As opposed to eukaryotic cells, which contain their genetic material inside a nucleus, prokaryotic cells allow their genetic material to float in the cell’s cytoplasm. In fact, prokaryotic cells lack any internal, membrane-bound organelles. While both types of cells use DNA as their primary genetic material, prokaryotes arrange their DNA in a simple circle, as opposed to bundling it into several chromosomes, as eukaryotes do.
Despite the lack of a nucleus, prokaryotic cells concentrate their circular ring of DNA in a small portion of the cell called a nucleoid, but a membrane does not bind this DNA together. In general, prokaryotic cells are small relative to eukaryotic cells. This difference occurs in part because of the constraints prokaryotes experience in trying to transport resources around the cell with no organelles.
Prokaryotes pre-date eukaryotes significantly, and their primitive structure illustrates this. Part of their success lies in their ability to exchange genetic material directly with other cells. Called horizontal gene transfer, this ability allows for the antibiotic resistance. Prokaryotes use small rings of DNA, called plasmids, as the method for horizontal gene transfer.
Most prokaryotic cells feature a flagellum, which is a long, whip-like tail that propels them through their environment. Eukaryotic cells feature different types of locomotor structures, depending on their function.