Comparisons of Eubacteria, Archaea, and Eukaryotes
Characteristic | Eubacteria | Archaea | |
Cell wall | gram +ve or gram -ve (structure) | murein absent | plasma membrane |
Predominantly multicellular | no | no | yes |
Nucleus, membrane bound organelles | no | no | yes |
DNA | circular | circular | linear |
Ribosome | 70s | 70s | 80s |
Membrane lipids ester-linked* | yes | no | yes |
Photosynthesis with chlorophyll | yes | no | yes |
Growth above 80o C | yes | yes | no |
Histone proteins present | no | yes | yes |
tRNA initiator | fMet | Met | Met |
Operons | yes | yes | no |
Introns in genome | none | some [a, 1, 2, 3, 4, 5, 6, 7, 8,] | most |
Capping and poly-A tailing of mRNA | no | no | yes |
Transcription factors required | yes | no | yes |
Methanogenesis | no | yes | no |
Nitrification | yes | no | no |
Denitrification | yes | yes | no |
Nitrogen Fixation | yes | yes | no |
Chemolithotrophy | yes | yes | no |
Gas vesicles present | yes | yes | no |
Sensitive to chloramphenicol, kanamycin and streptomycin | yes | no | no |
* Archaea membrane lipids are ether-linked | |||
Adapted from here. |
Property | Eubacteria | Archaea | Eukarya |
Cytological features | |||
Nucleus | No | No | Yes |
Cytoskeleton | No | No | Yes |
Organelles (mitochondria, chloroplasts, Golgi apparatus, endoplasmic reticulum) | No | No | Yes |
Molecular features | |||
DNA topology | Negatively supercoiled | Relaxed or positively supercoiled (in hyperthermophilic Archaea that contain reverse gyrase) | Negatively supercoiled |
Promoter structure | Two conserved boxes at - 10 (TATAAT) and - 35 (TTGACA) from transcription start site | TATA box and/or initiator element | TATA box and/or initiator element |
RNA polymerase | One type; relatively simple subunit composition; binds directly to promoter (can be footprinted) | One type; complex subunit structure (subunit pattern, genes, and serological properties similar to eukaryal RNA polymerase II); can be footprinted, but still requires basal transcription factors for promoter recognition [1, 2, 3,] | Three types; complex subunit compositions; cannot be footprinted; require basal transcription factors for promoter recognition/binding |
Basal transcription factors | No | TBP , TFIIB, and TIIS homologs of eucaryal RNA polymerase II-associated factors described thus far | TBP, TAFs, TFIIA, TFIIB, TFIIE, TFIIF, TFIIH required for RNA polymerase II initiation; P-TEFb, TFIIS, TFIIF, elongin, and ELL required for elongation |
Poly(A) tails in RNA | Short | Short (avg. 12 bases in length) | Long |
Chromatin | No | ? | Yes |
Table adapted from Archaeal chromatin: Virtual or real? Jordanka Zlatanova Proc. Natl. Acad. Sci. USA, Vol. 94, pp. 12251-12254, November 1997
For further features and references see the series of minireviews on Archaea published in the June 27, 1997, issue of Cell, and refs. 5 and 27.
Cell walls of Prokaryotes Electron acceptors for respiration and methanogenesis in prokaryotes Glycolysis in bacteria Lithotrophic prokaryotes Gene Regulation in E.coli Second Messengers Cell signaling
Cell walls of Prokaryotes
Domain | Eubacteria | Archaea |
membrane | Glycerol-ester lipids | Glycerol-ether lipids |
lipids | Amphipathic molecules containing a backbone of glycerol connected to a hydrophilic head group and two hydrophobic long-chain fatty acids. Fatty acids are attached to the glycerol backbone by ester bonds. |
Isoprenoid side chain Fatty acids are attached to the glycerol backbone by ether bonds. In some extremophiles, C-40 hydrophobic chains attached to the glycerol backbone are twice normal length and pass completely through the membrane, attaching to a second backbone on the opposite side and adding stability. |
chains | linear | branched carbon rings |
chirality of glycerol | D-glycerol (R) | L-glycerol (S) |
lacking cell wall | Mycoplasma (sterol-like compounds in cell membranes provide osmotic protection) |
Thermoplasma, Picrophilaceae |
In addition to differences in composition of the cell membrane, Eubacteria and Archaea differ in the composition of the cell wall. Cell walls are rigid to semi-rigid structures that enclose the protoplastic cell membrane, and which are found in bacteria, archaea, fungi, plants, and algae, but not in animals.
Comparisons of Eubacteria, Archaea, and Eukaryotes
Cell Wall | Gram +ve bacteria | Gram -ve bacteria |
Gram +ve Archea | Gram -ve Archaea |
outer membrane | Lipoprotein-lipopolysaccharide-phospholipid (LPS) with porins. Braun’s lipoprotein anchors outer membrane to peptidoglycan |
|||
peptidoglycan* |
thick teichoic acid |
none | none pseudomurein or complex carbohydrate |
none protein-glycoprotein |
S-layer patterned, surface layer of protein or glycoprotein |
some bacteria associated with the peptidoglycan |
some bacteria adheres directly to outer membrane sole cell-wall component in Planctomyces |
commonly constitutes cell wall | commonly constitutes cell wall |
*Peptidoglycan comprises N-acetylglucosamine (NAG) bonded to N-acetyl muramic acid (NAM) by a 1,4 glycosidic bond. The N-acetylmuramic acid (NAM) in peptidoglycan is replaced by N-acetyl talosaminouronic acid acid (NAT) in pseudopeptidoglycan (pseudomurein) of Archaea (im). Each glycan is linked by 1,4 glycosidic bonds in peptidoglycan and by 1,3 glycosidic bonds in pseudomurein (NAT). Hyperthermophiles use branched glycerol tetraethers (single-layer membranes) to increase membrane fluidity, so they lack a cell wall. Psychrophiles have plasma membranes with lipids that contain mainly unsaturated fatty acids.
Electron acceptors for respiration and methanogenesis in prokaryotes
Electron acceptor | Reduced end product | Process | Organism |
O2 | H2O | aerobic respiration | Escherichia, Streptomyces |
NO3 | NO2, NH3 or N2 | denitrification | Bacillus, Pseudomonas |
SO4 | S or H2S | sulfate reduction | Desulfovibrio |
fumarate | succinate | anaerobic respiration
using an e- acceptor |
Escherichia |
CO2 | CH4 | methanogenesis | Methanococcus |
Glycolysis in bacteria
Bacterium | Embden-Meyerhof pathway | Phosphoketolase (heterolactic) pathway | Entner-Doudoroff pathway |
Acetobacter aceti | absent | present | absent |
Agrobacterium tumefaciens | absent | absent | present |
Azotobacter vinelandii | absent | absent | present |
Bacillus subtilis | major | minor | absent |
Escherichia coli | present | absent | absent |
Lactobacillus acidophilus | present | absent | absent |
Leuconostoc mesenteroides | absent | present | absent |
Pseudomonas aeruginosa | absent | absent | present |
Vibrio cholerae | minor | absent | major |
Zymomonas mobilis | absent | absent | present |
Lithotrophic prokaryotes
Physiological group | Energy source | Oxidized end product | Lithotrophic organism |
methanogens | H2 | H2O | Methanobacterium |
hydrogen bacteria | H2 | H2O | Alcaligenes, Pseudomonas |
carboxydobacteria | CO | CO2 | Rhodospirillum, Azotobacter |
nitrifying bacteria* | NH3 | NO2 | Nitrosomonas |
nitrifying bacteria* | NO2 | NO3 | Nitrobacter |
sulfur oxidizers | H2S or S | SO4 | Thiobacillus, Sulfolobus |
iron bacteria | Fe ++ | Fe+++ | Gallionella, Thiobacillus |