Biomedical Engineering Reference
In-Depth Information
Cross section of a plant cell
Cytoplasm
Cell wall
Cell
membrane
Amylosplast
Vacuole
Centrosome
Nucleus
Rough ER
Nucleolus
Smooth ER
Nuclear
membrane
Ribosomes
Chloroplast
Golgi body
Mitochondrion
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Figure 1.20
A plant cell. In vascular plants cellulose is
synthesized at the cell membrane (also called the plasma
membrane) by rosette terminal complexes. After [129].
Hydrophilic
head
Hydrophilic head
(OCH
2
CH
2
)
m
OH
Hydrophobic tail
(CH
2
)
n
Hydrophobic
tail
CH
3
(a)
(b)
Figure 1.21
An example of an amphiphilic molecule: (a)
symbolic representation and (b) chemical structure (alkyl
polyoxyethylene).
and lipophilic (
fat-liking)
properties. Such a compound is called
amphiphilic
or
amphipathic
. Common amphiphilic substances are soaps and detergents.
An amphiphilic molecule is composed of two different parts: hydrophobic tail
and hydrophilic head. The tail is composed of one or more hydrocarbon chains, and
the head is composed of chemical groups with high affinity to water, Figure 1.21.
Phospholipids, a class of amphiphilic molecules, are the main components
of biological membranes. When the phospholipids are immersed in an aqueous
solution, they arrange themselves into bilayers, by positioning their polar groups
toward the surrounding aqueous medium, and their lipophilic chains toward the
inside of the bilayer, defining a nonpolar region between the two polar ones.
