|
Procaryotes are one-celled organisms whose cells lack a true
(membrane-bounded) nucleus and other eucaryotic organelles.
Procaryotes include the Archaebacteria, true bacteria, and Cyanobacteria.
Procaryotic cells: Cells without true nuclei, lacking many other structures found in eucaryotic cells. Procaryotic cell walls: Contain substances like muramic acid, absent in eucaryotes. Chemical diversity: Procaryotes have greater chemical diversity than eucaryotes. They can subsist on a greater variety of foodstuffs, have a greater range of chemical substances that can be tolerated, and can subsyst in a variety of atmospheres, both with and without oxygen. Procarytoic chromosomes: Generally arranged in a single circular loop containing DNA byt no histone proteins. Partial recombination may occur during conjugation. Most procaryotes also have small chromosome fragments that can detach from the main chromosome and exist separately for long periods as plasmids, small, circular samples of DNA similar to certain viruses. Archaea (Archaebacteria): A group of strict anaerobes (killed by oxygen) that include the methane-producers (methanogens), the extreme halophiles, and the extreme thermophiles. Their RNA sequences have only minimal homology to the RNA of other procaryotic or eucaryotic organisms, and the cell walls are also unique. True bacteria: The majority of procaryotes, with RNA sequences homologous to those of Cyanobacteria and eucaryotes (but not Archaebacteria). Most are heterotrophs. A few autotrophs use a variety of energy sources, but none contains chlorophyll a and none can split water in the Hill reaction. Cyanobacteria (= Cyanophyta, blue-green bacteria, or blue-green algae): All are similar to bacteria in structure and their RNA sequences are homologous. All are oxygen-tolerant autotrophs that can use sunlight for energy and CO2 as a carbon source. They contain chlorophyll a and can split water in the Hill reaction. |
| Prev | rev. Aug. 2011 | Next |