The single celled bacterium has a cell wall made of the compound peptidoglycan covering the cell membrane. The cell has ribosomes but no membrane bound organelles. The outermost covering is the cell wall. Prokaryotes have no nuclear membrane around genetic material and no membrane bound cell organelles except mesosomes. They have only the 70s ribosomes.
All prokaryotes have a rigid cell wall, which protects and gives shape to the cell. The cell wall is made up of a chemical, peptidoglycan, unique to bacteria, lipids, polysaccharides and some proteins.
Pili are short and thin thread like tubular structures projecting out from the cell wall in some bacteria.
Some bacteria move with the help of one or more flagella. Flagella are longer and thicker than pili. Their structure is different from flagella of eukaryotes.
Plasma membrane, present below the cell wall, encloses the cytoplasm and other cell contents. It is made up of lipids and proteins, as in eukaryotes.
One circular chromosome made of a double helical molecule of DNA is located in a region of the cytoplasm called nucleoid. Apart from the chromosome, several species of bacteria possess one or more additional rings of DNA called plasmids, which replicate along with bacterial chromosome and bear genes for antibiotic resistance and act as the sex factor or F-factor.
Membrane bound organelles like endoplasmic reticulum, mitochondria, chloroplast, and golgi complex are absent. Only 70s ribosomes are present, which are different from those of eukaryotes.