What is the Three-Domain System?
The three-domain system is a classification of cellular life forms proposed by Carl Woese in 1977. It divides prokaryotes into two categories, which were initially called Eubacteria and Archaebacteria. Based on the differences in 16S rRNA sequences, Woese believes that these two types of organisms and eukaryotes have evolved from a common ancestor with a primitive genetic mechanism. Therefore, each of the three types is set as a "Domain" as a comparison The "world" is a higher-level classification system, and is named as Bacteria, Archaea, and Eukarya.
Three domain system
Based on the differences in 16S rRNA sequences, Woese believes that these two groups of organisms and eukaryotes have evolved from a common ancestor with a primitive genetic mechanism, so they are classified into one category as a higher-level classification system. Called "Domain" or "Superkingdom." In 1990, Carl Woese tried to avoid
Three-domain feature comparison | feature | Bacteria | Archaea | Eukarya |
|---|
Morphology and heredity | Prokaryotic cell structure | Yes | Yes | no |
Covalently closed circular DNA | Yes | Yes | no |
Histone | no | Have | Have |
Enveloped core | no | no | Have |
Cell wall | Cellular acid | Free of cellular acids | Free of cellular acids |
Membrane lipid | Ester linkage | Ether linkage | Ester linkage |
Ribosome size | 70S | 70S | 80S |
Start tRNA | Formylmethionine | Methionine | Methionine |
Introns in most genes | no | no | Yes |
Operon | Have | Have | no |
mRNA capped and poly A tail | no | no | Have |
Plasmid | Have | Have | rare |
Ribosome is sensitive to diphtheria toxin | no | Yes | Yes |
RNA polymerase | 1 (4 subunits) | Several (each 8 ~ 12 subunits) | 3 (12 ~ 14 subunits each) |
Requires transcription factor | no | Yes | Yes |
Promoter structure | -10 and -35 sequences | TATA box | TATA box |
physiological | Methanogenesis | no | Have | no |
Nitrification | Have | no | no |
Denitrification | Have | Have | no |
Nitrogen fixation | Have | Have | no |
Photosynthesis based on chlorophyll | Have | no | Yes (in the chloroplast) |
Rhodopsin-based energy metabolism | Have | Have | no |
Chemoenergy Inorganic Nutrition (Fe, S, H2) | Have | Have | no |
bubble | Have | Have | no |
Poly--hydroxy fatty acids as carbon storage particles | Have | Have | no |
Grow above 80 | Have | Have | no |
