Prokaryotic cells are the simplest systems that exhibit all of the signs of life. Despite their small size, inside each cell there is the forex order flow information eukaryotic cells chemical and biochemical machinery necessary for growth, reproduction and the acquisition and utilization of energy. Prokaryotes have a large array of abilities. Energy comes in many forms, and various types of prokaryotic cells are adept at using almost all of them.
In large measure the actual structure of one of these cells reflects the way in which it acquires energy, but, despite their diversity, all prokaryotic cells have the following features in common. Just inside the cell wall, the plasma membrane is a selective barrier which regulates the passage of materials to from the cell. It is through this membrane that a cell must exchange food molecules, gases and other vital ingredients. Composed of phospholipid and protein membranes form thin, flexible, self-sealing, highly selective barriers between the inside of the cell and the outside world.
Within the plasma membrane is a viscous solution of proteins and other soluble materials. This is the cytoplasm, a complex semifluid material that holds all the molecules, large and small, necessary for carrying out the major metabolic reactions. The cytoplasm is not subdivided by membranes into organelles, a lack of compartmentalization that is most evident when we look at the organization of the genetic material. Genetic information in prokaryotic cells is carried on a single circular piece of DNA which is attached to the cell membrane and in direct contact with the cytoplasm.
There is no enclosing membrane, so there is no true nucleus, but simply a concentration of DNA known as a nucleoid. There are no special proteins associated with this DNA molecule. Some prokaryotes also carry smaller circles of DNA called plasmids. The genetic information on the plasmids is transferrable between cells, allowing prokaryotes to share such abilities as antibiotic resistance.
Humans have discovered that prokaryotic plasmids can be genetically engineered. Today, they are isolated, changed to carry other interesting information and then reintroduced into new cells. Some prokaryotes propel themselves by means of whip-like filaments called flagella. These are strands of protein that pass though the outer surface of the cell body either either singly or in tufts. Energy provided by the plasma membrane rotates the flagellum by means of a unique rotating ‘joint’ and this in turn moves the bacterium through its liquid world. Prokaryotic cells also contain ribosomes, small complexes of RNA and protein, on which new proteins are assembled.