There are several factors that virologists use to classify viruses. Some of these factors include i) type of nucleic acid; ii) presence of an envelope; iii) size and shape of the virus; iv) morphology of the capsid; and v) how the virus reproduces. Lauren, a seasoned animal virologist, has started researching bacteriophages, viruses that are able to infect bacteria. While growing bacteria in the lab, Lauren notices that her samples are not growing properly. She thinks that she may have contaminated her bacterial cultures accidentally. Lauren thinks back through the process of adding the bacteria to the media--perhaps she used a flask that had not been cleaned properly, or the media were contaminated prior to use. The first thing Lauren does is visualize her culture underneath the electron microscope, a microscope powerful enough to magnify the bacteriophage if present. As soon as Lauren begins her microscopy, she notices a small organism that looks like it has a head and legs! Lauren then starts the journey of classifying this virus by recording her observations.

Think about the many factors that are used to classify viruses. In order for Lauren to determine the type of virus she may have, she needs to understand some basic concepts about how viruses are characterized.