What are the common Characteristics of the Archaea Domain?
There are a large number of basic characteristics that Archaeans share with other organisms. The characteristics that Archaeans share with Bacteria are as follows: a circular genome (the nucleic acids that contain the genetic information is circular), genes are groups in operons, mRNA is polycistronic, there is no RNA processing performed by Archaeans or Bacteria, there are no introns found within the genetic material, similar cell size, no nucleus or membrane bound organelles. The characteristics that Archaeans share with Eukarya are as follows: no peptidoglycan in the cell membrane or cell wall, DNA is associated with histone proteins, translation is initiated using methionine, they share similar transcriptional processes (use of promoters, use of RNA polymerase, etc), there are similarities in the replication and repair of DNA, and they share a similar ATPase (that ATPase being Type V).
In addition to characteristics that are shared with other organisms, Archaeans also have their own unique characteristics that set them apart. The cell wall structure of Archaeans is unique. Their cell walls contain pseudomurein (as opposed to the peptidoglycan that is found in the cell walls of bacteria). The cell membrane contains ether-linked lipids. This is unique to Archaeans as well. The protein structure of flagellin that is used by Archaeans for motility is unique as well. Though some of the characteristics of ribosomal structure are shared with both Bacteria and Eukarya, there are notable differences in Archaean ribosomal structure. In addition to the aforementioned unique characteristics, Archaeans have no fatty acid synthetase enzyme.
The cellular membranes of Archaeans significantly differ from those of other organisms. The phospholipid composition of the cell membrane in Archaean cell membranes are unique in a number of ways. Archaean cell membranes are primarily composed of glycerol-ether lipids rather than glycerol-ester lipids. Ether bonds are more chemically resistant than ester bonds, which allows Archaean cell membranes to hold up under the harsh conditions of the environments in which they live. The glycerol moiety stereochemistry is reversed from that which is found in the cell membranes of other organisms. Lipid tails in Archaean membranes are also different. They often contain multiple-side branches and can even contain aromatic rings. Some Archaean membranes are monolayers rather than bilayers.
The metabolism of Archaeans is similar to that of other organisms. Phototrophs use sunlight and organic compounds for their metabolism. Lithotrophs use inorganic compounds and organic compounds for metabolism. Organotrophs use organic compounds for both their energy source and their carbon source in their metabolism. Archaeans can use many carbon compounds for their metabolism and are sometimes involved in the process of carbon fixation using a modified form of the Calvin cycle.
One of the most unique characteristics of Archaeans is the environment in which they live. They are found in a very wide range of habitats. Archaeans are often found living where no other life can survive. These Archaeans are known as extremophiles and they come in four main varieties: thermophiles, acidophiles, alkaliphiles, and halophiles. Halophiles are capable of living in extreme saline environments. Examples of environments in which halophiles can life are salt lakes. Thermophiles are capable of surviving at very high temperatures and often grow in thermal vents or hot springs. Acidophiles and alkaliphiles survive in very acidic or very basic environments, respectively. It is the ability to survive in these extreme environments that helps to set Archaeans apart from other domains of life.
Written By: Alexander Maness, United States (M.S. in Biotechnology)
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Edited by: Rajesh Bihani ( Find me on Google+ )