Structure and Function of Prokaryotes

Prokaryotes are simple unicellular organisms in which the genetic material is not enclosed in a cell nucleus. They are considered to be the first forms of life on earth. The actual word comes from the Greek language, where pro = before and karyo = cell.

Structure of Prokaryocytes

 * Small cells (1-5 μm)
 * Hereditary material (DNA) is not enclosed within nuclear membrane
 * No histones (specific basic proteins) bound to their DNA
 * No membrane bound organelles (eg mitochondria, chloroplasts)
 * No distinct nucleus, no chromosomes, no centrioles, no microtubules
 * Prokaryotes are divided into 2 domains: Bacteria and Archaea

Archaea:
 * Very similar to bacteria (in size, shape, absence of membrane bound organelles)
 * Until 1990, they were considered an unusual group of bacteria and named archaebacteria
 * They were given their own domain since they have went through an independent evolution and have many differences in their biochemistry from other forms of life
 * Archaea reproduce asexually and divide by binary fission, fragmentation, or budding; in contrast to bacteria and eukaryotes, no species of archaea are known that form spores.
 * Initially, archaea were seen as extremophiles that lived in harsh environments, such as hot springs and salt lakes, but they have since been found in a broad range of habitats, such as soils, oceans, and marshlands
 * One example are the methanogenic archaea that inhabit the gut of humans and ruminants, where they are present in vast numbers and aid in the digestion of food.
 * Archaea have some importance in technology, with methanogens used to produce biogas and as part of sewage treatment, and enzymes from extremophile archaea that can resist high temperatures and organic solvents are exploited in biotechnology.