Archaeans

Also referred to as Archaea, the smaller set on non-nucleated cellular life that used to be referred to as bacteria or prokaroytes. Considered one of the three major types of cellular life. They differ biochemically in the arrangement of the bases in their ribosomal RNA and in the composition of their plasma membranes and cell walls from the Eubacteria. Often regarded as extremophiles, with tendencies to methanogens, halophiles, and thermophiles. The methanogens are anaerobic bacteria that produce methane. They are found in sewage treatment plants, bogs, and the intestinal tracts of ruminants. Ancient methanogens are the source of natural gas. Halophiles are bacteria that thrive in high salt concentrations such as those found in salt lakes or pools of sea water. Thermophiles are the heat-loving bacteria found near hydrothermal vents and hot springs. Many thermophiles are chemosynthetic using dissolved sulfur or other elements as their energy source and iron as a means of respiration. Archaebacteria emerged at least 3.5 billion years ago and live in environments that resemble conditions existing when the earth was young. Arachae have pseudopeptidoglycan cell walls, lipids are branched chain hydrocarbons linked to glycerol molecules by ether linkages - fatty acid components are not found in archeal lipids, DNA in a single circular molecule but with extrachromosal plasmids, histone-like DNA binding proteins, complex (up to 14 subunits) RNA polymerases, high internal salt concentrations.