The Structure of Bacteria and Molecular Biology of Viruses

The design of prokaryotes has been a tremendously successful feature of their existence. Even today, bacteria and viruses remain one of the most successful life forms and are among the most abundant. Unlike some eukaryotic cells, bacteria are not able to engulf particulate foodstuffs. Instead, they must rely entirely on diffusion. Bacteria come in many shapes and forms; they can be spherical, rod-like, spiral, filamentous, comma-like, square, or ring-like. One of the primary functions of these various designs is to increase the surface area to volume relationship; the greater the surface area, the greater the likelihood of encountering a diffusing substrate. Receptor proteins, transport proteins, and specialized pores must also contribute to ingestion, but it is the overall cellular design that provides a fundamental advantage. The structure of viruses reflects their association with the extracellular and intracellular environment. In its extracellular environment, viruses are in the form of mature virions that are capable of protecting their sensitive genomes and transmitting their genetic information to new susceptible cells. In its intracellular environment, the protective coat is no longer needed and the virus structure changes. The mature virus structure allows survival in the extracellular environment and specific association with cells.