# Phospholipid --- **Phospholipids** are a type of [[lipids]] wiht a [[phosphate]] attached. They have a [[polar and nonpolar|hydrophilic]] head region and a [[polar and nonpolar|hydrophobic]] tail region—making them amphipathic. They are incredibly important biologically for their property of being able to form [[#Phospholipids Bilayers|phospholipid bilayers]]. Phospholipids are synthesized in the [[endomembrane system|smooth ER]] when two [[fatty acids]] undergo a [[hydrolysis and condensation reactions|condensation reactions]] with a molecule, similar to triglycerides. ## Structure There are two main components of a phospholipid are the hydrophilic head and the two hydrophobic tails. ![[phospholipid.png]] ### Head & Tail The **hydrophilic head** of a phospholipid is a [[lipids#Glycerol|glycerol]] with a [[functional group#Biologically Important Functional Groups|phosphate]] on one end and the tail on the other end. The presence of the phosphate is what gives it it's hydrophilic nature. The **hydrophobic tail** is made up of two [[fatty acids]]. The fatty acids are connected to the head via an [[plasma membrane#Ester Linkage|ester linkage]] in bacteria and eukaryotes, and an [[plasma membrane#Ether Linkage|ether linkage]] in archaea. ## Phospholipids Bilayers **Phospholipid bilayers** are special arrangements of phospholipids in biology that form [[plasma membrane|plasma membranes]] for cells. To make these layers, the lipids are arranged such that their polar heads face away from each other and their nonpolar tails face inwards. There is no water in between the layers. ![[bilayer.png]] Because they have to be special, instead of this general arrangement of phospholayers, [[archaea]] have a special single layer type of phospholipids. ## Liposome & Micelles **Liposomes** and **micelles** are different structures made from lipids. There is no water inside the micelles, because the inside is the hydrophobic region. One example of micelle-like structure is a [[lipoprotein]]. ![[liposome and micelle.png]] ___