Viruses Questions and Answers

Answer: B

In helical symmetry the protomers wind around the genome in a spiral, so the length of the particle is set by the length of the nucleic acid rather than by the coat. Icosahedral capsids instead form a closed shell of fixed size, and complex describes particles that are neither.

Answer: C

The icosahedron has axes of fivefold, threefold and twofold rotation, written 532, which is what allows a closed shell to be built from many copies of one protein. That economy matters because a small genome cannot encode a large, unique container.

Answer: D

The envelope is taken from the plasma membrane or another host membrane as the particle leaves, and the virus contributes only the glycoproteins embedded in it. Because the lipid is host derived, an enveloped virus is readily inactivated by solvents and detergents.

Answer: A

The envelope is a lipid bilayer, so anything that disrupts lipid destroys the particle's ability to attach and fuse. Naked viruses have only protein on the outside and survive drying, acids and detergents far better, which is reflected in how each group is transmitted.

Answer: B

Spikes, also called peplomers, are virus-coded glycoproteins embedded in the host-derived envelope, and they carry the attachment function. Capsomeres and protomers are parts of the protein capsid, and fimbriae are bacterial structures.

Answer: C

Plus-sense RNA reads in the same direction as mRNA, so a ribosome can translate the genome as soon as it reaches the cytoplasm and the naked nucleic acid alone is infectious. Minus-sense RNA reads the opposite way and must first be copied, which is why such viruses carry their own polymerase.

Answer: D

The host has no enzyme able to copy RNA into RNA, and a minus-sense genome cannot be translated as it stands, so the polymerase must arrive packaged in the virion. Reverse transcriptase is what retroviruses carry instead, and no virus carries a ribosome.

Answer: A

A retrovirus has a plus-sense RNA genome but does not translate it directly; reverse transcriptase copies it into DNA, which then integrates into the host chromosome. That enzyme is the defining feature, and it travels inside the virion because no cell provides one.

Answer: B

A genome is always nucleic acid, so there is no protein class; the six classes are double- and single-stranded DNA, double-stranded RNA, plus- and minus-sense single-stranded RNA, and the retroviruses. Prions are proteinaceous but are not viruses and have no genome.

Answer: C

Attachment is the specific binding of a virion protein, the anti-receptor, to a constituent of the cell surface, and it decides which cells a virus can enter at all. Penetration, uncoating, synthesis, maturation and egress follow in that order.