Viruses Questions and Answers

Answer: B

Correct answer: single or double stranded, and linear or circular

Viruses use every arrangement of nucleic acid found in nature and some found nowhere else: DNA or RNA, single or double stranded, linear, circular or segmented, and in the case of single-stranded RNA either positive or negative sense. No other group of infectious agents shows this variety, and it is one of the reasons virus classification rests on genome type.

Answer: C

Protomers add along the genome, so a longer genome gives a longer particle while the diameter stays fixed. An icosahedral capsid behaves the other way: it is a closed container of set size, which limits how much nucleic acid will fit.

Answer: D

Encoding one subunit and repeating it costs far less genetic information than encoding a large unique shell, which matters when the genome is small. The symmetry of the icosahedron is what makes such repetition geometrically possible.

Answer: A

Correct answer: between the nucleocapsid and the envelope

The matrix protein forms a layer lining the inner face of the envelope and contacting the nucleocapsid, so it links the two. That position is what makes it structurally important: it gives the envelope its rigidity and it directs assembly, gathering the nucleocapsid beneath the patch of membrane carrying the viral glycoproteins so that budding produces a complete particle.

Answer: B

A protein capsid survives stomach acid, bile and drying far better than a lipid envelope, so naked viruses persist in the environment and on surfaces. Enveloped viruses more often need close or moist contact because their lipid is fragile.

Answer: C

The envelope is host-derived lipid, and once it is damaged the glycoproteins it carries can no longer bring about attachment and entry. That fragility shapes how such viruses spread and how easily they are disinfected.

Answer: D

Correct answer: visible damage to cells caused by viral infection

The cytopathic effect is what the infection does to the cell as seen down the microscope - rounding, detachment, syncytium formation, inclusion bodies, lysis. It is the basis of detecting a virus in cell culture, and the pattern is often characteristic enough to suggest which virus is present before any other test is done.

Answer: A

Correct answer: infected cells have died, leaving a clear area

A plaque is a hole in the monolayer. One infectious particle infects one cell, the progeny spread to the neighbours under a semi-solid overlay that prevents diffusion, and the successive rounds of killing leave a clear patch against the stained sheet of surviving cells. Because each plaque traces back to a single particle, counting plaques counts infectious units.

Answer: B

Carrying one type of nucleic acid rather than both is one of the clearest distinctions, alongside the absence of ribosomes and of energy generation. Bacteria are cells and divide in two; viruses are assembled from separately made parts.

Answer: C

Correct answer: Growth in size before dividing

Viruses do not grow and divide. They are assembled from separately synthesised components, so a cell yields hundreds of complete particles at once rather than a parent particle enlarging and splitting. The other three are all defining properties: a protein coat, a nucleic acid genome, and replication only inside a host cell.