Genetics3



Evolution and Genetic Engineering
Activity 1:
Why is AIDS so difficult to cure? How does the AIDS virus attack the body?
à In 1979, the first reported AIDS case occurred in New York, and by mid-June 1981, unusual immune system failure among gay men was surfacing in the United States. The Centers for Disease Control (CDC) initially name the disease GRID, or gay-related immune deficiency, because it was prominently found among homosexuals. It appeared to be a lifestyle-associated illness, linked to excessive stress to the immune system. Researchers believed that a highly infectious agent, which depleted T cells and could be transmitted through intercourse, blood, or blood products from mother to fetus, caused GRID. In July of 1982, the disease was renamed AIDS, or Acquired Immune Deficiency Syndrome. Since then, the disease’s origins, the factors affecting it, the causes behind it, the symptoms arising from it, the groups at risk from it, and the practices leading to it have been widely and comprehensively researched. Despite painstaking efforts and billions of dollars spent on research, despite the numerous drugs created to control and relieve its various symptoms, there is still no cure for it. We ask the question, “Why?”.

AIDS is caused by the human immunodeficiency virus, or HIV. HIV’s coat of protein fits the receptors in certain types of white blood cells (T cells) in the human immune system. When the virus is taken into these cells, it reproduces and destroys the immune system cell in the process. It attacks the body by attacking the immune system, making the person susceptible to and defenseless against many infections that he or she would normally be able to fight off easily. In many cases, HIV infection leads to AIDS, which ultimately leads to death.
HIV is a retrovirus that is transmitted by the exchange of bodily fluids -- usually through sexual acts and the sharing of drug needles, mother to infant transmission, and sometimes by the contamination of blood used in transfusions. A retrovirus is a type of virus that contains RNA and produces a DNA analog (or counterpart) of its RNA by using a highly error-prone enzyme known as reverse transcriptase. The virus is a complex one, with two coats of protein. The outer coating fits with the receptors of T cells and the inner coating contains strands of RNA along with a few different types of enzymes. Once the virus is taken into the cell, an enzyme makes reverse transcription take place, which turns the virus’ RNA into a corresponding set of DNA, which contains nine genes. A second set of enzymes insert the genes into the cell’s DNA, making the cell produce protein and RNA needed to make more viruses (we can see how the virus uses the human cell for reproduce), and the third set of enzymes makes these raw materials into new viruses and moves them out of the cell membrane. These then go on to infect other cells, and the process is repeated again and again, infecting the human body.
The reason why AIDS is difficult to cure is because, as mentioned above, the copying process is error-prone, or sloppy. Usually, when DNA is replicated in a cell, there is constant proofreading and repair to ensure that the correct type of DNA is being made. In the case of the AIDS virus, in the process of reverse transcription, there is no proofreading mechanism. This makes DNA made from the viral RNA very different from what is coded therein. As a result, every virus that is produced is slightly (but significantly!) different from the one that produced it. This makes it hard for scientist to find a cure because the virus continuously mutates, making drugs that fit onto one kind of HIV ineffective against the others. However, there is hope for AIDS victims in the sense that scientists in the future will be able to make several drugs, which will be taken in combination. These drugs will then act upon the virus by blocking its life cycle at various points, making the disease manageable, at the least.
Since it began, the HIV/AIDS epidemic has claimed the lives of 21.8 million people, and, up to date, has its grasp on 36.1 million people. This is a very large amount, and considering the fact that there exist many more