DNA is present as a single circular molecule called a BACTERIAL CHROMOSOME
DNA is naked having no associated histone proteins
No membrane bound organelles
Apart from the DNA nucleoid, there is little internal structure apart from dissolved substances and a large number of RIBOSOMES essential for PROTEIN SYNTHESIS
The cytosol is an effective site for bacterial cell metabolism. This allows bacteria to adapt quickly to changing nutritional conditions, but means the regulation of genetic and metabolic activity has to be tightly regulated.
Divide by BINARY FISSION
Some prokaryotic cells have external whip-like FLAGELLA for locomotion or hair like PILI for adhesion.
Prokaryotic cells come in multiple shapes: cocci (round), baccilli (rods), and spirilla or spirochetes (helical cells).
A pilus ( Latin ; plural : pili ) is a hairlike protein structure on the surface of a bacterial cell, required for bacterial conjugation (transfer of genetic material)
A fimbrium (Latin; plural: fimbria ) is a short pilus that is used to attach the cell to a surface. Mutant bacteria that lack fimbria cannot adhere to their usual target surfaces and, thus, cannot cause diseases.
These are produced by some bacteria to survive unfavourable environmental conditions. Dormant forms are metabolically inactive and only germinate under suitable conditions
ENDOSPORES : a dormant , tough, non-reproductive structure produced by a small number of bacteria . The primary function of most endospores is to ensure the survival of a bacterium through periods of environmental stress. They are therefore resistant to ultraviolet and gamma radiation , desiccation , lysozyme , temperature , starvation , and chemical disinfectants . Endospores are commonly found in soil and water, where they may survive for long periods of time e.g. Clostridium (tetanus, gas gangrene), Bacillus (anthrax) CYSTS : also dormant, but unlike endospores are not resistant to heating at high temperatures
Cell size ranges from 10 – 150um Cell size ranges from 0.5um to 100um No mucilaginous capsule present (numerous internal structures present including microtubules, ER, Golgi, secretory vesicles etc) Mucilaginous capsule Have cilia or flagella (for movement) Have pili & fimbriae (for adhesion) and flagella (for propulsion) Membrane bound organelles (compartmentalisation) No membrane bound organelles Cell walls, if present, made of cellulose (chitin in fungi) Cell walls made of peptidoglycan (Thickness of wall depends on whether the cell is Gram +ve or –ve) Membrane bound nucleus No membrane bound nucleus EUKARYOTES PROKARYOTES
Comparison of Prokaryotic and Eukaryotic Cells