A virus is an ultramicroscopic, obligate, intracellular parasite incapable of autonomous replication. Ultramicroscopic means, as you might expect, very small. Viruses are much, much smaller than either prokaryotic or eukaryotic cells. A typical virus is on the order of 20 to 300 nanometers in diameter. (A nanometer is 1/1000 of a micrometer, which is 1/1,000,000 of a meter.) It’s intracellular because it lives inside cells. And an obligate parasite is one that can only exist through parasitism.
Basic question answer in virology
1. The first virus recognized as such was
(c) tobacco mosaic virus.
(d) potato blight.
2. Viruses are
(c) tiny bacteria.
(d) mutated algae.
3. A capsid is
(a) the protein coat of a virus.
(b) a tight cap worn by viral researchers.
(c) a European flower often infected by a viral disease.
(d) a cell that’s been infected by a virus.
4. Viruses that attack bacteria are called
5. For the host cell, the lytic cycle ends when
(a) it replicates.
(b) it bursts open.
(c) it collapses.
(d) it becomes cancerous.
6. The phage life cycle which does not kill the host cell is called
(a) the merciful cycle.
(b) the nonlytic cycle.
(c) the semiphage cycle.
(d) the lysogenic cycle.
7. The life cycle of eukaryotic viruses is
(a) shorter than that of phages.
(b) about the same as that of phages.
(c) longer than that of phages.
(d) longer for plants, shorter for animals.
8. An enveloped virus has
(a) a lipid membrane picked up from the host cell.
(b) a very thick capsid.
(c) a very long tail.
(d) been swallowed by a white blood cell.
9. HIV and some other retroviruses have
(a) fewer genes than other viruses.
(b) no protein coat.
(c) extra genes not required for their own replication.
(d) DNA that reads in the opposite direction to other viruses.
10. Viroids are
(a) extremely tiny RNA genomes.
(b) dead viruses.
(c) artificial viruses constructed using nanotechnology.
(d) glands in the throat that often become inflamed.