ABSTRACT
https://www.niso.org/standards/z39-96/ns/oasis-exchange/table"> The prokaryotic cell The model Bacterial cell is that of Escherichia coli, a rod-shaped cell about 2 μm long and 1 μm wide. With a very few exceptions, there are no discernible subcellular components in prokaryotic cells. At the biochemical and physiological level, Bacteria have some similarity to the Archaea, yet the Archaea have similarities to both the Bacteria and the Eukaryotes. The cytoplasmic membrane The Bacterial cell membrane is made up of a lipid bilayer with proteins buried within it. The bilayer is impermeable to most molecules except gases such as oxygen, nitrogen, and CO2, while passage of larger molecules and ions is mediated by protein. The membrane does not confer rigidity to the cell but is reinforced with hopanoids. The Archaeal cell membrane has a similar arrangement but has a unique monolayer structure. The cytoplasm Subcellular structures in the aqueous cytoplasm include ribosomes and storage structures (inclusion bodies, carboxysomes, and magnetosomes). Activity-specific structures also exist, for example, thylakoid membranes or chlorosomes involved in photosynthesis. The examination of subcellular structure in prokaryotes is sometimes complicated by the process of electron microscopy and this has been implicated in the formation of artifacts such as the mesosome. Genomic material The nucleoid is the tightly packed chromosomal material of prokaryotes, while plasmids are thought to float free in the cytoplasm. The chromosomal complement of a prokaryotic cell is always haploid and plasmid copy number is often more than one. The periplasm The periplasm of Gram-negative Bacteria is of lower water content than the cytoplasm. It is packed with proteins and plays a major role in secretion, environmental sensing, and many other key pathways. The cell wall All prokaryotic cells have a strong cell wall (apart from Mycoplasma and Thermoplasma). Bacteria are covered in peptidoglycan. The Archaea have a far greater variety in the composition of the outer wall but have a Bacterial ortholog in pseudomurein. Endospores Clostridium and Bacillus are able to form spores within the cytoplasm in response to cell starvation. Endospores have the capacity to survive heat, radiation, and chemical disinfectants. External features All prokaryotes are covered in some form of slime capsule (or glycocalyx). In addition they may have filaments extending from the cell wall such as flagella for movement, or much finer fimbriae for attachment. Related topics (C2) Prokaryotic diversity (C9) Cell division (C6) The major prokaryotic groups (C10) Bacterial flagella and movement (C8) The bacterial cell wall (F2) Genomes 46
