All living things are made up of a cell or cells, and all cells are either prokaryotic or eukaryotic. A eukaryotic cell is a complex cell with a nucleus and many organelles. Eukaryotic cells are the building blocks of all animals, plants and fungi. Prokaryotic cells are very simple cells with fewer structures than eukaryotic cells; one primary difference is that they lack a nucleus. Bacteria are an example of prokaryotes.
Prokaryotic cells do not contain the extensive network of organelles found in eukaryotic cells. The nucleus, mitochondria, chloroplasts, Golgi apparatus and endoplasmic reticulum are all absent in prokaryotic cells. Instead, the enzymes in organelles of eukaryotic cells are attached to the plasma membrane that surrounds the cell.
The only true organelles in a prokaryotic cell are ribosomes, which are cytoplasmic organelles. Ribonucleic acid (RNA) in the ribosomes receives information from the cell’s deoxyribonucleic acid (DNA) to create protein.
Although the prokaryotic cell does not have a defined, membrane-bound nucleus like the eukaryotic cell, it does have a region called the nucleoid. The nucleoid is an area at the center of the cell where DNA is located. In eukaryotic cells, DNA is linear, but in prokaryotic cells, DNA is circular and may be 500 times the length of the cell.
Because of the simple structure of the prokaryotic cell, it reproduces by binary fission rather than mitosis. The DNA replicates itself and the DNA molecules attach themselves to the cell membrane. As the cell widens, the DNA strands separate. When the cell is about double in size, the plasma membrane grows inward, creating two separate cells.