E-Z Microbiology by Rene Kratz

Author:Rene Kratz
Language: eng
Format: epub
Publisher: Barrons Educational Series
Published: 2011-04-02T16:00:00+00:00

REMEMBER

Animal viruses enter host cells by endocytosis or fusion.

In addition to demonstrating the same two basic patterns of infection as bacteriophage, animal cell viruses also demonstrate the same basic steps of viral multiplication. Essentially, all viruses must do attachment, penetration, biosynthesis, maturation, and release. However, many viruses that infect animal cells are enveloped viruses, and this affects the way some of these steps are done. After an enveloped virus has attached to a host cell, penetration occurs by fusion (Figure 13.5.1) or endocytosis (Figure 13.5.2). In endocytosis, the host cell surrounds the virus with plasma membrane and brings it into the cell in a vesicle. In fusion, the viral envelope becomes part of the plasma membrane of the host cell. Both endocytosis and fusion result in the viral capsid entering the host cell along with the viral genetic material. In order for viral multiplication to begin, the capsid must be removed. This is called uncoating, and it may be accomplished by viral or host enzymes, depending on the virus. Finally, enveloped viruses must pick up a new envelope as they exit the cell. During biosynthesis, viral proteins are inserted into the plasma membrane of the cell. After the virions are assembled during maturation, budding (Figure 13.6) occurs. During budding, the virions push out through the modified plasma membrane and are wrapped in a new envelope as they exit the cell.

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