Editing Lipid bilayer (section)

===Surface chemistry===
While lipid tails primarily modulate bilayer phase behavior, it is the headgroup that determines the bilayer surface chemistry. Most natural bilayers are composed primarily of [[phospholipid]]s, but [[sphingolipids]] and [[sterol]]s such as [[cholesterol]] are also important components.<ref>{{cite book|last1=Alberts |first1=Bruce |title=Molecular Biology of the Cell |date=2017 |publisher=Garland Science |isbn=9781317563747 |chapter-url=https://books.google.com/books?id=2xIwDwAAQBAJ |chapter=Chapter 10: Membrane Structures}}</ref> Of the phospholipids, the most common headgroup is [[phosphatidylcholine]] (PC), accounting for about half the phospholipids in most mammalian cells.<ref name=Yeagle1993/> PC is a [[zwitterion]]ic headgroup, as it has a negative charge on the phosphate group and a positive charge on the amine but, because these local charges balance, no net charge.<ref name="Ko 2015">{{cite journal |last=Ko |first=Du Young |last2=Patel |first2=Madhumita |last3=Jung |first3=Bo Kyoeng |last4=Park |first4=Jin Hye |last5=Jeong |first5=Byeongmoon |title=Phosphorylcholine-Based Zwitterionic Biocompatible Thermogel |journal=Biomacromolecules |volume=16 |issue=12 |date=14 December 2015 |doi=10.1021/acs.biomac.5b01169 |pages=3853–3862}}</ref>

Other headgroups are also present to varying degrees and can include [[phosphatidylserine]] (PS) [[phosphatidylethanolamine]] (PE) and [[phosphatidylglycerol]] (PG). These alternate headgroups often confer specific biological functionality that is highly context-dependent. For instance, PS presence on the extracellular membrane face of [[erythrocyte]]s is a marker of cell [[apoptosis]],<ref name=Fadoka1998>{{cite journal |vauthors=Fadok VA, Bratton DL, Frasch SC, Warner ML, Henson PM |title=The role of phosphatidylserine in recognition of apoptotic cells by phagocytes |journal=Cell Death Differ. |volume=5 |issue=7 |pages=551–62 |date=July 1998 |pmid=10200509 |doi=10.1038/sj.cdd.4400404 |doi-access=free }}</ref> whereas PS in [[growth plate]] vesicles is necessary for the [[nucleation]] of [[hydroxyapatite]] crystals and subsequent bone mineralization.<ref name=Anderson2005>{{cite journal |vauthors=Anderson HC, Garimella R, Tague SE |title=The role of matrix vesicles in growth plate development and biomineralization |journal=Frontiers in Bioscience |volume=10 |issue= 1–3|pages=822–37 |date=January 2005 |pmid=15569622 |url=http://www.bioscience.org/2005/v10/af/1576/fulltext.htm |doi=10.2741/1576}}</ref><ref name=Eanes1987>{{cite journal |vauthors=Eanes ED, Hailer AW |title=Calcium phosphate precipitation in aqueous suspensions of phosphatidylserine-containing anionic liposomes |journal=Calcif. Tissue Int. |volume=40 |issue=1 |pages=43–8 |date=January 1987 |pmid=3103899 |doi=10.1007/BF02555727 |s2cid=26435152 }}</ref> Unlike PC, some of the other headgroups carry a net charge, which can alter the electrostatic interactions of small molecules with the bilayer.<ref name=Kim1991>{{cite journal |vauthors=Kim J, Mosior M, Chung LA, Wu H, McLaughlin S |title=Binding of peptides with basic residues to membranes containing acidic phospholipids |journal=Biophysics Journal |volume=60 |issue=1 |pages=135–48 |date=July 1991 |pmid=1883932 |pmc=1260045 |doi=10.1016/S0006-3495(91)82037-9 |bibcode=1991BpJ....60..135K}}</ref>