Part 6 — Viruses and Viroids (Q126–Q150)
Part 6 — Viruses and Viroids (Q126–Q150)
25 MCQs on viral structure, bacteriophages, retroviruses, replication cycles, prions, viroids, and role in disease.
Q126. Viruses are considered living because they:
- A. Possess DNA or RNA and can reproduce inside host cells
- B. Have cell organelles
- C. Have ribosomes
- D. Can metabolize independently
Answer: A
- A: Correct — viruses have genetic material and reproduce only in host cells.
- B: Incorrect — they lack organelles.
- C: Incorrect — no ribosomes present.
- D: Incorrect — cannot metabolize outside host.
Q127. Viruses outside the host cell are:
- A. Active
- B. Inert crystalline structures
- C. Metabolically functional
- D. Photosynthetic
Answer: B
- A: Incorrect.
- B: Correct — inert and crystallizable outside host.
- C: Incorrect.
- D: Incorrect.
Q128. Genetic material of HIV is:
- A. Double-stranded DNA
- B. Single-stranded RNA
- C. Single-stranded DNA
- D. Double-stranded RNA
Answer: B
- A: Incorrect.
- B: Correct — retroviruses like HIV contain ssRNA.
- C: Incorrect.
- D: Incorrect.
Q129. Bacteriophage infects:
- A. Plants
- B. Animals
- C. Bacteria
- D. Fungi
Answer: C
- A: Incorrect.
- B: Incorrect.
- C: Correct — bacteriophages are viruses infecting bacteria.
- D: Incorrect.
Q130. The protein coat of virus is called:
- A. Envelope
- B. Capsid
- C. Cell wall
- D. Capsule
Answer: B
- A: Incorrect — envelope is outer lipid layer in some viruses.
- B: Correct — capsid made of capsomeres.
- C: Incorrect.
- D: Incorrect.
Q131. Which enzyme is present in retroviruses?
- A. DNA polymerase I
- B. Reverse transcriptase
- C. RNA polymerase
- D. Ligase
Answer: B
- A: Incorrect.
- B: Correct — reverse transcriptase converts viral RNA to DNA.
- C: Incorrect.
- D: Incorrect.
Q132. Tobacco Mosaic Virus (TMV) contains:
- A. DNA
- B. RNA
- C. Both DNA and RNA
- D. Protein only
Answer: B
- A: Incorrect.
- B: Correct — TMV is RNA virus.
- C: Incorrect — never both.
- D: Incorrect.
Q133. Viruses differ from viroids in having:
- A. Only RNA
- B. RNA with protein coat
- C. DNA only
- D. No nucleic acid
Answer: B
- A: Incorrect — viroids have only RNA.
- B: Correct — viruses have RNA/DNA with protein coat.
- C: Incorrect.
- D: Incorrect.
Q134. The lytic cycle results in:
- A. Integration of viral DNA
- B. Immediate lysis of host cell
- C. Latency in host genome
- D. Transformation only
Answer: B
- A: Incorrect — lysogenic cycle.
- B: Correct — lytic cycle ends with lysis and release of new virions.
- C: Incorrect.
- D: Incorrect.
Q135. The lysogenic cycle is characterized by:
- A. Viral genome integrates into host DNA
- B. Immediate host lysis
- C. Lack of replication
- D. No infection
Answer: A
- A: Correct — viral DNA integrates and replicates passively.
- B: Incorrect.
- C: Incorrect.
- D: Incorrect.
Q136. Viroids are composed of:
- A. DNA + protein coat
- B. RNA only
- C. DNA only
- D. RNA + protein + lipid
Answer: B
- A: Incorrect.
- B: Correct — viroids are naked RNA without protein coat.
- C: Incorrect.
- D: Incorrect.
Q137. Prions differ from viruses as they lack:
- A. Protein
- B. Nucleic acid
- C. Infectivity
- D. Pathogenicity
Answer: B
- A: Incorrect — prions are only protein.
- B: Correct — prions lack nucleic acids.
- C: Incorrect — they are infectious.
- D: Incorrect — prions are pathogenic.
Q138. Which disease is caused by prions?
- A. AIDS
- B. Mad cow disease (BSE)
- C. Polio
- D. Hepatitis
Answer: B
- A: Incorrect — caused by HIV.
- B: Correct — bovine spongiform encephalopathy by prions.
- C: Incorrect.
- D: Incorrect.
Q139. Which disease is caused by viroids?
- A. Potato spindle tuber disease
- B. Citrus canker
- C. Tobacco mosaic
- D. Influenza
Answer: A
- A: Correct — potato spindle tuber disease.
- B: Incorrect — bacterial disease.
- C: Incorrect — viral disease.
- D: Incorrect — viral flu.
Q140. Capsomeres are:
- A. Subunits of capsid
- B. Nucleic acids
- C. Viral enzymes
- D. Lipid molecules
Answer: A
- A: Correct — protein subunits making up capsid.
- B: Incorrect.
- C: Incorrect.
- D: Incorrect.
Q141. Which viral disease is eradicated from the world?
- A. Smallpox
- B. Measles
- C. Polio
- D. Rabies
Answer: A
- A: Correct — smallpox eradicated by vaccination.
- B: Incorrect — measles still present.
- C: Incorrect — polio not eradicated worldwide.
- D: Incorrect — rabies exists.
Q142. The first virus discovered was:
- A. HIV
- B. TMV
- C. Polio virus
- D. Influenza virus
Answer: B
- A: Incorrect.
- B: Correct — Tobacco Mosaic Virus (TMV).
- C: Incorrect.
- D: Incorrect.
Q143. Viruses are obligate parasites because:
- A. They lack ribosomes
- B. Cannot make energy or proteins outside host
- C. Require host enzymes
- D. All of these
Answer: D
- A: Correct.
- B: Correct.
- C: Correct.
- D: Correct — all reasons.
Q144. Which of the following is RNA virus?
- A. HIV
- B. Influenza
- C. TMV
- D. All of these
Answer: D
- A: Correct — HIV.
- B: Correct — influenza virus.
- C: Correct — TMV.
- D: Correct.
Q145. Common cold is caused by:
- A. Rhinovirus
- B. Adenovirus
- C. HIV
- D. Plasmodium
Answer: A
- A: Correct — rhinoviruses.
- B: Incorrect — adenoviruses cause other infections.
- C: Incorrect.
- D: Incorrect.
Q146. Which of the following is a DNA virus?
- A. Hepatitis B virus
- B. HIV
- C. Influenza
- D. TMV
Answer: A
- A: Correct — Hepatitis B is DNA virus.
- B: Incorrect — RNA virus.
- C: Incorrect.
- D: Incorrect.
Q147. Viral envelopes are derived from:
- A. Host cell membrane
- B. Viral capsid
- C. Nucleus
- D. Mitochondria
Answer: A
- A: Correct — envelopes from host plasma membrane.
- B: Incorrect.
- C: Incorrect.
- D: Incorrect.
Q148. Which statement is true about viruses?
- A. Contain both DNA and RNA
- B. Only one type of nucleic acid
- C. No protein coat
- D. Are prokaryotes
Answer: B
- A: Incorrect — either DNA or RNA, never both.
- B: Correct — only one type present.
- C: Incorrect — have protein coat.
- D: Incorrect — not prokaryotes.
Q149. Viroids differ from viruses in lacking:
- A. DNA
- B. Protein coat
- C. Infectivity
- D. RNA
Answer: B
- A: Incorrect.
- B: Correct — viroids = naked RNA without coat.
- C: Incorrect — they are infectious.
- D: Incorrect.
Q150. Prions cause disease by:
- A. Altering host protein folding
- B. Inserting DNA into genome
- C. Producing toxins
- D. Replicating RNA
Answer: A
- A: Correct — prions induce abnormal protein folding.
- B: Incorrect.
- C: Incorrect.
- D: Incorrect. (more…)