Despite the great number of different shapes bacteria can have, the extracellular structures of different bacteria is very similar. All bacterial cell walls surrounding the prokaryotic organisms consits of peptidoglycans made from polysaccharide chains cross-linked by D-amino acid containing peptides. However, bacteria can be classified in one of two types, Gram-positive or Gram-negative bacteria which differ in their structural composition of the cell wall. While the cell wall of Gram-psoitive bacteria consists of many peptidoglycan layers and teichoic acid, the cell wall of Gram-negative bacteria only has a few layers of peptidoglycan but is surrounded by a lipid membrane of lipopolysaccharides and lipoproteins.
The cell membrane primarily consists of phospholipids building a natural barrier to keep nutrients, proteins and components of the cytoplasm. Different to eukaryotic cells, prokaryotic cells like bacteria do not contain specific cell compartments like nucleus, mitochondria or other organelles. Nevertheless some bacteria are able to separate single steps of the bacterial metabolims by protein-bound organelles, e.g. carboxysomes.