Pierce, Marcia M. Department of Biological Sciences, Eastern Kentucky University, Richmond, Kentucky.
Last reviewed:January 2018
Show previous versions
- Bacteria and Archaea
- Links to Primary Literature
- Additional Readings
Any of the unicellular microorganisms belonging to the Bacteria and Archaea domains that lack a true nucleus or any other membrane-bound organelle. Taxonomists divide prokaryotic organisms into two domains: Bacteria and Archaea. In the past, all prokaryotes were collected into a single taxonomic grouping termed the Prokaryotae, but this term is no longer in use. Prokaryotic cells (see illustration) are usually microscopic, but some are visible to the naked eye. Instead of a nucleus, prokaryotic cells contain a nucleoid, which is a deoxyribonucleic acid (DNA)–dense region of the cell in which DNA replication and transcription occur. The chromosome of these cells is circular and, in contrast to eukaryotic cells, continuously codes for cellular proteins and other molecules. Some cells also contain a plasmid, which is a smaller separate piece of circular DNA. The ribosomes of prokaryotes are found floating loose in the cytoplasm (in eukaryotic cells, the ribosomes are found in or on the rough endoplasmic reticulum), and these cell organelles convert stored genetic information into protein molecules. Most prokaryotes are found as single-cell microorganisms; however, some species form filamentous, mycelial, or colonial structures. See also: Archaea; Bacteria; Biological classification; Cell organization; Chromosome; Deoxyribonucleic acid (DNA); Eukaryota; Plasmid; Ribosomes
The content above is only an excerpt.
for your institution. Subscribe
To learn more about subscribing to AccessScience, or to request a no-risk trial of this award-winning scientific reference for your institution, fill in your information and a member of our Sales Team will contact you as soon as possible.
to your librarian. Recommend
Let your librarian know about the award-winning gateway to the most trustworthy and accurate scientific information.
AccessScience provides the most accurate and trustworthy scientific information available.
Recognized as an award-winning gateway to scientific knowledge, AccessScience is an amazing online resource that contains high-quality reference material written specifically for students. Contributors include more than 9000 highly qualified scientists and 43 Nobel Prize winners.
MORE THAN 8700 articles covering all major scientific disciplines and encompassing the McGraw-Hill Encyclopedia of Science & Technology and McGraw-Hill Yearbook of Science & Technology
115,000-PLUS definitions from the McGraw-Hill Dictionary of Scientific and Technical Terms
3000 biographies of notable scientific figures
MORE THAN 19,000 downloadable images and animations illustrating key topics
ENGAGING VIDEOS highlighting the life and work of award-winning scientists
SUGGESTIONS FOR FURTHER STUDY and additional readings to guide students to deeper understanding and research
LINKS TO CITABLE LITERATURE help students expand their knowledge using primary sources of information