The Biology of The Human Immunodeficiency Virus
A virus is a tiny, relatively simple, nonliving organism, usually made up of little more than a few strands of genetic material and a protein shell. HIV is a virus that infects only people and creates a deficiency in their body's immune system. How does HIV evade the immune system so efficiently? Why are so many variants of the virus found in a single patient? Understanding the structure and life cycle of the virus is key to answering these questions.
HIV belongs to a family of viruses called retroviruses. Unlike regular viruses, which have DNA (deoxyribonucleic acid) as their genetic material, HIV (human immunodeﬁciency virus) is composed of two strands of RNA, 15 types of viral proteins, and a few proteins from the last host cell it infected, all surrounded by a lipid bilayer membrane. Together, these molecules allow the virus to infect cells of the immune system and force them to build new copies of the virus. Each molecule in the virus plays a role in this process, from the ﬁrst steps of viral attachment to the ﬁnal process of budding. 25 years of research on the structural biology of HIV have revealed the atomic details of these proteins. Using these data, researchers have designed new treatments for HIV infection, including effective drug regimens that halt the growth of the virus. The structures also provide new hope for development of a vaccine.
Although deadly to the cell it attacks, a single human immunodeficiency virus (or viral particle) is much smaller than a human cell. HIV particles have a diameter of only 1/10,000 of a millimeter, compared to the average human cell size of 1/10 of a millimeter. HIV particles are also much simpler in structure than human cells. HIV particles are made up of the following parts:
The outer coat of the virus is called the viral envelope or lipid membrane. The viral envelope is composed of two layers of fat molecules. HIV gets its outer envelope from its host. As...