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The chemical structure of the outer membrane's lipopolysaccharide is often unique to specific bacterial sub-species and is responsible for many of the antigenic properties of these strains. In addition to the peptidoglycan layer the Gram-negative cell wall also contains an additional outer membrane composed of phospholipids and ...
The outer membranes of a bacterium can contain a huge number of proteins. In E. Coli for example there are around 500,000 in the membrane. [5] Bacterial outer membrane proteins typically have a unique beta barrel structure that spans the membrane. The beta barrels fold to expose a hydrophobic surface before their insertion into the outer membrane.
For many bacteria, the S-layer represents the outermost interaction zone with their respective environment. [ 9 ] [ 2 ] Its functions are very diverse and vary from species to species. In many archaeal species the S-layer is the only cell wall component and, therefore, is important for mechanical and osmotic stabilization.
In its place is a short oligosaccharide: this form is known as Lipooligosaccharide (LOS), and is a glycolipid found in the outer membrane of some types of Gram-negative bacteria, such as Neisseria spp. and Haemophilus spp. [7] [22] LOS plays a central role in maintaining the integrity and functionality of the outer membrane of the Gram negative ...
The Mycobacteria (acid-fast bacteria) have a cell envelope which is not typical of Gram-positives or Gram-negatives. The mycobacterial cell envelope does not consist of the outer membrane characteristic of Gram-negatives, but has a significant peptidoglycan-arabinogalactan-mycolic acid wall structure which provides an external permeability barrier.
All of the organs that rise from the ectoderm such as the nervous system, teeth, hair and many exocrine glands, originate from two adjacent tissue layers: the epithelium and the mesenchyme. [8] Several signals mediate the organogenesis of the ectoderm such as: FGF , TGFβ , Wnt , and regulators from the hedgehog family .
[7] [12] The diderm bacteria can also be further differentiated between simple diderms lacking lipopolysaccharide (LPS); the archetypical diderm bacteria, in which the outer cell membrane contains lipopolysaccharide; and the diderm bacteria in which the outer cell membrane is made up of mycolic acid (e. g. Mycobacterium). [9] [10] [12] [13]
Some bacteria have cell wall structures that are neither classically Gram-positive or Gram-negative. This includes clinically important bacteria such as mycobacteria which have a thick peptidoglycan cell wall like a Gram-positive bacterium, but also a second outer layer of lipids. [78]