Viruses

1. Viruses • have no cellular structure • not considered living • no cytoplasm, organelles, or cell membranes • do not carry out life processes • Structure of Viruses: • variety of shapes (p. 122) • consist of strands of DNA or RNA surrounded by a protective coat called a capsid (protects the virus from the host cell and helps to attach itself to receptors of the host cell).

2. Reproduction of Viruses • Before entering a cell, the virus must attach to the receptor site on the host cell. • The proteins on the surface of the virus act as keys that fit exactly into a matching shape on the host cell membrane. • The virus injects its nucleic acid into the host cell. • The host cell begins to replicate the viral DNA or RNA. • New virus particles are assembled and are released from the host cell to infect other neighboring cells.

3. Viruses Human Immunodeficiency Virus (HIV): RNA virus called a retrovirus. This type of virus causes the host cell to copy the viral RNA into DNA which is then integrated into the host cell’s chromosome. When this occurs the viral DNA is called a provirus. • Retrovirus Animation • http://www.whfreeman.com/kuby/content/anm/kb03an01.htm • HIV Animation: • http://www.sumanasinc.com/webcontent/animations/content/hiv.html