Chapter 6, Problem 1CHI

Many classification schemes are used to identify bacteria. These start with Gram staining, progress to morphology and arrangement characteristics, and include a battery of metabolic tests. Build an analogous scheme that could be used to identify viruses. You might start by considering the host, or you might start with viruses found in a particular environment, such as a marine filtrate.

Summary Introduction

Virion refers to the complete virus particle and a simplest virion comprise only a nucleocapsid and capsid. Nucleocapsid possesses a nucleic acid (RNA or DNA), and a capsid refers to a protein coat. Enveloped virus refers to the viruses possessing an envelope, whereas naked or non-enveloped virus refers to those viruses lacking an envelope. Capsid symmetry is of three types, namely complex, icosahedral, and helical. Most of the viruses possess either helical or icosahedral capsids. Virus is a distinct group of infectious agent responsible for causing several diseases in human. They can exist both intracellularly and extracellularly. Viruses have the ability to infect all known cell types, including bacteria, archaea, fungi, protists, plants, and animals.

Explanation of Solution

Primarily, students should determine various characteristic features of viruses that are appropriately common to differentiate them into two to three major groups and then categorize them further.

The content of nucleic acid (DNA or RNA) of viruses should be determined first. Further, other characteristics such as capsid geometry (complex, icosahedral, and helical), host cell (bacteria, archaea, fungi, protists, plants, and animals), presence of envelope (non-enveloped or enveloped), and natural environment could also be considered. However, students could not propose any of the biochemical tests as viruses are known to be metabolically inactive. Also, viruses neither could be classified based on oxygen requirements (aerobic or anaerobic) nor motility.