It is hypothesized that archaeans are the origin of life. They are organisms that exist in extreme environmental conditions like those of the early Earth, such as in areas of high concentrations of methane and ammonia, as well as those of extreme temperatures of hot or cold. They share genes with both bacteria and eukaryotes, but also have genes that are completely unique to archaeans.
Archaea and Bacteria are Similar Prokaryotic Cells
Like bacteria, archaea are single-celled organisms and are generally rod-, sphere-, or spiral-shaped. They may have hair-like flagella that are used to propel the organism. One or many flagella may be present, although they are usually located on one side of the organism when many are attached. They are prokaryotic because they do not have a nuclear membrane, so their DNA is clumped within the cell and is known as a nucleoid.
They look like bacteria and function in many of the same ways, but are quite different in other ways. The archaean cell membrane is the structure that significantly distinguishes archaea from bacteria and eukaryotes. The membrane consists of two layers of glycerol that structurally differ from bacterial and eukaryotic membranes in such a way that it looks like a mirror image of those membranes, such as with a right hand and a left hand.
Optical Isomers or Enantiomers
The two hands look the same and have the same parts attached in the same order, but differ so that a fitted right glove will not properly fit a left hand. If the right glove is placed on the left hand, the knuckles for the glove will actually be placed on the palm of the left hand. This is important because chemical reactions rely on chemicals fitting together perfectly, like a right hand fitting into a glove that is clearly designed for a right hand. These mirror-image-like molecules are classified as the right (D) and left (L) isomers.
Archaea Have Cell Walls Containing the Isomer L-glycerol
The archaean cell wall consists of a chain of molecules comprised of a phosphate group, L-glycerol, an ether linkage, and branched isoprene chains, respectively. Bacterial and prokaryotic cell walls contain the following respective molecules: a phosphate group, D-glycerol, an ester linkage, and unbranched fatty acids.
Since the archaean isoprene chains are branched, they can connect to each other and can be referred to as transmembrane phospholipids. They can also form carbon rings. According to the article, "Archaea: Morphology," (accessed April 26, 2010) by Ben Waggoner of the Department of Biology at the University of Central Arkansas, and Brian R. Speer of the University of California in Berkeley, "This happens when one of the side branches curls...and bonds with another atom down the chain to make a ring of five carbon atoms. Such rings are thought to provide structural stability to the membrane, since they seem to be more common among species that live at high temperatures."
Structurally, archaea look like close relatives of bacteria, and both are prokaryotes; however, differences in the cell walls are not the only reason for putting archaea in their own domain. Genetically, archaea are much more similar to eukaryotes, which consist of animals, fungi, plants, and protists.
Diane Ursu - Diane Ursu joined Suite101 as a contributing writer in August 2009 and became a Feature Writer in January 2010. She is a freelance writer ...
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