Essential Cell Biology 5th edition

75
LIPID AGGREGATES
Fatty acids have a hydrophilic head
and a hydrophobic tail.
surface film
POLYISOPRENOIDS
Long-chain polymers
of isoprene
In water, they can form either a surface
film or small, spherical micelles.
micelle
O
O – P O –
O
Their derivatives can form larger aggregates held together by hydrophobic forces:
Triacylglycerols form large, spherical
fat droplets in the cell cytoplasm.
Phospholipids and glycolipids form self-sealing lipid
bilayers, which are the basis for all cell membranes.
200 nm
or more
4 nm
OTHER LIPIDS
Lipids are defined as water-insoluble
molecules that are soluble in organic
solvents. Two other common types of lipids
are steroids and polyisoprenoids. Both are
made from isoprene units.
CH 3
C CH CH 2
CH 2 isoprene
STEROIDS
Steroids have a common multiple-ring structure.
OH
HO
cholesterol—found in many cell membranes
O
testosterone—male sex hormone
GLYCOLIPIDS
Like phospholipids, these compounds are composed of a hydrophobic
region, containing two long hydrocarbon tails, and a polar region,
which contains one or more sugars. Unlike phospholipids, there is
no phosphate.
galactose
H OH
H
O
C C CH sugar
2
C C
H H C NH
O
a simple
glycolipid
dolichol phosphate—used
to carry activated sugars
in the membraneassociated
synthesis of
glycoproteins and some
polysaccharides
Panel 2.05b