Some viruses can be crystallized and their structures analyzed. one such virus is yellow mottle virus, which infects beans. this virus has a single-stranded rna genome containing about 6,300 nucleotides. its capsid is 25–30 nm in diameter and contains 180 identical capsomeres. if the yellow mottle virus capsid has 20 facets, how many proteins form each facet?

The correct answer is 9 proteins form each of the 20 facets of this virus. A capsid is the protein shell that surrounds a virus. A capsomere is the subunit of the capsid. Depending on the virus, capsomeres arrange in many different shapes to form the capsid. The yellow mottle virus has 20 facets, this means that it has an icosahedral capsid. Since it contains 180 identical capsomeres, we can conclude that 9 proteins form each facet.