Cell Membrane Constituents
T h e se lipids contain a long unsatu rated hydrocarbon chain am ino alchohol know n a s s p h in g o s in e :
A derivative ot sphingosine, in which a fatty a d d is linked by an am ide linkage, is c e r a m ld e :
T he product obtained w hen th e alchohol hydroxyl group of sphingosine is esterified with phosphorylcholine is
s p h in g o m y e lin .The conform ations of phosphatidylcholine a n d sphingom yelin a re similiar.
G ly c o s p h in g o lip ld s (c e re b ro s id e s )
A derivative of ceram ide th at contains a m onosaccharide unit (either glucose o r g alacto se) linked in a B-glycosidic linkage is a cerebroside.
T h ese neutral hprds occu r m ost abundantly in th e brain an d myelin sh eath of nerves. T h e sp ed fic galactocerebroside, ph ren o sin e contains
a z-hydroxy-24-carbon fatty acid residue. Following is a structure of a glucocerebroside.
membrane viscosity. Thus, the lipid composition of the
membrane at physiological temperatures can have signif-
icant effects on fluidity and permeability. Some correla-
tion appears to exist between the concentrations of sphin-
gomyelin and cholesterol in different membranes. Plasma
membranes (e.g., red blood cells and myelin sheaths) are
rich in both; the inner membrane of mitochondria contains
Membrane proteins show considerable mobility in the
plane of the bilayer (lateral motion). There is no evidence
that proteins migrate from one side of the bilayer to the
other. The frequency of reorientation of lipid components
(flip-flop migration) is extremely slow or nonexistent, for
Artificial membrane systems (
) have in-
creased our understanding of the dynamic nature of lipid