Classification of polysaccharides, gluconeogenesis and glucogenolysis.

G. D. RUNGTA COLLEGE OF SCIENCE & TECHNOLOGY, KOHKA, BHILAI.
BY:-
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Dr. ARUNIMA KARKUN
ASST. PROFESSOR

CLASSIFICATION OF POLYSACCHARIDES, GLUCONEOGENESIS
GLYCOGENOLYSIS
 INTRODUCTION
 WHAT ARE POLYSACCHARIDES?
 GENERAL CHARACTERSTICS OF
POLYSACCHARIDES
 CLASSIFICATION OF POLYSACCHARIDES
1. Homopolysaccharides
2. Heteropolysaccharides
 ROLE OF POLYSACCHARIDES
 GLUCONEOGENESIS
 GLYCOGENOLYSIS
 SUMMARY
 REFERENCES
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CLASSIFICATION OF POLYSACCHARIDES
 All organisms utilize carbohydrates  important
biomolecules.
 Nutrition: “carbos” are more than just starch and sugar.
 The term carbohydrate is derived from the french word:
“hydrate de carbone.”
 compounds composed of C, H, and O.
 empirical formula: (CH2O)n.
 Defination:- carbohydrate defined as
polyhydroxyaldehyde or ketone which produce
them on hydrolysis.
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 FUNCTION OF CARBOHYDRATES
 Most abundant dietary source of energy (4 cal/g) for all organisms.
 Participate in the structure of cell membrane & cellular functions.
 Structural components of many organisms, include the fiber (cellulose) of
Plants, exoskeleton of some insects.
 Storage of energy to meet the immediate energy demands of the body.
 CLASSIFICATION OF CARBOHYDRATES
I. MONOSACCHARIDES- glucose, fructose.
I. OLIGOSACCHARIDES
• Di, tri, tetra, penta, upto 9 or 10
• Most important are the disaccharides-lactose, sucrose.
II. POLYSACCHARIDES OR GLYCANS
• Homopolysaccharides-starch, glycogen, cellulose
• Heteropolysaccharides
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CONT.

 Generally called glycans.
 Contains a number of monosaccharide units linked by
glycosidic bonds.
 CHARACTERISTICS:
 Polymers (MW from 200,000).
 White and amorphous products (glassy)
 Not sweet.
 Not reducing; do not give the typical aldose or
ketose reactions).
 Form colloidal solutions or suspensions.
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POLYSACCHARIDES

POLYSACCHARIDES
HOMOPOLYSACCHARIDES HETROPOLYSACCHARIDES

Divided into two broad groups:
(i) Homopolysaccharides-
 Contains only one type of monomer.
 On hydrolysis, they yield only one type of monosaccharide.
Examples: Starch, cellulose, glycogen
(ii) Heteropolysaccharides-
 Contain two or more types of monomers.
 On hydrolysis, they yield mixture of monosaccharides.
Examples: hyaluronic acid, chondriotin sulphate, heparin,
and mureins.
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Fig. no 1

1. STARCH
• Two forms: amylose , amylopectin.
• 1,4-a-D-glucopyranose polymer.
• Function: plant glucose/energy storage.
• Hydrolysis  glucopyranose.
• Easily digested by mammals.
• Natural starches contain 10-20% amylose and 80-90%
amylopectin.
a. Amylose - unbranched α (1-4 )
• 200 to 20 000 glucose units.
• Water soluble(15-20%).
• Stained blue by iodine.
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Homopolysaccharides-
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b. Amylopectin - branched
α (1-4 ) + α (1-6 )
 Up to million glucose
units.
 Water insoluble
amylopectin(80-
82%).
 Stained red-brown by
iodine.
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-
STRUCTURE NO .1
STRUCTURE NO .2
CONT.

2. GLYCOGEN
 The glucose storage polymer in animals, is similar in
structure to amylopectin
 But glycogen has more a(16) branches.
 The highly branched structure permits rapid glucose
release from glycogen stores, e.g., in muscle during
exercise.
 The ability to rapidly mobilize glucose is more essential
to animals than to plants
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S H O
OH
H
OHH
OH
CH2OH
H
O H
H
OHH
OH
CH2OH
H
O
HH H O
O
H
OHH
OH
CH2
H
H H O
H
OHH
OH
CH2OH
H
OH
HH O
O
H
OHH
OH
CH2OH
H
O
H
O
1 4
6
H O
H
OHH
OH
CH2OH
H
H H O
H
OHH
OH
CH2OH
H
H
O
1
OH
3
4
5
2
glycogen
CONT.
STRUCTURE NO .3

3. CELLULOSE - nonbranched ß (1-4 )
• Insoluble, chemically very resistant.
• Major structural material of plants, wood, cotton.
• It is a major constituent of fiber.
• Cellulose is totally absent in animal.
• Composed of ß - D-glucose units linked by ß (1-4 ) glycosidic
bonds.
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STRUCTURE NO . 4
CONT.

4.CHITIN
N-acetyl-D-glukosamine a ( 1-4 )
• Structural polysaccharide of exoskeleton of invertebrates (in complex with proteins
and/or CaCO3)
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S 5. PECTIN
D-galakturonic acid a (1-4)
• Methylesters
often side chains containing other
monosaccharides.
• Present in small fruits, plants.
STRUCTURE NO.5
.
STRUCTURE NO..6
CONT

2.HETEROPOLYSACCHARIDES
 It is composed of a mixture of monosaccharides.
 On hydrolysis, they yield a mixture of monosaccharides.
 HETEROPOLYSACCHARIDES - are further
classified into two types:
A. NEUTRAL SUGARS.
B. MUCOPOLYSACCHARIDES .
A. NEUTRAL SUGARS.
 This group Includes some hemicellulose, some gums,
mucilages & pectic substances.
 Give more than one type of sugar units on hydrolysis &
sometimes non-sugar components .
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B. MUCOPOLYSACCHARIDES .
 Mucopolysaccharides are heteroglycans made up of
polysaccharides made up of repeating units of sugar
derivatives, namely amino sugars & uronic sugar.
 Commonly known as Glycosaminoglycans (GAG).
 Mucopolysaccharides are essential components of tissue
structure.
 Some Mucopolysaccharides are found in combination with
proteins to form Mucoproteins or mucoids or proteoglycans .
 Mucopolysaccharides include hyaluronic acid ,heparin ,
dermatan sulfate, keratan sulfate.

1.HYALURONATE (Hyaluronan) or Hyluronic acid.
 It is a glycosaminoglycan with a repeating
disaccharide consisting of 2 glucose derivatives, glucuronate
(glucuronic acid) & N-acetyl-glucosamine.
 The glycosidic linkages are ß (1-3) & ß (1-4).
 Hyaluronidase is an enzyme present in high concentration in
testes, seminal fluid, in certain snake & insects that breaks ß(1-
4) linkages.
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H O
H
H
OHH
OH
COO
H
H O
OH H
H
NHCOCH3H
CH2OH
H
OO
D-glucuronate
O
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4
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6
1
23
4
5
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N-acetyl-D-glucosamine
hyaluronate
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MUCOPOLYSACCHARIDES
STRUCTURE NO..7

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2. KERATAN SULFATE
 It is a heterogeneous GAG with a variable sulfate content, besides small
amounts of mannose, fructose, sialic acid etc.
 It is essentially consists of alternating units of D- galactosamine and
N-acetylglucasamine .
 They are present in cartilage, bone, cornea, nail, hoofs, claws.
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STRUCTURE NO.8
CONT.

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3.HEPARIN
 Heparin is an anticoagulant (prevents blood clotting) that occurs in blood,
lung, liver, kidney, spleen etc.
 Made in mast cell & released into the blood.
 Heparin is composed of alternating units of N-sulfo D-glucosamine 6-
sulfate & glucoronate 2-sulfate,
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STRUCTURE NO.9
CONT.

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 ROLE OF POLYSACCHARIDES
TABLE NO .1

GLUCONEOGENESIS
 Definition: the biosynthesis of glucose primarily from pyruvate and its
precursors.
 The major substrates/precursors for gluconeogenesis are lactate, pyruvate,
glucogenic amino acid, propionate & glycerol.
 The liver is the major location for gluconeogenesis (about 1kg glucose
synthesized everyday).
 Gluconeogenesis occurs mainly in the Cytosol, although some precursors are
produced in the Mitochondria.
 This is essential cycle for the survival of humans and other animals.
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GLUCONEOGENESIS
 Gluconeogenesis closely resembles the reversed pathway of glycolysis,
although it is not the complete reversal of glycolysis.
 Essentially, 3(out of 10) reactions of glycolysis are irreversible.
 The 7 reactions are common for both glycolysis & Gluconeogenesis.
 The 3 irreversible steps of glycolysis are catalysed by the enzymes, namely
hexokinase , phosphofructokinase and pyruvate kinase.
 These 3 stages- bypassed by alternate enzymes specific to Gluconeogenesis
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GLUCONEOGENESIS
21CYCLE NO.1
CONT.

GLUCONEOGENESIS
 These 3 stages- bypassed by alternate enzymes specific to Gluconeogenesis are below:-
1. Conversion of pyruvate to phosphophenol-pyruvate:
 This takes place in two steps –
a) Pruvate carboxylase is a biotin-dependent mitochondrial enzyme that converts
Pruvate to oxaloacetate in presence of ATP & CO2.
b) In the cytosol, phosphoenolpyruvate carboxykinase converts oxaloacetate to
phosphoenolpyruvate.
2. Conversion of fructose 1,6-biphosphate to fructose 6-phosphate:
 Phosphophenolpyruvate undergoes the reversal of glycolysis until fructose
1,6-biphosphate is produced.
3. Conversion of Glucose 6-phosphate to Glucose:
 Glucose 6-phosphate catalyses the conversion of Glucose 6-phosphate to
Glucose.
 Glycolysis & Gluconeogenesis are both spontaneous.
 If both pathways were simultaneously active in a cell, it would constitute a
"futile cycle" that would waste energy .
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GLUCONEOGENESIS
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SEQEUENTIAL REACTIONS OF GLUCONEOGENESIS
CHART NO.2
CONT.

GLUCONEOGENESIS
 Overall summary of Gluconeogenesis for the conversion of
pyruvate to glucose is shown below:-
Glycolysis:
glucose + 2 NAD+ + 2 ADP + 2 Pi 
2 pyruvate + 2 NADH + 2 ATP.
Gluconeogenesis:
2 pyruvate + 2 NADH + 4 ATP + 2 GTP +2H+ 
glucose + 2 NAD+ + 4 ADP + 2 GDP + 6 Pi +6H +
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GLUCONEOGENESIS
IMPORTANCE OF GLUCONEOGENESIS :-
 Brain, central nervous system, erythrocytes, testes & kidney medulla are
dependent on glucose for continuous supply of energy.
 In fasting even more than a day gluconeogenesis must occur to meet the basal
requirements of the body.
 Glucose is the only source that supplies energy to the skeletal muscle , under
anaerobic conditions.
 Certain metabolites produced in the tissues accumulate in the blood e.g
lactate ,glycerol etc gluconeogenesis effectively clears them from blood.
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GLYCOGENOLYSIS
 DEFINATION:-The degradation of stored glycogen in the liver and
muscle constitutes GLYCOGENOLYSIS.
 The pathways for the synthesis and degradation of glycogen are not possible
are not reversible.
 An independent set of enzymes present in the cytosol carry out glycogenolysis.
 Glycogen is degraded by breaking α-1,4- & α-1,6-glycosidic bonds.
 A good coordination & regulation of glycogen synthesis & its degradation are
essential to maintain the blood glucose levels.
 Glycogenesis & glycogenolysis are , respectively, controlled by the enzymes
glycogen synthase & glycogen phosphorylase.
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GLYCOGENOLYSIS
2.ACTION OF GLYCOGEN PHOSPHORYLASE:-
 The α-1,4-glycosidic bonds are cleaved sequentially by the enzyme glycogen to
yield glucose 1-phosphate.This process is called phosphorolysis.
 The glycogen so formed is known as limit dextin which cannot be further
degraded by phosphorylase.
2. ACTION OF DEBRANCHING ENZYME:
 The branches of glycogen are cleaved by two enzyme activities present on a single
polypeptide called debranching enzyme, hence it is a bifunctional enzyme.
 Amylo α-1,4-glycosidase breaks the α-1,6-bond at the branch with a single glucose
residue and release a free glucose.
3.FORMATION OF GLUCOSE 6-PHOSPHATE AND GLUCOSE:
 Through the combined action of glycogen phosphorylase and debranching enzyme
glucose 1-phosphate & free glucose in a ratio of 8:1 are produced .
 Glucose 1-phosphate is converted to glucose 6-phosphate by the enzyme
phosphoglucomutase.
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GLYCOGENOLYSIS
 Glycogen is the storage form of glucose.
 The degradation of glycogen (glycogenolysis) in muscle
meets the immediate fuel requirements.
 On the other hand the liver glycogen maintains the blood
glucose level.
 Enzymes defects in synthesis or the degradation of glycogen
leads to storage disorders.
 Von Gierke’s disease is due to the defect in the enzyme
glucose 6- phosphatase .
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SUMMARY
 Carbohydrates are the polyhydroxyaldhyde or ketones or compounds which
produce them on hydrolysis .
 Carbohydrates are broadly classified into three groups:-
MONOSACCHARIDES,OLIGOSACCHARIDES,POLYSACCHARIDES.
 Polysaccharides are the polymers of monosaccharides on their derivative, held
together by glycosidic bonds.
 Polysaccharides are broadly classified into two groups:-
(A)Hompolysaccharides (B)Heteropolysaccharides
 The biosynthesis of glucose primarily from pyruvate and its precursors is
known as gluconeogenesis.
 The degradation of stored glycogen in the liver and muscle constitutes
glycogenolysis.
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CLASSIFICATION OF POLYSACCHARIDES , GLUCONEOGENESIS,
GLYCOGENOLYSIS
 Polysaccharides play important role in structure & storage for plants.
 Polysaccharides are also help in cell envelope development in bacteria.
 Polysaccharides provides exoskeleton in spiders & insects.
 In fasting even more than a day gluconeogenesis must occur to meet the
basal requirements of the body.
 Glucose is the only source that supplies energy to the skeletal muscle ,
under anaerobic conditions.
 Certain metabolites produced in the tissues accumulate in the blood e.g
lactate ,glycerol etc gluconeogenesis effectively clears them from blood.
 Glycogenolysis supplies energy to muscles & other body parts.
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CLASSIFICATION OF POLYSACCHARIDES , GLUCONEOGENESIS,
GLYCOGENOLYSIS
ALBERT L. LEHNINGER YEAR -2005 BIOCHEMISTRY,
2ND EDITION, FREEMAN
PUBLICATION.
L. NELSON & M. COX YEAR -2009 PRINCIPLES OF
BIOCHEMISTRY, 5TH
EDITION,STUTTGAT
PUBLICATION.
J. L. JAIN YEAR -2010 PRINCIPLES OF
BIOCHEMISTRY,
6TH EDITION,S.CHAND
PUBLICATION.
U.SATYANARAYANA ,
U.CHAKRAPANI
YEAR -2010 BIOCHEMISTRY,
6TH EDITION,UPPALA
PUBLICATION.
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Classification of polysaccharides, gluconeogenesis and glucogenolysis.

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