Free Viruses MCQs with Answers

• A. are smaller than any known bacterium
• B. carry both DNA and RNA in the same particle
• C. have a cell wall made of peptidoglycan
• D. lack the ribosomes and enzymes needed to make their own proteins and ATP

Explanation: A virus particle has nucleic acid and protein but no ribosomes, no respiratory enzymes and no ATP generating system, so it can only…

• A. capsid
• B. capsomere
• C. envelope
• D. nucleoid

Explanation: The capsid is the complete protein shell around the viral nucleic acid, and it protects the genome and helps the virus attach to the host…

• A. double stranded DNA
• B. single stranded DNA
• C. single stranded RNA
• D. double stranded RNA

Explanation: TMV is a rod shaped plant virus whose genome is a single strand of RNA wound in a helix inside about 2,130 identical capsomeres.

• A. head
• B. tail fibres
• C. collar
• D. sheath

Explanation: The tail fibres carry the binding proteins that fit specific receptor molecules on the bacterial cell wall, which is why a phage infects…

• A. Synthesis of viral coat proteins
• B. Injection of viral nucleic acid into the host
• C. Attachment of the virus to the host cell
• D. Integration of viral DNA into the host chromosome

Explanation: In lysogeny the phage DNA becomes part of the bacterial chromosome as a prophage and is copied silently every time the bacterium divides…

• A. prophage
• B. provirus
• C. prion
• D. viroid

Explanation: Prophage is the term reserved for phage DNA sitting integrated and inactive in a bacterial chromosome.

• A. They can be crystallised like a chemical substance
• B. They are destroyed by antibiotics such as penicillin
• C. They contain either DNA or RNA but never both
• D. They multiply only inside a living host cell

Explanation: Antibiotics act on structures and pathways that only cells have, such as peptidoglycan wall synthesis or bacterial ribosomes, and a virus…

• A. prions
• B. bacteriophages
• C. viroids
• D. capsomeres

Explanation: Viroids are short circular RNA molecules with no capsid at all, and they cause plant diseases such as potato spindle tuber disease.

• A. RNA only
• B. DNA only
• C. an envelope of host lipid
• D. no nucleic acid at all

Explanation: A prion is a misfolded form of a normal cellular protein that converts healthy copies of that protein into the same abnormal shape, so…

• A. 20 to 300 nm
• B. 20 to 300 um
• C. 1 to 10 mm
• D. 0.5 to 5 um

Explanation: Viruses are measured in nanometres, from about 20 nm for the smallest to roughly 300 nm for the largest such as poxviruses, which is why…

• A. protein synthesised by the viral genome alone
• B. the membrane of the host cell it budded from
• C. the nucleic acid core of the virus
• D. capsomeres rearranged after assembly

Explanation: As the assembled particle buds out of an infected cell it wraps itself in a patch of the host's plasma membrane or nuclear membrane, so…

• A. antibodies secreted by plasma cells that neutralise virus particles
• B. antibiotics that block viral protein synthesis
• C. glycoproteins released by infected cells that make neighbouring cells resistant
• D. enzymes that digest the viral capsid in the bloodstream

Explanation: An infected cell secretes interferon, which binds receptors on nearby uninfected cells and switches on genes whose products block viral…

• A. Poliomyelitis
• B. Measles
• C. Hepatitis B
• D. Smallpox

Explanation: Smallpox was declared eradicated by the WHO in 1980 after a global vaccination campaign, helped by the fact that the virus had no animal…

• A. Dmitri Ivanovsky
• B. Louis Pasteur
• C. Alexander Fleming
• D. Edward Jenner

Explanation: In 1892 Ivanovsky filtered sap from diseased tobacco plants and found the filtrate still infectious, proving the agent was smaller than…

• A. sterile nutrient agar plates
• B. living cells, such as chick embryos or cell cultures
• C. rich broth shaken with oxygen
• D. extracts of sterile soil

Explanation: Because viruses have no metabolism of their own, they multiply only inside living host cells, so laboratories use cell cultures, chick…

• A. viroids
• B. plasmids
• C. bacteriophages
• D. prions

Explanation: Bacteriophages attach to specific receptors on the bacterial surface and inject their nucleic acid, making them powerful tools of genetics…

• A. influenza virus
• B. poliovirus
• C. HIV
• D. tobacco mosaic virus

Explanation: Wendell Stanley crystallised tobacco mosaic virus in 1935 and the crystals remained infectious, blurring the line between living and non…

• A. a head containing nucleic acid attached to a protein tail with tail fibres
• B. an RNA core surrounded by a lipid envelope only
• C. a single infectious protein molecule
• D. DNA enclosed in a polysaccharide capsule

Explanation: The phage's icosahedral head packs the DNA, and the hollow tail with base plate and fibres anchors to the bacterium and injects the…

• A. integration of viral DNA into the host chromosome
• B. bursting of the bacterium and release of new phage particles
• C. the virus becoming permanently dormant
• D. the bacterium turning into a virus

Explanation: After multiplication and assembly, lysozyme made by the phage dissolves the bacterial wall and the progeny escape to infect fresh cells.

• A. Cholera
• B. Tuberculosis
• C. Poliomyelitis
• D. Typhoid

Explanation: Polio is caused by the poliovirus, which attacks motor neurones and can cause paralysis.