Prokaryotes include the kingdoms of Monera (simple bacteria) and Archaea. At a basic level a prokaryote is an aqueous emulsion containing biomolecules and other substances surrounded by a membrane and a cell wall. Prokaryotic cells don't possess membrane bound organelles. Of course things are never that simple in biology. At least some prokaryotes do contain intracellular structures that can be seen as primitive organelles. Intracellular membranes are known in some groups of prokaryotes, such as membrane systems devoted to special metabolic properties.
For the future doctor, prokaryotes are an important subject of study given that many infectious diseases arise from bacterial infection. In addition to an awareness of the structural features of bacterial cells, you should have a good basic sense of morphological classification in bacteria, modes of reproduction and DNA transfer, and an understanding of sociality in bacteria and patterns of interacting with the environment.
The Prokaryotic Cell Images
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Conceptual Vocabulary for Prokaryotes
Prokaryotes are a group of organisms that lack a cell nucleus, or any other membrane-bound organelles.
In prokaryotes, the nucleoid (also known as the nuclear region, nuclear body or chromatin body) is an irregularly shaped region where the genetic material is localized.
A ribosome is a small, dense, functional structure found in most known cells that assembles proteins and polypeptides used in cell division.
A flagellum is a long, slender projection from the cell body, composed of microtubules and surrounded by the plasma membrane.
A cell wall is a fairly rigid layer surrounding a prokaryotic cell, located external to the cell membrane, which provides the cell with structural support, protection, and acts as a filtering mechanism.
Peptidoglycan, also known as murein, is a polymer consisting of sugars and amino acids that forms a mesh-like layer outside the plasma membrane of eubacteria.
A pilus is a hairlike appendage found on the surface of many bacteria. This term and fimbria are often used interchangeably.
Flagellin is a protein that arranges itself in a hollow cylinder to form the filament in bacterial flagellum
Gram-positive bacteria are those that retain a crystal violet dye during the Gram stain process.
A lipopolysaccharide is a large molecule consisting of a lipid and a polysaccharide (carbohydrate) joined by a covalent bond.
The cell envelope is the cell membrane and cell wall plus an outer membrane, if one is present. Most bacterial cell envelopes fall into two major categories: Gram positive and Gram negative.
The outer membrane refers to the outside membranes of Gram-negative bacteria.
The periplasmic space is the space seen between the plasma membrane and the outer membrane in the gram-negative bacteria.
Glycocalyx is a general term referring to extracellular polymeric material produced by some bacteria, epithelia and other cells.
The carboxysome is a bacterial microcompartment, roughly 90-500 nm in diameter, made up of a protein shell, that contains enzymes involved in carbon fixation reactions.
A fimbria is a proteinaceous appendage in many gram-negative bacteria that is thinner and shorter than a flagellum.
A genophore is the DNA of a prokaryote.
A S-layer (surface layer) is a part of the cell envelope commonly found in bacteria, as well as among archaea. It consists of a monomolecular layer composed of identical proteins or glycoproteins.
Endotoxins are potentially toxic, natural compounds found inside pathogens such as bacteria, released mainly when bacteria are lysed.
Teichoic acids are polymers of glycerol or ribitol linked via phosphodiester bonds. These acids can be found in the cell wall of gram-positive bacteria and appear to extend to the surface of the peptidoglycan layer.
Lipoteichoic acid is a surface-associated adhesion amphiphile from Gram-positive bacteria and regulator of autolytic wall enzymes (muramidases).
FtsZ is a protein that assembles into a ring at the future site of the septum of bacterial cell division. Named after filamenting temperature-sensitive mutant Z, is a prokaryotic homologue to the eukaryotic protein tubulin.
MreB is a protein found in bacteria that has been identified as a homologue of actin, as indicated by similarities in tertiary structure and conservation of active site peptide sequence.
A chlorosome is a photosynthetic antenna complex found in green sulfur bacteria and some green filamentous anoxygenic phototrophs.
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