There are two kinds of cellular organisms known as prokaryotes and eukaryotes.
The term prokaryotes means before the nucleus: (pro - before, karyon -nucleus). Prokaryote includes bacteria and cyanobacteria or blue green algae. Prokaryotic cells have no membrane bound nucleus, nor do any other well-developed membrane bound compartments in the cytoplasm, for that matter, these cells have only plasma membrane, cytoplasm and a nucleoid. The nucleoid is an irregularly shaped region in which DNA is concentrated. They have circular DNA. They all have ribosomes.
|Bacterium, a Prokaryotic cell|
The term eukaryote means, true nucleus (Eu - true, Karyon nucleus). It includes protists, fungi, plants and animals. Eukaryotes have evolved from prokaryotes. They have specialized membrane-bound compartments or organelle. The most conspicuous of these organelles is the nucleus. Its DNA is linear.
Despite the many significant differences between prokaryotic and eukaryotic cells, there are striking functional similarities at the biochemical level. The genetic code in DNA of both is the same; many basic metabolic processes are same in both types of cells.