synthesis

1. SONU SAINI
ARUN PATEL
MSC ABT

2. Polysaccharides
Simply known as glycans.
Consists of repeating units of monosaccharides(hundreds
and thousands) held together by glycosidic bonds.
Linear and branched polymers.
They are primarliy concerned with two important functions-
structural and storage of energy.

3. Types of polysaccharides
Mainly two types :
Homopolysaccharides :
 which on hydrolysis yield only a single type of
monosaccharides.
 They are named based on the nature of the monosaccharide
unit.
 some are serve as the storage forms of monosaccharides that
are used as fuel; starch and glycogen.
 some are serve structural element in plant cell walls and
animal exoskeleton ; cellulose and chitin
Heteroplysaccharides :
 Which on hydrolysis yield a mixture of a few monosaccharides
or their derivates. E.g
 Mucopolysaccharides
 Hyluronan

4. Multiple
monomer
types,
branched
Homopolysaccharides
Unbranched Branched
Heteropolysaccharides
Two
monomer
types,
unbranched

5. Example of homopolysaccharides
Starch:
 used for energy storage in plants
complete hydrolysis yields only D-Glucose
Amylose –
composed of continuous, unbranched chains of as many as
4000 D-glucose units joined by alpha-1,4-glycosidic bonds

6. Amylopectin –
contains chains of as many as 10,000 D-glucose units joined
by alpha-1,4-glycosidic bonds
new chains of 24-30 units are started by alpha-1,6-glycosidic
bonds

7. Glycogen
acts as the energy-reserve carbohydrate for animals
it is branched polysaccharide containing approximately 106
glucose units joined by alpha-1,4 and alpha-1,6-glycosidic
bonds

8. Cellulose
most widely distributed plant skeletal polysaccharide
 is a linear polysaccharide of D-glucose units joined by beta-
1,4-glycosidic bonds

9. structure

10. GLUCONEOGENESIS
 Synthesis of glucose from noncarbohydrate precursors.
 This pathway shares six enzymes with the Embden-Meyerhof
pathway.
 Four reactions are catalyzed by enzymes that are specific for
gluconeogenesis.
 Gluconeogenic pathway used in many microorganisms.
 Four enzymes catalyzing irrversible reactions that are different
from those found in the Embden-Meyerhof pathway (EMP).

11. Glucose-6-phosphatase
Fructose-1,6-bisphosphatase
glucose Gluconeogenesis
Pi
H2O
glucose-6-phosphate
Phosphoglucose Isomerase
fructose-6-phosphate
Pi
H2O
fructose-1,6-bisphosphate
Aldolase
glyceraldehyde-3-phosphate + dihydroxyacetone-phosphate
Triosephosphate
Isomerase
(continued)

12. Glyceraldehyde-3-phosphate
Dehydrogenase
Phosphoglycerate Kinase
Enolase
PEP Carboxykinase
glyceraldehyde-3-phosphate
NAD+
+ Pi
NADH + H+
1,3-bisphosphoglycerate
ADP
ATP
3-phosphoglycerate
Phosphoglycerate Mutase
2-phosphoglycerate
H2O
phosphoenolpyruvate
CO2 + GDP
GTP
oxaloacetate
Pi + ADP
HCO3

+ ATP
pyruvate
Pyruvate Carboxylase
Gluconeogenesis
Summary of
Gluconeogenesis
Pathway:
Gluconeogenesis
enzyme names in
red.
Glycolysis enzyme
names in blue.

13. Gluconeogenesis:
 2 pyruvate + 2 NADH + 4 ATP + 2 GTP 
glucose+ 2 NAD+ + 4 ADP + 2 GDP + 6 Pi

14. Biosynthesis of polysaccharides
 Nucleoside diphosphate sugars play a central role in the
synthesis of polysaccharides such as starch and glycogen..
 Biosynthesis is not simply a direct reversal of catabolism.
 During the synthesis of glycogen and starch in bacteria and
protist, ADP-glucose is formed from glucose-1 phosphate and
ATP.
 It then donate glucose to the end of growing glycogen and
starch
ATP + glucose 1-phosphate ADP-glucose + PPi
(glucose)n + ADP -glucose (glucose)n+1 + ADP

15. Starch biosynthesis is growing
from reducing end

16. Plant cell wall
biosynthesis
 Plant cell wall is made
of cellulose microfibrils,
which is consisted of
about 36 chains of
cellulose, a polymer of
b(14)glucose.

17. Cellulose biosynthesis
 Cellulose is
synthesized by
terminal complexes
or rosettes, consisting
of cellulose synthase
and associated
enzymes.

18. Terminal complex (rosette)
p.777

19. Cellulose synthase
 Cellulose synthase has not been isolated in its active
form, but from the hydropathy plots deduced from its
amino acid sequence it was predicted to have eight
transmembrane segments, connected by short loops
on the outside, and several longer loops exposed to the
cytosol.

20. Initiation of new
cellulose chain
synthesis
 Glucose is transferred
from UDP-glucose to a
membrane lipid
(probably sitosterol) on
the inner face of the
plasma membrane.
p.776

21. New cellulose
chain synthesis (1)
 Intracellular cellulose synthase adds
several more glucose residues to the
first one, in (b14) linkage, forming
a short oligosacchairde chain
attached to the sitosterol (sitosterol
dextrin).

22. New cellulose chain
synthesis (2)
 Next, the whole sitosterol dextrin
flips across to the outer face of
the plasma membrane, where
most of the polysaccharide chain
is removed by endo-1,4-b-
glucanase.

23. New cellulose chain
synthesis (3)
 The dextrin primer
(removed from
sitosterol by endo-1,4-
b-glucanase) is now
(covalently) attached
to another form of
cellulose synthase.

24. New cellulose chain synthesis (4)
 The UDP-glucose used for
cellulose synthesis is
generated from sucrose
produced from
photosynthesis, by the
reaction catalyzed by
sucrose synthase (this
enzyme is wrongly named).

25. New cellulose chain synthesis (5)
 The glucose associated
with UDP is a-linked.
 Its configuration will be
converted by
glycosyltransferases so the
product (cellulose) is b-
linked.

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