prokaryotes

(noun)

( /proʊkæri.oʊts/, pro-kah-ree-otes or /proʊkæriəts/, pro-kah-ree-əts) a group of organisms whose cells lack a cell nucleus (karyon), or any other membrane-bound organelles. Most prokaryotes are unicellular organisms, although a few such as myxobacteria have multicellular stages in their life cycles.

Related Terms

Examples of prokaryotes in the following topics:

  • Prokaryotic Reproduction

    • Reproduction in prokaryotes is asexual and usually takes place by binary fission.
    • The DNA of a prokaryote exists as as a single, circular chromosome.
    • In transformation, the prokaryote takes in DNA found in its environment that is shed by other prokaryotes.
    • Besides binary fission, there are three other mechanisms by which prokaryotes can exchange DNA.
    • In (a) transformation, the cell takes up prokaryotic DNA directly from the environment.

  • Prokaryotic versus Eukaryotic Gene Expression

    • Prokaryotes regulate gene expression by controlling the amount of transcription, whereas eukaryotic control is much more complex.
    • The process occurs in both prokaryotic and eukaryotic cells, just in slightly different manners.
    • Prokaryotic organisms are single-celled organisms that lack a defined nucleus; therefore, their DNA floats freely within the cell cytoplasm.
    • Therefore, in prokaryotic cells, the control of gene expression is mostly at the transcriptional level.
    • Prokaryotic transcription and translation occur simultaneously in the cytoplasm, and regulation occurs at the transcriptional level.

  • Classification of Prokaryotes

    • Prokaryotic organisms were the first living things on earth and still inhabit every environment, no matter how extreme.
    • Two of the three domains, Bacteria and Archaea, are prokaryotic.
    • Certain prokaryotes can live in extreme environments such as the Morning Glory pool, a hot spring in Yellowstone National Park.
    • The spring's vivid blue color is from the prokaryotes that thrive in its very hot waters.
    • Discuss the origins of prokaryotic organisms in terms of the geologic timeline

  • Characteristics of Eukaryotic DNA

    • Eukaryotes, having probably evolved from prokaryotes, have more complex traits in both cell and DNA organization.
    • It is probable that eukaryotic cells evolved from prokaryotic cells.
    • Prokaryotic DNA is found in circular, non-chromosomal form.
    • In addition, prokaryotes have plasmids, which are smaller pieces of circular DNA that can replicate separately from prokaryotic genomic DNA.
    • Eukaryotic DNA is stored in a nucleus, whereas prokaryotic DNA is in the cytoplasm in the form of a nucleoid.

  • Energy and Nutrient Requirements for Prokaryotes

    • Prokaryotes need a source of energy, a source of carbon, macronutrients, and micronutrients to survive.
    • When prokaryotes grow in nature, they obtain their nutrients from the environment.
    • Autotrophic prokaryotes synthesize organic molecules from carbon dioxide.
    • In contrast, heterotrophic prokaryotes obtain carbon from organic compounds.
    • Table 1 summarizes carbon and energy sources in prokaryotes .

  • The Role of Prokaryotes in Ecosystems

    • Prokaryotes are ubiquitous: There is no niche or ecosystem in which they are not present.
    • Prokaryotes play an important role in the carbon cycle .
    • In anoxic sediments, prokaryotes, mostly archaea, produce methane (CH4).
    • Prokaryotes play a significant role in continuously moving carbon through the biosphere.
    • Give examples of the beneficial roles played by prokaryotes in different ecosystems

  • Characteristics of Prokaryotic Cells

    • Prokaryotic DNA is found in a central part of the cell: the nucleoid .
    • Most prokaryotes have a peptidoglycan cell wall and many have a polysaccharide capsule .
    • Some prokaryotes have flagella, pili, or fimbriae.
    • Similarly, any wastes produced within a prokaryotic cell can quickly diffuse out.
    • Small size, in general, is necessary for all cells, whether prokaryotic or eukaryotic.

  • Bacterial Chromosomes in the Nucleoid

    • A genophore is the DNA of a prokaryote.
    • It is commonly referred to as a prokaryotic chromosome.
    • The genophore is circular in most prokaryotes, and linear in very few.
    • These organelles are very similar to true prokaryotes.
    • Prokaryote cell (right) showing the nucleoid in comparison to a eukaryotic cell (left) showing the nucleus.

  • Binary Fission

    • Binary fission is the method by which prokaryotes produce new individuals that are genetically identical to the parent organism.
    • Prokaryotes, such as bacteria, propagate by binary fission.
    • In both prokaryotic and eukaryotic cells, the outcome of cell reproduction is a pair of daughter cells that are genetically identical to the parent cell.
    • Prokaryotic cells, on the other hand, do not undergo karyokinesis and, therefore, have no need for a mitotic spindle.
    • While both proteins are found in extant organisms, tubulin function has evolved and diversified tremendously since evolving from its FtsZ prokaryotic origin.

  • Elongation and Termination in Prokaryotes

    • Once a gene is transcribed, the prokaryotic polymerase needs to be instructed to dissociate from the DNA template and liberate the newly-made mRNA.
    • By the time termination occurs, the prokaryotic transcript would already have been used to begin synthesis of numerous copies of the encoded protein because these processes can occur concurrently in the cytoplasm.
    • The unification of transcription, translation, and even mRNA degradation is possible because all of these processes occur in the same 5' to 3' direction and because there is no membranous compartmentalization in the prokaryotic cell.
    • During elongation, the prokaryotic RNA polymerase tracks along the DNA template, synthesizes mRNA in the 5' to 3' direction, and unwinds and rewinds the DNA as it is read.