Chemistry of carbohydrates polysaccharides part 3 B heteroglycans. To teach Ist year medical students. Chemistry of carbohydrates Part-1 Monosaccharides Part-2 Disaccharides Part -3A Homoglycans Part-3B Heteroglycans

1. Chemistry of Carbohydrates
Polysaccharides
Part – 3B Heteroglycans
V.S.RAVI KIRAN

2. V.S.RAVIKIRAN, MSc.,
Department of Biochemistry,
ASRAM Medical college,
Eluru-534005.AP, India.
vsravikiran2013@gmail.com

3. HETEROGLYCANS
• These are polysaccharides containing more than one type of sugar
residues.
• Examples are: Agar, Agarose

4. Agar
• It is prepared from sea weeds. It contains galactose, glucose and
other sugars.
• It is dissolved in water at 100ºC, which upon cooling sets into a gel.
Agar cannot be digested by bacteria and hence used widely as a
supporting agent to culture bacterial colonies.
• Agar is used as a supporting medium for immunodiffusion and
immunoelectrophoresis.

5. Agarose
• Agarose is made up of galactose combined with 3,6-anhydrogalactose
units;
it is used as matrix for Electrophoresis.

6. MUCOPOLYSACCHARIDES
• Mucopolysaccharides or glycosamino glycans (GAG) are
heteropolysaccharides, containing uronic acid and amino sugars.
• Acetylated amino groups, sulfate and carboxyl groups are also
generally present.
• Because of the presence of these charged groups, they attract water
molecules and so they produce viscous solutions.

7. MUCOPOLYSACCHARIDES
• Mucopolysaccharides in combination with proteins form
mucoproteins.
• Examples of mucopolysaccharides are hyaluronic acid, heparin,
chondroitin sulfate, dermatan sulfate and keratan sulfate.

8. MUCOPOLYSACCHARIDES
• Mucopolysaccharides are excreted in urine in abnormal amounts in
the group of lysosomal storage disorders known as
mucopolysaccharidoses

9. MUCOPOLYSACCHARIDES
• They can be detected by 2D gel electrophoresis techniques; some
mucopolysaccharides can also be detected by simple urine screening
tests like CPC test, Cetavlon test and Alcian blue staining.

10. Hyaluronic acid
• It is present in connective tissues, tendons, synovial fluid and vitreous
humor. It serves as a lubricant in joint cavities.
• It is composed of repeating units of N-Acetyl-glucosamine → beta-1,
4-Glucuronic acid → beta-1-3-N-Acetyl glucosamine and so on.

11. Heparin
• It is an anticoagulant widely used when taking blood in vitro for
clinical studies.
• It is also used in vivo in suspected thromboembolic conditions to
prevent intravascular coagulation.
• It activates antithrombin III, which in turn inactivates thrombin, factor
X and factor IX.

12. Heparin
• Heparin is present in liver, lungs, spleen and monocytes.
• Commercial preparation of heparin is from animal lung tissues.

13. Heparin
• It contains repeating units of sulphated glucosamine → alpha-1, 4-L-
iduronic acid → and so on. Idose is the 5th epimer of glucose.
Iduronic acid is the oxidized form of idose. Sulfated heparin or
heparin sulfate is also present in tissues.
Sulfated glucosamine-
alpha-1, 4-iduronic acid.
Repeating units in
heparin

14. Chondroitin Sulfate
• It is present in ground substance of connective tissues widely
distributed in cartilage, bone, tendons, cornea and skin.

15. Chondroitin Sulfate
• It is composed of repeating units of glucuronic acid → beta-1,3-N-
acetyl galactosamine sulfate → beta-1, 4 and so on.
D-glucuronic acid-beta-1,
3-N-acetyl galactosamine-
4 sulfate
(units of chondroitin
sulfate)

16. Keratan Sulfate
• It is the only GAG, which does not contain any uronic acid.
• The repeating units are galactose and N-acetyl glucosamine in beta
linkage.
• It is found in cornea and tendons.

17. Dermatan Sulfate
• It contains L-iduronic acid and N-acetyl galactosamine in beta-1, 3
linkages.
• It is found in skin, blood vessels and heart valves.

18. Repeating units in various polysaccharides
are summarized in Box

19. GLYCOPROTEINS AND MUCOPROTEINS
• When the carbohydrate chains are attached to a polypeptide chain it
is called a proteoglycan.
• If the carbohydrate content is less than 10%, it is generally named as
a glycoprotein.
• If the carbohydrate content is more than 10% it is a mucoprotein.

20. GLYCOPROTEINS AND MUCOPROTEINS
• They are seen in almost all tissues and cell membranes.
• About 5% of the weight of the cell membrane is carbohydrates;
the carbohydrate groups cover the entire surface of the cell
membrane, they are called glycocalyx.
• Functions include their role as enzymes, hormones, transport
proteins, structural proteins and receptors.

21. GLYCOPROTEINS AND MUCOPROTEINS
• Glycophorin is the major membrane glycoprotein of erythrocytes.
• The protein is transmembrane (spans the whole thickness of the
membrane), with polypeptide chain is seen both inside and outside
the membrane.
• Carbohydrate chains are attached to the amino terminal portion,
outside the cell surface.

22. GLYCOPROTEINS AND MUCOPROTEINS
• The oligosaccharide chains of glycoproteins are composed of varying
numbers of the following carbohydrate residue:
Glucose (Glu); mannose (Man); galactose (Gal); N-acetyl
glucosamine (GluNAc); N- acetyl galactosamine (GalNAc); arabinose
(Ara); Xylose (Xyl); L-fucose (Fuc) and N-acetyl neuraminic acid
(NANA).

23. GLYCOPROTEINS AND MUCOPROTEINS
• Carbohydrate group is attached to proteins either as O-glycosidic
linkages or as N-glycosidic linkages.
• The O-glycosidic linkage is GalNAc to serine or threonine residues of
usual protein; however, galactose is added to hydroxylysine residues
of collagen.
• The N-glycosidic linkages are made by addition of carbohydrate
group to nitrogen atom of asparagine or glutamine residues of
proteins.

24. Common Sugar Substitutes
• Acesulfame-Potassium (Ace K)
• Acesulfame-Potassium (Ace K)is made from aceto acetic acid. It is
200 times more sweet than sugar; but calorie content is negligible. It
is present in artificial sweeteners, carbonated drinks, pharmaceutical
products. It has a slightly bitter aftertaste. Unlike aspartame,
acesulfame K is stable under heat, allowing it to be used in baking, or
in products that require a long shelf life.

25. Common Sugar Substitutes
• Aspartame
• Aspartame is made from aspartic acid and phenyl alanine, both are amino
acids. (Aspartame is the methyl ester of a phenylalanine/ aspartic acid
dipeptide). It is 200 times more sweet than sugar. Calorie content is 4 kcal
per gram. Under strongly acidic or alkaline conditions, aspartame may
generate methanol by hydrolysis. Aspartame is immediately metabolized to
phenylalanine, aspartic acid and methanol. Aspartame is not suitable for
people with phenyl ketonuria.

26. Common Sugar Substitutes
• Saccharin is made from anthranilic acid. It is 300 times sweeter than
sugar. Calorie content is nil.
• Sucralose is made from sucrose or table sugar. Sucralose is
approximately 600 times as sweet as sucrose (table sugar), twice as
sweet as saccharin, and 3.3 times as sweet as aspartame. Calorie
content is nil.

27. Common Sugar Substitutes
Sodium cyclamate (Sodium cyclohexyl sulfamate)
• Sodium cyclamate (Sodium cyclohexyl sulfamate) is 30–50 times sweeter
than sugar. It is less expensive than most sweeteners and is stable under
heating.
• The 10:1 cyclamate : saccharin mixture is found to increase the incidence
of bladder cancer in rats. Its sale is banned in the United States. However,
Cyclamate is approved as a sweetener in over 55 countries.

28. Common Sugar Substitutes
• Saccharin (Benzoic sulfimide)
• Saccharin (Benzoic sulfimide) is an artificial sweetener, but has an
unpleasant bitter or metallic aftertaste, especially at high concentrations.
• It is used to sweeten products such as drinks, candies, medicines, and
toothpaste. Although saccharin has no food energy, it can trigger the
release of insulin in humans and rats, apparently as a result of its taste. It is
not banned anywhere in the world.

29. Common Sugar Substitutes
• Erythritol
• Erythritol is a natural sugar alcohol. It occurs naturally in fruits and
fermented foods. It is 60–70% as sweet as table sugar yet it is almost
non-caloric, does not affect blood sugar, does not cause tooth decay.
In the body, erythritol is absorbed, and then for the most part
excreted unchanged in the urine.

30. Common Sugar Substitutes
• Xylitol
• Xylitol is found in the fibers of many fruits and vegetables, including
various berries, corn husks, oats, and mushrooms.
• Xylitol is roughly as sweet as sucrose with only two-thirds the food energy.
• Xylitol is a safe sweetener for people with diabetes that would not impact
insulin levels.

31. Common Sugar Substitutes
• Sugar substitutes can be used in the initial phase of a dieting plan for
an obese child.
• Children, unless diabetic, should avoid them.

32. Dietary Fiber
• Dietary fiber is contributed by the unavailable carbohydrates in the
diet.
• Several different types of dietary fiber have been found in different
types of food items.
• They contribute the bulk and assist in normal bowel movements.

33. Dietary Fiber
• Cellulose, hemicellulose, pectin, alginates and gums are the usual
glycans which form dietary fiber.
• Of these cellulose, a homoglycan made of glucose is found in bran,
flour and tubers.

34. Dietary Fiber
• Hemicellulose is a mixture of glycans; pentosans made of xylose or
arabinose and hexans (mannans, galactans and polyuronic acids).
These are mainly found in whole grains and brans.

35. Dietary Fiber
• Pectins are mixtures of homoglycans found in fruits like apples and
berries. They are made of galacturonic acid and arabinose.
• Gums and alginates are found in legumes and oatmeal and are made
of polymannuronic acid.

36. Bacterial Cell Wall
• Major constituents of prokaryotic (bacterial) cells are
heteropolysaccharides, consisting of repeating units of N-acetyl
muramic acid (NAM) and N-acetyl glucosamine (NAG).
• This polysaccharide provides mechanical strength.

37. Bacterial Cell Wall
• Synthesis of this complex polysaccharide is blocked by penicillin.
• This inhibition is responsible for the bactericidal action of penicillin.

38. Bacterial Cell Wall
• Penicillin was discovered by Sir Alexander Fleming in 1928. Later,
Ernst Chain isolated and purified penicillin. The first clinical trial with
penicillin was conducted by Howard Florey in 1940. All the three were
awarded Nobel prize in 1945.
Alxander
Fleming
NP 1945
1881–1955
Ernst
Chain
NP 1945
1906–1979
Howard
Florey
NP 1945
1898–1968

39. THANK YOU
The end of carbohydrate chemistry