Compare the structures of tobacco mosaic virus (TMV) and influenza virus (see Figure 19.3)

TMV is a rod-shaped virus that consists of a single helical RNA molecule. TMV is 300 nm in length and 18 nm in diameter. The RNA molecule is surrounded by a protein coat which is called a capsid.

A capsid is a shell of proteins that covers the genetic material of the virus.

Influenza is a spherical virus that is about 80 to 200 nm in diameter. It is covered by an outer envelope that bears numerous glycoprotein spikes. It consists of eight double-helical RNA molecules that are associated with proteins to form an RNA protein complex.

Further, each RNA-protein complex is associated with a viral polymerase.

Both TMV and influenza virus contains RNA as the genetic material. However, TMV has one RNA molecule, whereas influenza has eight RNA molecules. The RNA in both viruses is associated with proteins.

Influenza virus contains an outer envelope, whereas TMV virus lacks a protein coat. TMV is a rod-shaped virus, whereas the influenza virus is spherical. Thus, the primary difference between the structures of the two viruses is the amount of genetic material and the presence and absence of an outer envelope.