Describe the structure of the bacteriophage virus, contrasting the way in which a bacteriophage enters a bacterium versus the way in which viruses that attack animal or plant cells enter their hosts.
Viruses that destroy bacteria, called bacteriophages, are the most complex type of virus. The protein coat of a bacteriophage has two parts: a head, which contains the nucleic acid, and a long, hollow tail, which has six fibers extending off its distal end. The tip of the tail contains a protein that reacts with receptor sites on a bacterium's cell wall, allowing the virus to bind to the cell and inject its nucleic acid. Viruses that attack animal and plant cells, in contrast, often enter the cell completely. Once the virus is inside the host, the host's own enzymes digest the protein coat, freeing the virus's nucleic acid to begin replicating itself.
