The prokaryotes are generally divided into two main groups like
the archaebacteria and bacteria (the latter is also known as
eubacteria).
Compared to bacteria, archaebacteria present basic differences,
such as the chemical composition of their plasma membrane and cell
wall and different enzymes related to DNA and RNA metabolism.
In general, prokaryotic cells are those that do not have a
membrane-bound nucleus. In fact "pro-karyotic" is
Greek for "before nucleus".
Besides bacteria, the cyanobacteria (blue-green algae) are a
major group of prokaryotes.