# The Domain Archaea --- **Archaea** is one of the three [[domains of life|domains]] of life, and one of the two groups of [[prokaryote|prokayotic]] organisms. They are best known from their living in spectacularly inhospitable environments, but they don't necessarily have to live in those types of places. Although they appear similar to [[bacteria]] in many ways, they are actually *more* different from bacteria than they are from *[[eukaryote|eukaryotes]]*. Note how in the image below the line splits *between* bacteria and archaea. ![[three-domain classification.png]] ### Archaeal Cell Wall: Pseudopeptidoglycan Archaea have a **[[cell wall#Cell Wall in Archaea|cell wall]]** that is similar to a bacteria's cell wall, made up of a carbohydrate called [[peptidoglycan#Pseudopeptidoglycan|pseudopeptidoglycan]]. ### Membranes The [[plasma membrane]] of an archaea has several unique [[plasma membrane|features]] compared to bacteria and eukaryotes. Firstly they are not made of [[phospholipid#Phospholipids Bilayers|phospholipid bilayers]] as in other organisms, but rather a **monolayer**, where the tails of the phospholipids are covalently bonded in the "middle" to form one whole, double-headed phospholipid. These are much more structurally robust, and better able to withstand the harsh environments in which archaea tend to live. Additionally, the [[plasma membrane#Phospholipid Tails|tails of the phospholipids]] branch off at points. Additionally they use [[plasma membrane#Esters vs Ethers|ether linkages]] between the phospholipid head and tails, as opposed to ester linkages. ![[archaea phospholipid.png]] ### Archaeal Immune Systems The same type of [[bacterial immune system|immune system]] found in bacteria is found in archaea as well—which is specially designed for fighting off viruses. ___