Essay On Cell Membranes

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The cell membranes of archaea are unique among the three domains of life. Although archaea also possess a phospholipid bilayer, similar to bacteria and eukaryotes, the bilayer itself differs greatly in chemical composition. The first striking difference is the use of L-glycerol instead of D-glycerol, along with having an ether linkage linking the tail to the head; whereas eukaryotes and bacteria have an ester linkage. However the main difference in archaea membranes in the isoprenoid chain replacing the fatty acid tail of a conventional phospholipid bilayer. These isoprene chains also contain branching methyl side chains, which can interact with the plasma membrane in surprising ways.
The first difference is the chirality of glycerol. Bacteria and eukarya possess D-glycerol, while archaea have L-glycerol. These terms are in fact historical, their actual names being sn-glycerol-3-phosphate and sn-glycerol-1-phosphate; respectively. These names also encompass the
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The methyl radical can bend back along the isoprenoid chain and bond with another atom creating a carbon ring. It can polymerise smaller cyclopropane or large cyclohexane rings. This cyclic compound is often found in archaeal extremophiles, thus it is thought to strengthen the plasma membrane, allowing them to survive in extreme conditions. The methyl radicals themselves can form hydrogen bonds between the individual phospholipids, thereby strengthening the lipid as a whole. Finally, in some species of archaea the phospholipid bilayer is replaced by a monolayer, the two isoprene tails fuse with the opposite two on the other side of the membrane. This creates a single molecule with two hydrophilic ends and a hydrophobic middle region. This makes the plasma membrane more rigid and makes the archaea able to withstand harsh

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