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Prokaryotes are a group of organisms which are separate from eukaryotes. Unlike eukaryotes, they do not have membrane-bound organelles such as the nuclei and mitochondria. Prokaryotes have a Cell wall made out of peptidoglycan which provides support for the cell and protects it against damage from osmotic rupture or mechanical stress. Their genetic material floats free in the cytoplasm of the cells, in contrast to the nuclei enclosed DNA of eukaryotes. They also have 70s ribosomes and a plasma membrane. An example of a prokaryote is E. coli. Prokaryotes can be classified into two domains:

  1. Bacteria
  2. Archaea

Some of them live in adverse environments, such as hot springs and salt lakes, which are considered to be inhospitable to sustain the life of other kinds of organisms. Arachea, also known as extremophiles, have structures that are non-typical to other kinds of eukaryotes and bacteria. Unlike normal plasma membrane which is made of a phospholipid bilayer, some of their plasma membranes are composed of phospholipid monolayer; these archaea fuse the heads of the phospholipid molecules into a single molecule with two hydrophilic heads. This might help the organism to be more rigid and to adapt better to the harsh environment. Ferroplasma is one of the members of the archaean which lives in extremely acidic habitat, having this extraordinary structure is thought to aid their survival.

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