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Archaea and bacteria have generally similar cell structure, but cell composition and organization set the archaea apart. Like bacteria, archaea lack interior membranes and organelles . [ 68 ] Like bacteria, the cell membranes of archaea are usually bounded by a cell wall and they swim using one or more flagella . [ 119 ]
By contrast, the exoplasmic side (the side on the exterior of the cell) consists mainly of phosphatidylcholine and sphingomyelin, a type of sphingolipid. Each glycerophospholipid molecule consists of a small polar head group and two long hydrophobic chains. In the cell membrane, the two layers of phospholipids are arranged as follows:
The cell membrane of archaea consist mostly of ether phospholipids. These lipids have a flipped chirality compared to bacterial and eukaryotic membranes, a conundrum known as the "lipid divide". The "tail" groups are also not simply n-alkyl groups, but highly methylated chains made up of saturated isoprenoid units (e.g. phytanyl). [15]
The cell envelope is composed of the cell membrane and the cell wall. As in other organisms, the bacterial cell wall provides structural integrity to the cell. In prokaryotes , the primary function of the cell wall is to protect the cell from internal turgor pressure caused by the much higher concentrations of proteins and other molecules ...
For example, while bacterial cell membranes are made from phosphoglycerides with ester bonds, Achaean membranes are made of ether lipids. [43] Archaea were originally described as extremophiles living in extreme environments, such as hot springs, but have since been found in all types of habitats. [44]
Like all archaea, Thermoproteus possesses unique membrane lipids, which are ether-linked glycerol derivatives of 20 or 40 carbon branched lipids. The lipids' unsaturations are generally conjugated (as opposed to the unconjugation found in Bacteria and Eukaryota).
These microbes are prokaryotes, meaning they have no cell nucleus or any other membrane-bound organelles in their cells. Archaea were initially classified as bacteria, but this classification is outdated. [93] Archaeal cells have unique properties separating them from the other two domains of life, Bacteria and Eukaryota.
The general lack of internal membranes in bacteria means these reactions, such as electron transport, occur across the cell membrane between the cytoplasm and the outside of the cell or periplasm. [68] However, in many photosynthetic bacteria, the plasma membrane is highly folded and fills most of the cell with layers of light-gathering ...