplex and varicella-zoster viruses are enveloped DNA viruses of the family Herpesviridae, and adenoviruses are naked DNA viruses with an icosahedral capsid. The type of nucleic acid is the first division used in virus classification. Among the hepatitis viruses, only hepatitis B carries DNA.
- A: Adenovirus is a naked DNA virus.
- B: Herpes simplex virus is an enveloped DNA virus.
- C: Varicella-zoster virus is a DNA virus of the herpes group.
Question 6 · Medium
Where is influenza vaccine virus grown in large amounts?
1. ABrain of suckling mice
2. BYolk sac of embryonated eggs
3. CAllantoic cavity of embryonated eggs
4. DPeritoneal cavity of mice
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Question 7 · Medium
Why are human diploid cell strains, rather than continuous cell lines, preferred for making human viral vaccines?
1. AThey support every virus equally
2. BThey are not derived from malignant cells
3. CThey grow faster in culture
4. DThey need no serum in the medium
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Question 8 · Easy
The Vero cell line, widely used in virus laboratories, was derived from which tissue?
1. AChick embryo liver
2. BMouse fibroblasts
3. CMonkey kidney
4. DHuman cervix
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Question 9 · Easy
In the influenza virus, which component carries out attachment to the host cell?
1. ANeuraminidase
2. BHaemagglutinin
3. CMatrix protein
4. DNucleoprotein
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Question 10 · Hard
A technician has a 1 in 100 virus suspension and must prepare 5 mL of a 1 in 1,000 dilution. The volumes needed are:
1. A0.5 mL suspension and 4.5 mL diluent
2. B1 mL suspension and 4 mL diluent
3. C0.05 mL suspension and 4.95 mL diluent
4. D5 mL suspension and 0.5 mL diluent
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Question 11 · Medium
Monkey kidney cells taken straight from the animal and grown in the laboratory form a primary cell culture. Such cultures:
1. ASurvive only one or two subcultures
2. BCome from malignant tissue
3. CKeep a normal karyotype for about 50 passages
4. DCan be subcultured indefinitely
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Question 12 · Easy
Which virus family has a single-stranded DNA genome?
1. AHerpesviridae
2. BAdenoviridae
3. CPoxviridae
4. DParvoviridae
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Question 13 · Easy
The protein coat that encloses the nucleic acid of a virus is called the:
1. AVirion
2. BCapsid
3. CEnvelope
4. DPeplomer
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Question 14 · Medium
Enveloped viruses are inactivated by ether and bile, while naked viruses are not. This is because the envelope is made largely of:
1. AProtein coded by the viral genome
2. BDouble-stranded viral RNA
3. CPolysaccharide, like a capsule
4. DLipid from the host cell membrane
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Question 15 · Hard
A faecal suspension is inoculated into monkey kidney cell tubes. Within 18 hours the whole cell sheet has rounded and detached. Fluid from these tubes produces no change in fresh tubes over 10 days, and the uninoculated control stays healthy. The most likely explanation is:
1. AToxicity of the specimen, not a virus
2. BAgeing of an over-confluent monolayer
3. CMycoplasma contaminating the cell line
4. DA rapid enterovirus lost on passage
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Question 16 · Medium
What cytopathic effect does adenovirus typically produce in HEp-2 cells?
1. ALarge syncytia formed by fusion of many cells
2. BSwollen, rounded cells in grape-like clusters
3. CRapid lysis of the entire cell sheet
4. DHaemadsorption with no visible change
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Question 17 · Hard
In a plaque assay, 0.1 mL of a 10^-5 dilution of a virus suspension gives 40 plaques. What is the titre of the undiluted suspension?
1. A4 × 10^8 PFU/mL
2. B4 × 10^7 PFU/mL
3. C4 × 10^5 PFU/mL
4. D4 × 10^6 PFU/mL
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Question 18 · Easy
Suckling mice are the classic laboratory host for isolating which viruses, many of which grow poorly in cell culture?
1. AHerpes simplex viruses
2. BAdenoviruses
3. CCoxsackie A viruses
4. DInfluenza viruses
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Question 19 · Easy
Poxviruses grown in embryonated eggs produce visible pocks when inoculated on the:
1. AAmniotic cavity
2. BChorioallantoic membrane
3. CYolk sac
4. DAllantoic cavity
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Question 20 · Medium
Haemadsorption with guinea pig red cells in a cell culture shows the growth of which viruses?
1. AAdenoviruses and rhinoviruses
2. BHerpes simplex and varicella viruses
3. CInfluenza and parainfluenza viruses
4. DPoliovirus and other enteroviruses
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Question 21 · Medium
Prions, the agents of Creutzfeldt-Jakob disease, differ from viruses in that they:
1. AGrow only in cell cultures
2. BContain no nucleic acid
3. CHave a lipid envelope
4. DAre destroyed by boiling
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Question 22 · Easy
Which group contains the largest viruses that infect humans, just visible by light microscopy after special staining?
1. AParvoviruses
2. BPicornaviruses
3. CPoxviruses
4. DFlaviviruses
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Question 23 · Medium
Measles virus in cell culture typically produces:
1. AMultinucleated giant cells (syncytia)
2. BGrape-like clusters of rounded cells
3. CRapid lysis and complete detachment
4. DSmall foci of enlarged, refractile cells
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Question 24 · Easy
HeLa cells, the first continuous human cell line, came from:
1. ACarcinoma of the cervix
2. BAfrican green monkey kidney
3. CHuman embryonic lung
4. DCarcinoma of the larynx
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Question 25 · Medium
Which of these viruses has a nucleocapsid with helical symmetry?
1. AHerpes simplex virus
2. BAdenovirus
3. CRabies virus
4. DPoliovirus
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Virology: structure, classification and cultivation

On what basis are viruses placed in families?

A bacteriophage is a virus that infects which group?

A nasopharyngeal aspirate from a 5-month-old with bronchiolitis is inoculated into HEp-2 cells. By day 3 the sheet shows large multinucleated cells that round up and detach. Which virus has most likely been isolated?

Antibacterial antibiotics have no effect on viruses because viruses:

All of the following are DNA viruses EXCEPT:

Where is influenza vaccine virus grown in large amounts?

Why are human diploid cell strains, rather than continuous cell lines, preferred for making human viral vaccines?

The Vero cell line, widely used in virus laboratories, was derived from which tissue?

In the influenza virus, which component carries out attachment to the host cell?

A technician has a 1 in 100 virus suspension and must prepare 5 mL of a 1 in 1,000 dilution. The volumes needed are:

Monkey kidney cells taken straight from the animal and grown in the laboratory form a primary cell culture. Such cultures:

Which virus family has a single-stranded DNA genome?

The protein coat that encloses the nucleic acid of a virus is called the:

Enveloped viruses are inactivated by ether and bile, while naked viruses are not. This is because the envelope is made largely of:

A faecal suspension is inoculated into monkey kidney cell tubes. Within 18 hours the whole cell sheet has rounded and detached. Fluid from these tubes produces no change in fresh tubes over 10 days, and the uninoculated control stays healthy. The most likely explanation is:

What cytopathic effect does adenovirus typically produce in HEp-2 cells?

In a plaque assay, 0.1 mL of a 10^-5 dilution of a virus suspension gives 40 plaques. What is the titre of the undiluted suspension?

Suckling mice are the classic laboratory host for isolating which viruses, many of which grow poorly in cell culture?

Poxviruses grown in embryonated eggs produce visible pocks when inoculated on the:

Haemadsorption with guinea pig red cells in a cell culture shows the growth of which viruses?

Prions, the agents of Creutzfeldt-Jakob disease, differ from viruses in that they:

Which group contains the largest viruses that infect humans, just visible by light microscopy after special staining?

Measles virus in cell culture typically produces:

HeLa cells, the first continuous human cell line, came from:

Which of these viruses has a nucleocapsid with helical symmetry?