Scientist Dougherty first classified the cells in 1957. Cells are classified on the basis of structural organisation of their nucleus into two main types that are prokaryotic cells and eukaryotic cell. The term “pro” means premitive and “karyoplasms” means nucleus.
Examples of prokaryotic cells are - different types of bacteria (cocci, bacillus, spirilum) etc.
Definition of prokaryotic cell - Prokaryotic cells are the organisms that do not have membrane bound organelles and well defined nucleus, nucleoid is present instead of nucleus.
Definition of eukaryotic cell - Eukaryotic cells are the organism in which membrane bound organelles, well defined nucleus is present in it. Their genetic material is well placed and proper DNA is present.
Prokaryotic cells - prokaryotic cells are premitive plant cells that having the simplest organisation. Prokaryotic cells include bacteria, blue green algae, mycoplasma or PPLO that is pkeuro pneumonia like organisms, rickettsiae and spirochaete. Prokaryotic cells are smaller than eukaryotic cells in size. Cells of prokaryotes contain mass of protoplasm and is covered by cell covering. Each cell is bounded by a complex cell wall beneath which the plasma membrane lies. Plasma membrane surrounds the protoplasm of the cell. In some places plasma membrane invaginated to form internal membranous structure. Protoplasm of prokaryotic cells are not well defined like eukaryotic cell. Means protoplasm is not divided into nucleus and cytoplasm. In eukaryotic cells nucleus contains genetic material which is membrane bound but in prokaryotic cells genetic material is localised in a discrete region called nucleoid or genophore or chromatin body. It is made up of DNA threads. Here DNA is not complexed with his tone proteins and it does not form chromosome. That means true chromosome are not formed. The nucleoid is not separated by the delimiting membrane. Thus the genetic material of the prokaryotic cells called nucleoid. Here in prokaryotic cell DNA threads are divided by binary fission.
of prokaryotic cell - Prokaryotic cells do not have any membrane bound
organelles like mitochondria, plastids, endoplasmic reticulum, Golgi body etc.
In the prokaryotic cell plasma membranes are folded in different regions to
form mesosome or are called desmosome which may contain respiratory enzymes and
it may function as mitochondria.
Pigments - Photosynthetic pigments are present in vesicles like chromatophores, disc like thylakoids, tubules like lamellae. These together are considering as plastids. As true plastids are not present in the prokaryotic cells.
Ribosome in prokaryotic cells - Ribosome are 70S in prokaryotic cells. The bigger subunit is 50s and the smaller subunit is 30s. Ribosomes and inclusion bodies are freely scattered on the cytoplasm. Ribosomes are not associated with a membranous organelles as they are not present.
Cell wall – Prokaryotic cell wall is made up of nitrogen containing complex of compound that is made up of mucopeptide in nature.
Microtubules - Microtubules are not present in the prokaryotic cells.
Flagellum of prokaryotic cell - flagella is simple and 9+2 organisation is absent. It is a whip like structure associated with locomotion of prokaryotes.
Pilli of prokaryotic cell - Different types of Pilli are present in prokaryotic cell .
In some cases glycoprotein’s are present.