Glossary
prokaryote
A prokaryote is a cell with no nucleus and no membrane-bound organelles — its DNA sits loose in the cytoplasm, as it does in bacteria.
A prokaryote is a cell with no nucleus and no membrane-bound organelles. Its DNA is a single circular chromosome lying free in the cytoplasm, often beside smaller rings called plasmids, and its only organelles are ribosomes, which have no membrane of their own. Everything else a eukaryotic cell does in a compartment — the chemical work of the cell — happens in the one open space. Bacteria and the archaea are prokaryotes, and they are small: a bacterium is roughly a thousandth the volume of a human cell, which is why it can feed and get rid of waste by diffusion alone. They divide by binary fission, an exact copy of the chromosome and a split in two, without the spindle and paired chromosomes of mitosis. Two points get tested: a prokaryote has ribosomes but no mitochondria, and its lack of a nucleus is the definition.
Taught in
Related terms
- eukaryote — A eukaryote is a cell with a true nucleus and membrane-bound organelles — the cells of plants, animals, fungi and protists.
- cell theory — The cell theory is the claim that every living thing is made of cells, that the cell is the basic unit of structure and function, and that cells come from existing cells.
- nucleotide — A nucleotide is the building block of DNA and RNA: a phosphate, a five-carbon sugar, and one of the nitrogenous bases.
- virus — A virus is genetic material wrapped in a protein coat — it has no cell, no metabolism, and can only reproduce inside a host cell.
- Gram stain — A Gram stain is a four-reagent differential stain that sorts bacteria by cell wall: a thick wall holds the purple dye (Gram-positive), a thin wall loses it and takes the pink counterstain (Gram-negative).
Source: The biology guide in this course: its genetics definitions follow the National Human Genome Research Institute's Talking Glossary of Genomic and Genetic Terms, and its process descriptions follow the US National Cancer Institute's SEER Training Modules. Both are US federal government material, not subject to copyright in the United States. The microbiology entries — the bacterial cell, the Gram stain and the chain of infection — were written for this course from the infection-control guidance the biology guide's own source list names (US Centers for Disease Control and Prevention), which the genetics glossary does not cover. The definitions above are written for this course in our own words. (NHGRI Talking Glossary accessed 2026-10-26; definitions written 2026-10-27; the CDC basis for the microbiology entries — Principles of Epidemiology in Public Health Practice, third edition — accessed 2026-10-28, the date the biology guide's own source list records)