Structure of a prokaryotic cell

Ultra structure of a prokaryotic cell:

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Figure: Ultra structure of a prokaryotic Cell Bacteria


The bacterium is bounded by two definite membranes estranged by the periplasmic space.  The outer layer is firm, serves for mechanical protection and is designated as cell wall. The chemical composition of the cell wall is instead complex; it has peptidoglycan, polysaccharides, protein and lipid molecules.

One of the most plentiful polypeptides, porin, forms channels which permit for the diffusion of solutes. Plasma membrane is a lipoprotein structure serving as a molecular blockade with surrounding medium. The plasma membrane controls the exit and entry of small molecules and ions. The enzymes included in the oxidation of metabolites (that is, the respiratory chain) and also the photosystems employed in photosynthesis, are existed in the plasma membrane of prokaryotes.

Bacterial chromosome is a single circular molecule of nude DNA tightly coiled in the nucleoid that appears in the electron microscope as a lighter area of the protoplasm. It is incredible to note that the DNA of E.coli that measures around 1mm long whenever uncoiled, has all the genetic information of organism. In this situation, there is adequate information to code for 2000 to 3000 distinct proteins.

The single chromosome or DNA molecule is circular and at one point it is joined to the plasma membrane and it is believed that this attachment might aid in the separation of two chromosomes after DNA replication.

Additionally to a chromosome, certain bacteria include a small, extra-chromosomal circular DNA termed as plasmid. The plasmid is responsible for antibiotic resistance in several bacteria. Such plasmids are very much employed in genetic engineering where the plasmids are estranged and reincorporated; genes (i.e., specific pieces of DNA) can be inserted into plasmids that are then transplanted into bacteria employing the methods of genetic engineering.

Surrounding the DNA in the darker area of the protoplasm are 20,000 to 30,000 particles termed as ribosomes. These are comprised of RNA and proteins and are the sites of protein synthesis. Ribosomes present in groups are termed as polysomes or polyribosomes. Each ribosome includes of a large and a small sub unit. The residue of the cell is filled with H2O, different RNAs, protein molecules (comprising enzymes) and different smaller molecules.

Some motile bacteria contain numerous, thin hair like processes of variable length termed as flagella. Flagella are employed for locomotion. In contrast with flagella of eukaryotic cells that contain 9+2 micortubles each flagellum in bacteria is made up of a single fibril.


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