The Archaea are presently recognized as one of the two main domains of prokaryotes. The majority of genes that indicate Archaea to be different from Bacteria are for information transfer processes such as DNA replication, transcription and translation. Of these, DNA replication machinery appears to be most different between the two domains. In terms of transcription, the core subunits of the RNA polymerase are the same in Bacteria and Archaea, but archaea also contains several smaller subunits as well as certain transcription factors not found in bacteria. Most components of the translation machinery which includes different rRNAs, r-proteins, major elongation factors, various amino acid-charging enzymes and tRNAs, etc. are generally common to both Bacteria and Archaea. Further, the r-proteins in Archaea are also arranged in operons similar to that seen in Bacteria (Bacterial, 2006).
However, apart from these differences, Archaea are extensively similar to Bacteria. Most of the metabolic pathways, which comprise the vast majority of any organism’s gene repertoire, are common between Archaea and Bacteria. In terms of their cell structures, Archaea are indistinguishable from Gram-positive bacteria. Within prokaryotes, only these two groups of organisms are bounded by a single unit lipid membrane, and they generally contain a thick sacculus of varying chemical composition. Some Archaea also show positive Gram staining and a few of them, similar to certain Gram-positive bacteria, do not contain any cell wall (Bacterial, 2006).
The similarity between Archaea and Bacteria extends to numerous other characteristics including, their cellular size which is much smaller than that of eukaryotic cells, absence of nucleus, cytoskeleton, histones, spliceosomal introns, circular organization of their genomes, organization of genes into operons (Bacterial, 2006).
The domain Archaea, like Bacteria, includes prokaryotes. Although they look superficially...