All bacteria are classified as prokaryotes, and common examples include E. coli and Streptococcus. Archaea, which has similarities to bacteria, is another domain that exclusively features prokaryotes. Prokaryotes are single-celled organisms that lack a nucleus and membrane-bound organelles such as mitochondria, chloroplasts, a golgi apparatus or an endoplasmic reticulum.
Although prokaryotic organisms lack the organelles of eukaryotes, they can have membrane systems within their semi-rigid cell walls. The prokaryote's cell walls are surrounded by either a gelatinous sheath or a capsule that better allows the organism to attach to different surfaces.
Fimbriae are hairlike structures that also assist in environmental attachment. The primitive organelles of the prokaryote are found together within the same body. These include various proteins, DNA and metabolites. The only shared organelle between a eukaryote and a prokaryote is the ribosome, although it is much smaller in the case of the prokaryote.
Prokaryotes reproduce asexually through binary fission, and they do not involve cellular mitosis. Genetic exchange can occur, but this is due to horizontal gene transfer. Prokaryotes, despite their unicellular nature, can form communities. These communities are encased in, and kept together by, a stabilizing polymer matrix, which is similar to slime. Most prokaryotic colonies start with more than one individual organism.