Chapter 6 - Acellular Pathogens

Question 1

The component(s) of a virus that is/are extended from the envelope for attachment is/are the:

A) Capsomeres.
B) Spikes.
C) Nucleic acid.
D) Viral whiskers.

Answer 1

Correct Answer: B) Spikes.

Explanation: Spikes are glycoprotein projections that extend from the viral envelope and allow the virus to attach to specific receptors on a host cell’s surface.

Question 2

Which of the following does a virus lack? Select all that apply.

A) Ribosomes.
B) Metabolic processes.
C) Nucleic acid.
D) Glycoprotein.

Answer 2

Correct Answers: A) and B).

Explanation: Viruses lack both ribosomes and independent metabolic processes, which is why they must hijack host-cell machinery for protein synthesis and energy use.

Question 3

The envelope of a virus is derived from the host’s:

A) Nucleic acids.
B) Membrane structures.
C) Cytoplasm.
D) Genome.

Answer 3

Correct Answer: B) Membrane structures.

Explanation: During release, enveloped viruses acquire a lipid bilayer from the host’s plasma or nuclear membrane, incorporating viral glycoproteins into it.

Question 4

In naming viruses, the family name ends with (BLANK) and the genus name ends with (BLANK).

A) −Virus; −Viridae.
B) −Viridae; −Virus.
C) −Virion; Virus.
D) −Virus; Virion.

Answer 4

Correct Answer: B) −Viridae; −Virus.

Explanation: By convention, viral family names end in −viridae (e.g., Herpesviridae) and genus names end in −virus (e.g., Simplexvirus).

Question 5

What is another name for a nonenveloped virus?

A) Enveloped virus.
B) Provirus.
C) Naked virus.
D) Latent virus.

Answer 5

Correct Answer: C) Naked virus.

Explanation: Viruses that lack a lipid envelope are called naked viruses; their outermost layer is the protein capsid.

Question 6

Which of the following are characteristics of viruses?

A) Genome is surrounded by a protein capsid.
B) Infectious, acellular pathogens.
C) Obligate intracellular parasites with host and cell-type specificity.
D) All of these.

Answer 6

Correct Answer: D) All of these.

Explanation: Viruses are acellular, infectious particles with a genome enclosed in a capsid, and they require specific host cells for replication, showing both host and cell-type specificity.

Question 7

The naked atadenovirus uses spikes made of (BLANK) from its capsid to bind to host cells.

A) Lipids.
B) Carbohydrates.
C) None of these.
D) Glycoproteins.

Answer 7

Correct Answer: D) Glycoproteins.

Explanation: Some naked viruses, such as atadenoviruses, have glycoprotein spikes extending from the capsid that help them attach to host receptors.

Question 8

Which of the following leads to the destruction of the host cells?

A) Lysogenic cycle.
B) Lytic cycle.
C) Prophage.
D) Temperate phage.

Answer 8

Correct Answer: B) Lytic cycle.

Explanation: In the lytic cycle, new virions are assembled and released through host-cell lysis, destroying the cell.

Question 9

A virus obtains its envelope during which of the following phases?

A) Attachment.
B) Penetration.
C) Assembly.
D) Release.

Answer 9

Correct Answer: D) Release.

Explanation: Enveloped viruses typically acquire their envelope by budding from the host membrane as they exit during the release stage.

Question 10

Which of the following components is brought into a cell by HIV?

A) A DNA-dependent DNA polymerase.
B) RNA polymerase.
C) Ribosome.
D) Reverse transcriptase.

Answer 10

Correct Answer: D) Reverse transcriptase.

Explanation: HIV carries its own reverse transcriptase enzyme to synthesize DNA from its RNA genome once inside the host cell.

Question 11

A positive-strand RNA virus:

A) Must first be converted to an mRNA before it can be translated.
B) Can be used directly to translate viral proteins.
C) Will be degraded by host enzymes.
D) Is not recognized by host ribosomes.

Answer 11

Correct Answer: B) Can be used directly to translate viral proteins.

Explanation: Positive-strand RNA viruses already have an RNA genome with the same polarity as mRNA, allowing host ribosomes to translate it directly into viral proteins.

Question 12

What is the name for the transfer of genetic information from one bacterium to another bacterium by a phage?

A) Transduction.
B) Penetration.
C) Excision.
D) Translation.

Answer 12

Correct Answer: A) Transduction.

Explanation: During transduction, a bacteriophage accidentally packages bacterial DNA and transfers it to another bacterium, enabling horizontal gene transfer.

Question 13

With a few exceptions, RNA viruses that infect animal cells replicate in the (BLANK).

A) Cytoplasm.
B) Ribosomes.
C) Mitochondria.
D) Nucleus.

Answer 13

Correct Answer: A) Cytoplasm.

Explanation: Most RNA viruses replicate in the cytoplasm of animal cells using host ribosomes and viral polymerases; DNA viruses typically replicate in the nucleus.

Question 14

Not all animal viruses undergo replication by the lytic cycle. There are viruses that are capable of remaining hidden or dormant inside the cell in a process called (BLANK).

A) Latency.
B) Persistence.
C) Dormancy.
D) Transcriptase.

Answer 14

Correct Answer: A) Latency.

Explanation: Some viruses can remain dormant in host cells without causing immediate lysis; this is known as latency. Latent viruses can later reactivate under certain conditions (e.g., herpesviruses).

Question 15

The third stage of a viral infection is (BLANK) of new viral components.

A) Penetration.
B) Biosynthesis.
C) Maturation.
D) Attachment.

Answer 15

Correct Answer: B) Biosynthesis.

Explanation: During the biosynthesis stage, the viral genome directs the host cell to produce viral components such as nucleic acids and proteins before assembly.

Question 16

A virus that infects a bacterium is called a/an (BLANK).

A) Bacteriophage.
B) Eclipse.
C) Viron.
D) Prion.

Answer 16

Correct Answer: A) Bacteriophage.

Explanation: Bacteriophages are viruses that specifically infect and replicate within bacteria, using either lytic or lysogenic cycles.

Question 17

Which of the following cannot be used to culture viruses?

A) Tissue culture.
B) Liquid medium only.
C) Embryo.
D) Animal host.

Answer 17

Correct Answer: B) Liquid medium only.

Explanation: Viruses require living cells to replicate, so they cannot grow in nutrient broth or any cell-free liquid medium.

Question 18

Which of the following tests can be used to detect the presence of a specific virus?

A) EIA.
B) RT-PCR.
C) PCR.
D) All of the above.

Answer 18

Correct Answer: D) All of the above.

Explanation: Enzyme immunoassay (EIA), PCR, and RT-PCR are all molecular or immunological tests used to identify viruses by detecting viral proteins or nucleic acids.

Question 19

Which of the following is NOT a cytopathic effect?

A) Transformation.
B) Cell fusion.
C) Mononucleated cell.
D) Inclusion bodies.

Answer 19

Correct Answer: C) Mononucleated cell.

Explanation: Cytopathic effects are visible host-cell changes from viral infection (e.g., transformation, syncytia formation, inclusion bodies). A normal mononucleated cell is not a cytopathic effect.

Question 20

Match the virus detection method of EIA to its proper description.

A) Using primers to amplify DNA.
B) Using antibodies to detect viral antigens (proteins).
C) Making cDNA from RNA.
D) Isolating antibodies from a patient, adding them to a virus, and seeing if the virus can clump erythrocytes.

Answer 20

Correct Answer: B) Using antibodies to detect viral antigens (proteins).

Explanation: The enzyme immunoassay (EIA) test identifies viral proteins (antigens) by using specific antibodies bound to an enzyme that produces a detectable signal.

Question 21

Which of the following statements are true regarding HeLa cells? (Select all that apply.)

A) These HeLa cell lines allow scientists to culture and study viruses.
B) Viruses are facultative intracellular entities.
C) HeLa cells were tumor cells isolated from Henrietta Lacks.
D) They were used to develop the first continuous tissue-culture cell line.

Answer 21

Correct Answers: A), C), and D).

Explanation: HeLa cells, derived from Henrietta Lacks’ cervical tumor, were the first immortal human cell line and have been crucial for studying viruses and developing vaccines.

Question 22

Until the late 1930s and the advent of the (BLANK) microscope, no one had seen a virus.

A) Compound.
B) Electron.
C) Inverted.
D) Light.

Answer 22

Correct Answer: B) Electron.

Explanation: The invention of the electron microscope allowed visualization of viruses for the first time, revealing their structure and confirming their existence as acellular pathogens.

Question 23

Although there are no current treatments for prion infections, which of the following could be used?

A) Sulfa drugs.
B) Nucleases.
C) Proteases.
D) Antibiotics.

Answer 23

Correct Answer: C) Proteases.

Explanation: Prions are infectious proteins without nucleic acids; theoretically, proteases can degrade them, while nucleases and antibiotics target nucleic acids and bacteria, respectively.

Question 24

Viruses that infect plants are considered (BLANK) parasites, which means that they can establish an infection without killing the host.

A) Biotrophic.
B) Heteromorphic.
C) Osmotic.
D) Pathogenic.

Answer 24

Correct Answer: A) Biotrophic.

Explanation: Plant viruses are often biotrophic, meaning they coexist with living host tissue and replicate without immediately killing the plant cells.

Question 25

Unlike bacteria, many of which can be grown on an artificial nutrient medium, (BLANK) require a living (BLANK) cell for replication. A) Viruses, endoparasitic. B) Plants, ectoparasitic. C) Animals, endoparasitic. D) Viruses, host.

Answer 25

Correct Answer: D) Viruses, host. Explanation: Viruses cannot replicate outside of living cells and depend entirely on host cellular machinery for reproduction.

Question 26

An example of an immortal cell line is the HeLa cell line, which was originally cultivated from tumor cells obtained from (BLANK), a patient who died of cervical cancer in 1951. A) Henrietta Lacks. B) Harry Lacks. C) Henrietta Lucas. D) Henrietta Leeks.

Answer 26

Correct Answer: A) Henrietta Lacks. Explanation: The HeLa cell line, derived from Henrietta Lacks’ cervical tumor, became the first immortal human cell line used extensively in virology and medical research.

Question 27

Which of these infectious agents do not have nucleic acid? A) Viroids. B) Viruses. C) Bacteria. D) Prions.

Answer 27

Correct Answer: D) Prions. Explanation: Prions are infectious misfolded proteins containing no DNA or RNA, distinguishing them from viruses, viroids, and all cellular life.

Question 28

Which of the following is true of prions? A) They can be inactivated by boiling at 100 °C. B) They contain a capsid. C) They are a rogue form of protein, PrP. D) They can be reliably inactivated by an autoclave.

Answer 28

Correct Answer: C) They are a rogue form of protein, PrP. Explanation: Prions are abnormal, misfolded versions of the normal PrP protein that induce other proteins to misfold; they lack capsids and resist standard heat sterilization.

Question 29

Which of the following are true regarding viroids, virusoids, and prions? (Select all that apply) A) A prion is a misfolded rogue form of a normal protein found in the cell. B) Virusoids require that the cell also be infected with a specific “helper” virus. C) The first viroid discovered was found to cause potato tuber spindle disease. D) Viroids cannot replicate their genome in host cells.

Answer 29

Correct Answers: A), B), and C). Explanation: Viroids are infectious naked RNAs that replicate in plants; virusoids need a helper virus for replication; and prions are infectious proteins with no nucleic acids.

Question 30

An acellular entity composed of a small circular RNA molecule without a capsid and not capable of replicating its genome is known as which of the following? A) Bacteria. B) Provirus. C) Virion. D) Viroid.

Answer 30

Correct Answer: D) Viroid. Explanation: A viroid is a tiny, circular RNA molecule that infects plants and lacks a protein coat. A virion, however, is a complete virus particle with a protective capsid (and sometimes an envelope). Memory hook: Think “viroid is void” — it’s void of all the extra parts a full virion has.