Animal VirusesAnimal viruses are very diverse in their size and structure, and the exact nature of their genetic material, which can be double or single stranded RNA or DNA. We will consider the Human Immunodeficiency Virus (HIV) as an example of an animal virus.
The first stage of HIV infection involves attachment of the virus to the host cell. HIV has proteins on its outer membrane that recognize a specific protein (the receptor) on the host cell. After docking to the receptor, the virus enters the cell via endocytosis (see Chapter 11).
Some RNA viruses, such as HIV, must have their RNA copied into DNA for the cell to use it (these viruses are called retroviruses). This is accomplished by the viral enzyme reverse transcriptase. The DNA copy is made in the cytoplasm of the host cell and is then transported into the nucleus, where it can incorporate with the host DNA (the virus is now called a provirus, analogous to a prophage). Newly synthesized viral particles can be released via exocitosis. Therefore, the virus does not always kill the host cell.
Structure of HIV