Ultrastructure of a Bacterial cell

A bacterial cell, from the outside in, reveals three broad layers: (i) the capsule/glycocalyx, (ii) the cell wall, and (iii) the cytoplasm, the last of which houses several distinct internal structures. The cytoplasm is thick and semi-transparent, and holds ribosomes plus inclusions such as glycogen, poly-beta-hydroxybutyrate granules, sulphur granules and gas vesicles. The bacterial chromosome is a single, tightly-coiled, circular DNA molecule - not enclosed in a membrane the way a eukaryotic chromosome is, and not associated with histone proteins - called the nucleoid or genophore; remarkably, the DNA of E. coli, though only about 1 mm long when fully uncoiled, carries the organism's entire genetic information, and it stays attached to the plasma membrane at one point, which is thought to help separate the two daughter chromosomes after replication. A plasmid is a separate, small, double-stranded, circular, self-replicating piece of DNA (1-500 kb, usually 0.5-5.0% of the cell's total DNA) that is not part of the main chromosome; plasmids carry genes for fertility, antibiotic resistance and heavy-metal handling, and can also direct the production of bacteriocins and toxins, coming in several named functional types - F (fertility), R (resistance), Col (colicin), Ri (root-inducing) and Ti (tumour-inducing) plasmids. The capsule/glycocalyx is a gelatinous, polysaccharide-and/or-polypeptide layer around some bacteria; when it is thick and tightly bound to the cell wall it is called a capsule, and it protects the cell from desiccation and antibiotics while its sticky texture helps the cell attach to surfaces such as plant roots or human teeth. The cell wall is rigid and granular, giving the cell its shape and physical protection, built chemically from peptidoglycan/mucopeptide (N-acetyl glucosamine + N-acetyl muramic acid + a short peptide chain); a highly abundant wall protein called porin helps solutes diffuse across it. The plasma membrane, made of lipoprotein, controls what enters and leaves the cell, and also houses both the respiratory-chain enzymes and (in photosynthetic bacteria) the photosystems. Beyond these three layers, mesosomes are infoldings of the plasma membrane (vesicles, tubules, lamellae) that increase membrane surface area and assist respiration and binary fission; polyribosomes/polysomes are clusters of 70S ribosomes (mad …