AIDS is an interesting virus. But I suspect that there are many other interesting virri out there, I just happen to know a little bit more about AIDS than the others, since it is so much in the spotlight. Virri in general are intriguing, and well worth a little study by anybody who finds science interesting. What follows attempts to prove that AIDS is chaotic, something which I agree with, but have a hard time explaining in words. Read it anyway for a quick overview of both subjects. You may just find yourself wanting to find out more!
The AIDS virus is very resistant to attacks from the human immune system. One of the reasons for this is a by-product of the method of replication used by HIV. HIV is a retrovirus, which means that its genetic code is stored as RNA. After this RNA is injected into a cell, it must be converted to DNA, so that it may then be integrated in the host's DNA. Unfortunately for the host, the process of converting RNA to DNA is inherently prone to miscopying, and on average the resulting DNA code is different by one base pair. When the new DNA is used as a blueprint to produce the virus, some of the resulting HIV molecules are not viable. However, those that have a mutation in a non-crucial area, such as the surface proteins, survive, with an important advantage. These surface proteins are the target of the antibody mediated immune response, which only works well against non-changing antigens to which it has been exposed for a long period of time. Thus the rapid mutation of surface proteins renders ineffective a major immune avenue of attack.
Chaotic systems change in cyclic patterns, with each cycle always somewhat different from the previous cycle. Small changes in a system early on can make large differences later. Often it is hard to see any pattern in chaos unless the entire system is examined for a long period of time. A simple example of chaos is the shoreline of a river. Just about any part of the shore looks very much like any other part, but no two areas are exactly alike. Small, but long lasting changes in currents upstream will make larger and larger differences downstream. This is because the direction of flow at any point is strongly influenced by the direction of water flow just above it. Over long periods of time, the path of the river will change, producing a recognizable pattern that will never be exactly the same twice.
I believe the mutating protein coat of HIV is an example of chaos. The proteins do not change completely, since they remain functional, yet they do change enough to evade the immune system. The changes are not very large between generations, and over time the proteins maintain the same basic pattern, since the radically different structures that arise do not survive. These mutations may seem basically random, but when considered in the context of the entire system, they produce a reoccurring pattern of the body getting ready to battle a virus, only to have that virus effectively become invisible.
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