ABSTRACT

In Chapter 27, some of the smallest genomes were discussed. The RNA viruses have only a few genes, but can infect more complex cells and utilize parts of those cells to produce more viruses. On average, DNA viruses are larger than RNA viruses (Figure 27.1), but they are also parasites that take over the host cell to produce more virus particles. However, viruses can be more than parasites. They are vital in some environments. In parts of the oceans, nutrient levels are extremely limiting, and therefore, few organisms can survive. However, viruses make it possible for a diverse set of organisms, especially microbes, to live. When the viruses infect cells, many of them lyse the host cell as a way to release the newly constructed virus particles. In doing so, they also release all of the organic contents of those cells. These organics become valuable sources of nutrients for the other organisms in the vicinity. Therefore, viruses are important components of nutrient cycling in the oceans and in other environments where nutrient levels are low.