2. Viruses were discovered when scientists passed fluid from infected organisms through filters that held back bacteria, and then demonstrated that the strained material was infectious.
3. A virus's protein coat is a capsid; the viral particle outside a cell is a virion. Capsids have a variety of shapes.
4. A viral envelope includes virally encoded proteins and lipids, some of which may have come from host cell membranes.
19.2 Viruses Infect Cells to Reproduce
5. A virus binds to a surface molecule on a host cell, then injects its nucleic acid or is engulfed. Insects assist viruses in infecting plant cells. The viruses then spread via plasmodesmata that link plant cells.
6. In a lytic infection, progeny virions are manufactured, assembled, and released. In a lysogenic infection, the bacteriophage nucleic acid integrates into the host DNA and remains hidden. Some animal viruses can exist hidden within a host cell in a latent infection.