Chapter 1.1, Problem 1CSC

The Boundaries of Life

Are viruses alive? Viruses release their genetic material inside cells and then hijack the infected cell's energy supplies and biochemical machinery, turning the cell into a kind of factory that chums out many copies of viral parts. These parts assemble into an army of virus particles. The newly formed viruses then emerge from the host cell, often rupturing it in the process. Some types of viruses, including HIV and the Ebola virus, acquire an outer envelope made of the infected cell's plasma membrane as they emerge. Viruses do not obtain or use their own energy or materials, maintain themselves, or grow. Therefore, viruses do not meet our criteria for life. They do, however, possess a few characteristics of life: Viruses respond to stimuli by binding to specific sites on the cells they attack, and some scientists consider viral replication a form of reproduction. Viruses also evolve, often with stunning speed. How does evolution occur in viruses and other biological entities?