Transcript System_Structure

System Structure
Somerville et al. 2004
Figure 1 shows an electron microscope picture
of the outer cell walls of pea (Pisum sativum).
Cell walls are composed of compounds called
polysaccharides which create a network of
stable fibers within the wall.
What is a Polysaccharide?
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A polysaccharide is a chain, created by simple
sugars called monosaccharides. Common
monosaccharides are glucose and fructose, found in most
sweets. They join together by glycosidic bonds, created by
dehydration reactions between the -OH group of one
monosaccharide to the –H of another. These form the
three most important aspects to the cell wall.
Cellulose
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Cellulose is a polymer of the monosaccharide glucose. It forms 180
degree bond angles of the glycosidic bonds, making it a very sturdy,
aiding in the structure of the leaf itself.
Chains of cellulose form
together to create a
microfibril, a collection
of chains of cellulose
combined to form an
even more sturdy
structure. Collections of
these microfibrils form
macrofibrils which then
form the cellulose
fibers.
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Hemicellulose
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Hemicelluloses are polysaccharides made from these monomers,
which hydrogen bond to the surface of the cellulose fibrils.
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Pectins
Pectins are the acidic polysaccharides found in
the parts of fruits and vegetables such as peels
and apple pommace. (www.lsbu.ac.uk/water/hypec.html)
It is marketed for making jam and
jelly, as well as different types of
jelly beans! 
Pectins are hydrophobic
polysaccharides that attract
water to the cell. This makes
the cell more pliable, which is
necessary for wall expansion.
Pectins primarily form the
middle lamella in the cell
wall, which join adjacent
cells. (Raven, Everett, and Eichhorn 2005)
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Homogalacturonan (HG) is the
most simple of pectins, as
discussed in the Somerville
paper.
But How Do They All Fit In The Cell Wall?
A diagram of
a plant cell wall,
as shown in the
Somerville et. al.
article.
Somerville et. al.
According to Somerville
et.al, the main force for
the structure of the cell
wall is from the hydrogen
bonding of the hemicellulose
to the cellulose microfibrils.
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