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In the light of recent classification of living organisms into three domains of life (bacteria, archaea and eukarya), which one of the following statements is true about archaea?
A
Archaea completely differ from both prokaryotes and eukaryotes
B
Archaea completely differ from prokaryotes
C
Archaea resemble eukarya in all respects
D
Archaea have some novel features that are absent in other prokaryotes and eukaryotes
Detailed Solution
Carl Woese proposed the three domain system (Bacteria, Archaea and Eukarya) on the basis of differences in 16S ribosomal RNA sequences.
Archaea are prokaryotic in organisation: they have no nucleus and no membrane-bound organelles, so they do not completely differ from prokaryotes.
They resemble eukaryotes in some features of their genetic machinery, such as histone-like proteins, RNA polymerase and the initiation of translation, but they do not resemble eukarya in all respects.
They also have some novel features of their own: membrane lipids with branched chains joined to glycerol by ether linkages, cell walls without peptidoglycan (murein), and unique pathways such as methanogenesis.
These novel features, which are absent in bacteria as well as in eukaryotes, allow them to live in extreme habitats such as hot springs, salty areas and marshy areas.
So the true statement is that archaea have some novel features that are absent in other prokaryotes and eukaryotes.
Archaea are prokaryotic in organisation: they have no nucleus and no membrane-bound organelles, so they do not completely differ from prokaryotes.
They resemble eukaryotes in some features of their genetic machinery, such as histone-like proteins, RNA polymerase and the initiation of translation, but they do not resemble eukarya in all respects.
They also have some novel features of their own: membrane lipids with branched chains joined to glycerol by ether linkages, cell walls without peptidoglycan (murein), and unique pathways such as methanogenesis.
These novel features, which are absent in bacteria as well as in eukaryotes, allow them to live in extreme habitats such as hot springs, salty areas and marshy areas.
So the true statement is that archaea have some novel features that are absent in other prokaryotes and eukaryotes.