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Diagram of a prokaryotic cell, a bacterium with a flagellum. A prokaryote (/ p r oʊ ˈ k ær i oʊ t,-ə t /; less commonly spelled procaryote) [1] is a single-celled organism whose cell lacks a nucleus and other membrane-bound organelles. [2]
The DNA of a prokaryotic cell consists of a single circular chromosome that is in direct contact with the cytoplasm. The nuclear region in the cytoplasm is called the nucleoid. Most prokaryotes are the smallest of all organisms, ranging from 0.5 to 2.0 μm in diameter. [1] [page needed] A prokaryotic cell has three regions:
Typical prokaryotic cell structure. Prokaryotes have DNA located in an area called the nucleoid, which is not separated from other parts of the cell by a membrane. There are two domains of prokaryotes: bacteria and archaea. Prokaryotes have fewer organelles than eukaryotes.
A drawing of a prokaryotic cell. There are two fundamental classifications of cells: prokaryotic and eukaryotic. Prokaryotic cells are distinguished from eukaryotic cells by the absence of a cell nucleus or other membrane-bound organelle. [10] Prokaryotic cells are much smaller than eukaryotic cells, making them the smallest form of life. [11]
Some eukaryotic cells also use flagella—and they can be found in some protists and plants as well as animal cells. Eukaryotic flagella are complex cellular projections that lash back and forth, rather than in a circular motion. Prokaryotic flagella use a rotary motor, and the eukaryotic flagella use a complex sliding filament system.
Cell division in prokaryotes (binary fission) and eukaryotes (mitosis and meiosis).The thick lines are chromosomes, and the thin blue lines are fibers pulling on the chromosomes and pushing the ends of the cell apart.
The nucleoid (meaning nucleus-like) is an irregularly shaped region within the prokaryotic cell that contains all or most of the genetic material. [1] [2] [3] The chromosome of a typical prokaryote is circular, and its length is very large compared to the cell dimensions, so it needs to be compacted in order to fit.
Although probable prokaryotic cell fossils date to almost 3.5 billion years ago, most prokaryotes do not have distinctive morphologies, and fossil shapes cannot be used to identify them as archaea. [58] Instead, chemical fossils of unique lipids are more informative because such compounds do not occur in other organisms. [59]