3. DISACCHARIDES
•
•
•
Most common among oligosaccharides
two monosaccharide units (similar or
dissimilar) held by glycosidic bonds
properties – water soluble, sweet to taste
REDUCING
NON REDUCING
MALTOSE,LACTOSE,ISOMALTOSE,CELLOBI
SUCROSE,TREHAL
OSE
6. MALTOSE
•
•
•
•
Digestion of starch by amylase,germinating seeds,
malt
Action of maltase or dilute acid on maltose gives
glucose units
Fermented by yeasts
PROPERTIES:
Reducing sugar, soluble and sweet taste
Sunflower shaped osazones
Mutarotation
Exhaustive methylation of all free –OH
group,followed by hydrolysis of glycosidic linkage
gives 2,3,4,6-tetra-O-methyl-D-glucose and 2,3,6-triO-methyl-D-glucose
8. LACTOSE
•
•
•
In milk
Action of intestinal lactase on lactose gives glucose
and galactose
PROPERTIES:
Reducing sugar
Powder puff or hedgehog or badminton ball shaped
osazone
Not very soluble and not so sweet
dextrorotatory
At body temperature exists as an equilibrium mixture
of α and β forms in 2:3
11. SUCROSE
•
•
•
•
•
In sugar cane,sugar beet,pineapple,carrot
roots
Major carbohydrate in photosynthesis (in
roots,tuber,seeds)
Most abundant among naturally occuring
sugars
Distinct advantage:storage and transport
forms
Action of Intestinal sucrase on sucrose gives
glucose and fructose
12. SUCROSE
PROPERTIES
Non reducing
No osazone formation
Very soluble and very sweet
Specific sucrose test
USE
Sweetening agent in food industry
13. INVERSION OF SUCROSE
•
•
•
•
•
Dextrotatory sucrose (+66.5˚) on hydrolysis
becomes levorotatory
Equimolar mixture of glucose and fructose is
invert sugar
Honey contains invert sugar (sweeter than
sucrose)
β-D-glucopyranose
α -D-glucopyranose
+18.7 ˚
+112.2 ˚
Sucrose sucrase
β -D-fructofuranose
β -D-fructopyranose
-133 ˚
α -D-fructopyranose
-21˚
14. ISOMALTOSE, GENTIOBIOSE
ISOMALTOSE -
Glucose + glucose
α(1 → 6)
partial hydrolysis of glycogen and starch gives it
oligo-1,6-glucosidase in intestinal juice hydrolyses
GENTIBIOSE -
β (1 → 6)
glucose +glucose
16. CELLOBIOSE
6 CH 2OH
H
4
OH
5
6
O
H
OH
H
5
H
1
O
CH 2OH
4
O
H
OH
H
3
H
2
OH
3
cellobiose
H
H
2
OH
1
H
OH
Virtually no taste
Not fermented by yeast
Obtained by hydrolysis of cellulose
Indigestible by humans
Β(1→ 4) linkage is represented as zigzag but one glucose is
actually flipped over relative to other
17. LACTULOSE
A ketodisaccharide
• Fermented by intestinal bacteria
• Used in osmotic laxative, in hepatic
encephalopathy
α-D-galactopyranosyl-(1 → 4)-β-Dfructofuranose
•
18. TRISACCHARIDES
•
RAFFINOSE
in sugar beets
• O-α-D-galactopyranosyl-(1→6)-0-α-D- glucopyranosyl (1→2)-β-D-fructofuranoside
• MELEZITOSE
in sap of some coniferous trees
O-α-D-glucopyranosyl-(1→3)-O-β-D-fructofuranosyl-(2 → 1)-α-Dglucopyranoside
20. POLYSACCHARIDES(GLYCANS)
Repeat units of monosaccharides or their
derivatives,held by glycosidic bonds
Relatively or totally insoluble,tasteless
LINEAR
BRANCHED
24. STARCH
•
•
•
•
•
Most important dietary source of man and
animals
Carbohydrate reserve of plants
In potato,tapioca,rice,wheat
Deposited in form of granules in cytoplasm
STARCH Acid hydrolysis
GLUCOSE
25. AMYLOSE
Amylose
α(1 → 4)
Not soluble in water
Forms hydrated micelles
Gives blue colour with iodine
Helical coil with 6 glucose/turn
Amylopectin
α(1→4) but branching points are
α(1→ 6)
Most abundant in plants
Gives red violet colour with iodine
26. AMYLASES
Two types-α and β
Both hydrolyse only α- glycosidic bonds
α- amylase = α(1→4)-glucan-4glucanhydrolase
β-amylase = α(1→4)-glucan-4-maltohydrolase
Debranching enzyme- α (1→6)-glucosidase or
α (1→6)- glucan-6-glucanhydrolase
27. BREAKDOWN PRODUCTS OF STARCH
STARCH
AMYLOPECTIN
BLUE
VIOLET
ERYTHRODEXTRIN
RED
ACHRODEXTRIN
NO
MALTOSE
NO
28. GLYCOGEN
Main storage polysaccharide of animal cell
Abundant in liver and skeletal muscle
Also in plants that do not have chlorophyll
Animal starch
Immediate source of energy
Dextrorotatory
Not readily soluble in water and forms opalascent solution
Not destroyed by hot strong KOH or NaOH
With iodine gives deep red colour
29. GLYCOGEN
Glycogen is used as energy source,glucose units are removed one at a time from
non reducing ends
Glucose is not stored in monomeric form
Starch and glycogen are heavily hydrated
30. DEXTRAN
Polymer of D-glucose
Synthesized by leuconostoc mesenterides
Dental plaque
Synthetic dextrans
Branched polysaccharide of D-glucose
Branching at 1 → 2, 1 → 3, 1 → 4 or 1 → 6
Plasma volume expander
31. INULIN
D-fructose residues in β(2→1)
In dahlia,garlic,onion,dandelion
White, tasteless powder
Levorotatory
No dietary importance in humans
Used for estimation of body water
volume(ECF),assesing kidney functions
through means of GFR
34. CELLULOSE
Schematic of arrangement of
cellulose chains in a microfibril.
Every other glucose molecule is flipped over other due to β linkages
Parallel orientation is favoured by intermolecular hydrogen bond
X-ray diffraction of cellulose shows bundles of parallel chains to form fibrils
Not digested by mammals
35. CELLULOSE
Most abundant structural polysaccharide in
plants
Cotton fibers are pure cellulose
Insoluble in water
Complete hydrolysis
D-glucose
Strong acids
CELLULOSE
partial hydrolysis
Cellobiose
Exhaustive methylation
2,3,6-tri-O-methyl
glucose
