PROKARYOTES Prokaryotes (pro-KAR-ee-ot-es) (from Old Greek pro- before + karyon nut or kernel, referring to the cell nucleus, + suffix -otos, pl. -otes; also spelled "procaryotes") are organisms without a cell nucleus (= karyon), or any other membrane-bound organelles. Most are unicellular, but some prokaryotes are multicellular). Contents 1 Relationship to eukaryotes 2 Genes 3 Colonies 4 Structure 5 Environment 6 Evolution of prokaryotes 7 References 8 See also 9 External links Relationship to eukaryotes A major distinction between prokaryotes and eukaryotes (meaning true kernel, also spelled "eucaryotes") is that eukaryotes have "true" nuclei containing their DNA, whereas the genetic material in prokaryotes is not membrane-bound. Eukaryotic organisms, such as humans, may be unicellular or multicellular. The difference between the structure of prokaryotes and eukaryotes is so great that it is considered to be the most important distinction among groups of organisms. Most prokaryotes are bacteria, and the two terms are often treated as synonyms. In 1977, Carl Woese proposed dividing prokaryotes into the Bacteria and Archaea (originally Eubacteria and Archaebacteria) because of the significant genetic differences between the two. This arrangement of Eukaryota (also called "Eukarya"), Bacteria, and Archaea is called the three-domain system replacing the traditional two-empire system. The cell structure of prokaryotes differs greatly from eukaryotes in many ways. The defining characteristic is the absence of a nucleus or nuclear envelope. Prokaryotes also were previously considered to lack cytoskeletons and do lack membrane-bound cell compartments such as vacuoles, endoplasmic reticulum/endoplasmic reticula, Golgi apparatus, mitochondria, and chloroplasts. In eukaryotes, the latter two perform various metabolic processes and are believed to have been derived from endosymbiotic bacteria. In prokaryotes similar processes occur across the cell membrane; endosymbionts are extremely rare. Prokaryotes also have cell walls, while some eukaryotes, particularly animals, do not. Both eukaryotes and prokaryotes have structures called ribosomes, which produce protein. Prokaryotes are usually much smaller than eukaryotic cells. Taking into account membrane bound organelles, prokaryotes also differ from eukaryotes in that they contain only a single loop of DNA stored in an area named the nucleoid. The DNA of the eukaryote is found on chromosomes. Prokaryotic DNA also lacks the proteins found in eukaryotic DNA. Prokaryotes have a larger surface area to volume ratio. This gives the Prokaryotes a higher metabolic rate, a higher growth rate and thus a smaller generation time as compared to the Eukaryotes. -- Landon Schuttler * * * * * * * * *