The cell wall

Prokaryotic cells are strong compared with eukaryotic single cells.  The basis of their strength comes from the cell wall that is present in all prokaryotes apart from the Archaeal Thermoplasma and Bacterium Mycoplasma. The Bacteria are covered in a semi- rigid compound called peptidoglycan in most cases with the exception of the Chlamydia. In these Bacteria the cell wall rigidity is provided through cysteine-rich membrane proteins interlinked with disulfide bonds. The Archaea have a far greater variety in the composition of the outer wall but have a Bacterial ortholog in pseudomurein.