VIRUSES. Virus. A particle composed of nucleic acid, protein, and in some cases lipids that can reproduce only by infecting living cells. The term, virus, comes from the Latin word for poison. Most viruses are highly specific to the cells they infect. Structure of Viruses.
Retroviruses—contain RNA as their genetic information. Get their name from the fact that the genetic information is copied backwards. HIV (human immunodeficiency virus) is a retrovirus.
Prions—contain no DNA, just protein. Prion means, “protein infectious particles”. Diseases such as mad cow disease (cows), scrapie (sheep and goats), and kuru (humans) may be caused by these.
Methanogens—produce methane gas in oxygen free environments. Found in marshes, lake sediments, and in the digestive tracts of some mammals, such as cows.
Extreme halophiles—live in water with high salt concentrations.
Thermoacidophiles—live in extremely hot water such as hot springs and deep ocean vents.
Binary fission—asexual splitting in two (some may divide every 15 minutes)
Conjugation—sexual recombination of DNA