Archaea, previously named Archaebacteria, is a superkingdom consisting of bacteria like single cellular organisms which are found in extreme environments like harsh spring, salts lakes as well as normal environment.
Before their molecular structure was studied they were kept under bacteria as a subgroup.
Now, when it was found that they are made of different structural molecules, they are not put inside eukaryotes or prokaryotes, a complete different domain had to create for the group.
Let us see what was found:
In single cellular organisms like prokaryote and eukaryote, the cell membrane consists of phospholipid bilayer. This phospholipid molecules are made of saturated and unsaturated long chain fatty acids bound to phosphatidic acid by ester bonds, ie, by -COO-
But, molecular analysis revealed that phospholipid of Archea contains phospholipids made of isoprenyl alephatic side chains bound to phosphatidic acid by ether bonds, ie, by -O-; giving much resilience to the membrane making it capable of living in harsh environments as it was mentioned above.
Now, scientists realized it would require a completely different set of enzymes to build such membrane. They analyzed and found so. The enzymes are nor like that of bacteria’s neither that of eukaryots’.
So, finally, Archaebacteria consisting of a whole lot of species was grouped under a different Domain named Archaea.
Presently, there are three domains in cellular organisms, namely, Archea, Prokaryot and Eukaryote.
What is interesting to note here is, Archaebacteria was previously thought to be evolved from Bacteria; but now they have to find another common ancestor from which the Bacteria, Archaea and Protozoa has come.
And you see, this process will go on. If a new domain is discovered in future, they will also put that domain aside the previous three and try to find a common ancestor. Because the goal of the Evolutionists is to find a common ancestor, even if possible to find it in their IMAGINATION.
[The article was previously posted here: http://www.sonarbangladesh.com/blog/abdullahdmc/68030]