What are the characteristics of viruses?

One main characteristic is that a virus’s genetic material can be DNA or RNA. The DNA or RNA can be arranged in a straight line (linear) or a loop (circular). It can also possess  ssDNA, dsDNA, while RNA are typically single-stranded but there are some double-stranded RNA viruses. The RNA can also be positive-sense RNA, directly used to make new virus components, while negative-sense RNA needs to be converted into positive-sense RNA first. Another characteristic is that viruses are extremely small, typically between 20 to 400 nanometers (nm) in size. Sizes and molecular weights can vary widely; for example, the measles virus is much larger than the Zika virus. Additionally, viruses can possess different shapes. One shape is icosahedral, which has many sides. Many viruses that infect people have this shape. Another shape is helical, and resembles a cylinder. The genetic material of this virus is wound up in a spiral, similar to a spring. There are also complex viruses, which combine different shapes, such as a polyhedral head attached to a helical tail. Many bacteriophages have this structure. Spherical viruses are either helical or polyhedral viruses with an additional envelope, giving them a round appearance. Viruses can also mutate to form different strains of the same virus and replicate at a high rate.