It describes the cell wall and its components and their structures in detail including cellulose, hemicellulose and pectin in detail.

1. PLANT BIOCHEMISTRY
Cell Wall and its composition
By: Mridhu Sharma,
Lecturer at JU

3. • Plant cell is surrounded
by rigid cell wall.
• It has large central sap
vacuole.
• Plant cells lack centrioles
and centrosome.
• Simpler units of golgi
apparatus called
dictyosomes.

4. Primary cell wall:
• It is the first formed cell wall.
• Formed outside the
meristematic cells and
parenchymatous cells.
• Is thin with 1-3µm thickness.

5. Tertiary cell wall:
• It is the formed beneath
secondary cell wall.
• It consits of cellulose along with
hemicellulose.
• The cells are cemented by middle
lamella consisting of pectin.
Secondary cell wall:
• It is the formed between
meristamatic cells and protoplasm.
• Is consists of three concentric layers
(S1, S2 and S3).
• The 2° C.W. consists of compactly
arranged microfibrils of cellulose.
• S3 layer is inner layer that is
flat spiral.
• S2 layer has microfibrillar
angle of 10-20°
• S1 layer is outermost having
microfibrillar angle of 50°

6. • Cellulose is linear, unbranched,
water insoluble polymer made up
of 2000-14000 D-glucose joined
by β 1→4 linkage.
• It has flattened ribbon like
structure (each ribbon is 1-7 µm
long).
• It has 40-70 glucan chains
held by intermolecular
hydrogen bonds.
• It is supercoiled around the cell
to permit cell elongation.

7. Hemicellulose are short heteropolymers of various monosccharides such as
arabinose, xylose, mannose, galactose, glucose and uronic acid.
Some of the hemicellulose go under the name of xylans, glucomannans,
galactomannans and xyloglucans.

8. It has a main chain
made of polymer of
Xylopyranose residues
linked by β 1→4
linkage, which are
attached to L-
arabinofuranose, D-
glucuronic acid, 4-O-
methyl- D-glucuronic
acid and D- galatose.

9. Glucomannans are
polymers of glucose
and mannose residues
linked by β 1→4
linkage.

10. Xyloglucans have a
backbone of β 1→4
linkage glucose units
with side chains of α-
1,6-xylosyl residues
and other branches
consisting xylose,
galactose, fucose and
arabinofuranose units.

11. • Pectin is mixture of polymers such as
D-galacturonic acid connected by α1→4 glycosidic linkage.
• Free carboxyl groups in adjacent chains are linked by Ca2+ and Mg2+ ions.
• In the absence of these ions the pectin is soluble compound.
• Ca2+ and Mg2+ salt of pectin forms an amorphous gel and hence used in
making gels and jams.
α1→4
glycosidic
linkage

12. • Elastin occurs in tissues of all flowering
plants.
• For plant cell to grow, the very rigid
cell wall has to be loosened.
• The hydrogen bonds between
cellulose microfibrills and crosslinking
polysaccharides are broken down by
elastin.