On the outside they have a strong cell wall. Beneath this is a membrane which will allow oily molecules to pass but prevents electrically charged molecules, and free protons and electrons, from passing through. Beneath this is a watery space full of molecules and ribosomes, messenger nucleic acids and all the other things needed to keep life going, all mixed up in a mostly chaotic way. There are some organelles within the cell, which function as storage compartments, but these do not have a membrane surrounding them as they do in eukaryotes. Instead they are surrounded by a protein coat.

At the center of the prokaryote is the nuclear region, but not separated from the rest of the cell by a membrane. This contains the DNA of the prokaryote, which is a long strand with its ends fixed together. The prokaryote may also contain shorter sequences of DNA called plasmids. These can move from one cell to another and carry information how to make proteins which inactivate antibiotics, for example.

At one end of the prokaryote there may be a wonderful little motor with a long stiff strand attached to it on the outside of the cell. As the motor rotates this strand is twirled around and pushes the cell along. So some prokaryotes can swim! The rod is called a flagellum or 'whip'.

In times of hardship, prokaryotes can shut down most of their life processes and wrap themselves up in a very hard outer coating.

To understand the size of prokaryotes, why not visit Soccearth?