Editing Biological membrane (section)

=== Lipids ===
The biological membrane is made up of lipids with hydrophobic tails and hydrophilic heads.<ref name=":0">{{Cite book|title = Fundamentals of Biochemistry: Life at the Molecular Level (4 ed.)|last = Voet|first = Donald|publisher = Wiley|year = 2012|isbn = 978-1118129180}}</ref> The hydrophobic tails are hydrocarbon tails whose length and saturation is important in characterizing the cell.<ref name=":4">{{Cite journal|title = Lipid and phospholipid fatty acid composition of plasma, red blood cells, and platelets and how they are affected by dietary lipids: a study of normal subjects from Italy, Finland, and the USA|journal = The American Journal of Clinical Nutrition|date = 1987|pmid = 3812343|pages = 443–455|volume = 45|issue = 2|first1 = R. M.|last1 = Dougherty|first2 = C.|last2 = Galli|first3 = A.|last3 = Ferro-Luzzi|first4 = J. M.|last4 = Iacono|s2cid = 4436467|doi = 10.1093/ajcn/45.2.443}}</ref> Lipid rafts occur when lipid species and proteins aggregate in domains in the membrane. These help organize membrane components into localized areas that are involved in specific processes, such as signal transduction.

Red blood cells, or erythrocytes, have a unique lipid composition. The bilayer of red blood cells is composed of cholesterol and phospholipids in equal proportions by weight.<ref name=":4" /> Erythrocyte membrane plays a crucial role in blood clotting. In the bilayer of red blood cells is phosphatidylserine.<ref name=":5">{{cite journal|title = Exposure of platelet membrane phosphatidylserine regulates blood coagulation|journal = Progress in Lipid Research|date = 2003|pmid = 12814644|pages = 423–438|volume = 42|issue = 5|first = Barry R.|last = Lentz|doi=10.1016/s0163-7827(03)00025-0}}</ref> This is usually in the cytoplasmic side of the membrane. However, it is flipped to the outer membrane to be used during blood clotting.<ref name=":5" />