title: Archaebacteria.
abstract: Experimental work published elsewhere has shown that the Archaebacteria encompass several distinct subgroups including methanogens, extreme halophiles, and various thermoacidophiles. The common characteristics of Archaebacteria known to date are these: (1) the presence of characteristic tRNAs and ribosomal RNAs; (2) the absence of peptidoglycan cell walls, with in many cases, replacement by a largely proteinaceous coat; (3) the occurrence of ether linked lipids built from phytanyl chains and (4) in all cases known so far, their occurrence only in unusual habitats. These organisms contain a number of 'eucaryotic features' in addition to their many bacterial attributes. This is interpreted as a strong indication that the Archaebacteria, while not actually eucaryotic, do indeed represents a third separate, line of descent as originally proposed.
mesh_terms: D001419:Bacteria / Q000145:classification / Q000235:genetics*; D002473:Cell Wall / Q000032:analysis; D005057:Eukaryotic Cells / Q000502:physiology; D019605:Euryarchaeota / Q000032:analysis / Q000145:classification / Q000235:genetics*; D008055:Lipids / Q000032:analysis; D010802:Phylogeny; D014176:Protein Biosynthesis
chemical_list: D008055:Lipids