Prokaryote
Say it: proh-KAR-ee-oht
A prokaryote is a usually single-celled organism, a bacterium or an archaeon, whose cell has no nucleus or other membrane-bound organelles.
Also: prokaryotes, procaryote, prokaryotic cell
Definition
What is a prokaryote?
A prokaryote is an organism whose cell lacks a nucleus. Its DNA, usually a single circular chromosome, lies in a region of the cytoplasm called the nucleoid, with no membrane around it. Prokaryotes make up two of the three domains of life, Bacteria and Archaea, and almost all of them live as single cells.
Like every cell, a prokaryote has a plasma membrane, cytoplasm, DNA and ribosomes, but its ribosomes (70S) are smaller than those in the eukaryotic cytoplasm (80S). Most have a cell wall outside the membrane; in bacteria the wall is built from peptidoglycan, a polymer that archaea lack. Many also carry plasmids, small extra circles of DNA that can hold genes such as those for antibiotic resistance, along with flagella for swimming and hair-like pili or fimbriae for sticking to surfaces or passing DNA to other cells.
Prokaryotic cells are typically much smaller than eukaryotic cells, often only one to a few micrometers across. That small size gives them a large surface area for their volume, so nutrients and wastes can spread through the cell by diffusion alone.
Word parts
Where does the word “prokaryote” come from?
- pro-
- beforeGreek pro
- kary-
- nut, kernel (here, the nucleus)Greek karyon
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Related
Terms that go with it
- EukaryoteA eukaryote is an organism whose cells keep their DNA inside a membrane-bound nucleus and contain other membrane-bound organelles.
- BacteriumA bacterium is a single-celled prokaryote with no nucleus, found in almost every habitat on Earth, including in and on the human body.
- ArchaeaArchaea are single-celled prokaryotes that form their own domain of life, distinct from bacteria in their membranes, cell walls and genes.
- PlasmidA plasmid is a small, usually circular DNA molecule that copies itself independently of the main chromosome, found mostly in bacteria.
- Binary fissionBinary fission is how bacteria and archaea reproduce: a cell copies its DNA, grows, and splits in the middle into two identical daughter cells.
- CellA cell is the smallest unit that can carry out all the processes of life, enclosed by a membrane and holding its own genetic material.
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Checked against
Written for biofideX in plain words, after checking these references:
- OpenStax Biology 2e, 4.2 Prokaryotic Cells
- OpenStax Microbiology, 3.3 Unique Characteristics of Prokaryotic Cells
- MeSH (NLM): Prokaryotic Cells
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