BIOLOGY Volume 1 - A Guide to General Biology - 2004

2. THE DIVERSITY OF LIFE ON EARTH

2.4. Viruses

2.4.5. Structure and Life Cycle of a Retrovirus: The Example of HIV

AIDS (Acquired Immunodeficiency Syndrome) is of particular interest among viral diseases because it is a relatively new condition, first reported in the USA in 1981. AIDS is caused by the HUMAN IMMUNODEFICIENCY VIRUS, commonly abbreviated as HIV. Interest in this virus is also due to the fact that HIV belongs to a group of Viruses known as Retroviruses—a name reflecting a unique feature of their Replication. Normally, the flow of Genetic information proceeds in the direction DNA → RNA, meaning that information encoded in a specific DNA segment (a Gene) is transcribed into a corresponding RNA molecule. In contrast, retroviruses, which use RNA as their inherited genetic material, undergo reverse METABOLISM/31.html">Transcription, meaning that genetic information is transferred in the opposite direction: from RNA to DNA. The enzyme responsible for this reverse transcription is called Reverse Transcriptase. It is widely used in Introduction/32.html">Genetic Engineering (Ch. 25).

Figure 2.21 illustrates The Structure of HIV, and Figure 2.23 diagrams its life cycle (see also Fig. 2.24). HIV infects and destroys a specific group of white Blood Cells known as T-helper lymphocytes, thereby suppressing The Immune System. The disease caused by this virus (AIDS) is discussed in Chapter 15.

Class="center">

Fig. 2.23. Life Cycle of the human immunodeficiency virus (HIV).

Fig. 2.24. HIV budding from an infected Cell.