The document discusses carbohydrates, focusing on their classification into polysaccharides, homopolysaccharides, and heteropolysaccharides, emphasizing their structure and hydrolysis. It covers functions of carbohydrates including energy provision and protein sparing, as well as the regulation of blood glucose, and disorders like diabetes mellitus. Key details about various polysaccharides, their digestive processes, and health implications are also highlighted.

1. Chemistry of Carbohydrates
(polysaccharides)
Dr Gurjinder Singh
Department of Biochemistry,

2. Polysaccharides
 Consist of repeating units of monosaccharide units or
derivatives ( > 10) held together by glycosidic bond.
 Two types-
A.Homopolysaccharides-
• On hydrolysis single type of monosaccharides. Glucans are
polymers of Glucose & Fructosans are polymers of Fructose.
• B. Heteropolysaccharides-
• On hydrolysis yield a mixture of few monosaccharides or their
derivatives.

3. Polysaccharides

4. Homopolysaccharides
• Starch
• Carbohydrate reserve of plants & most important dietary source for man.
• Consist of D-Glucose units held together with α-glycosidic bonds &
known as glucosan or glucans.
• Two polysaccharide components- water soluble amylose(15-20℅) &
water insoluble amylopectin(80-85℅).
• Amylose- unbranched chain with 200-1000 D-Glucose units held by α(1
→ 4) bond.
• Amylopectin- branched chain with both α(1 → 4) & α(1 → 6) bonds.

7. Acid hydrolysis of starch
• Acid hydrolysis gives following intermediate products:
• Starch Soluble starch amylodextrin Erythrodextrin
acrodextrin Maltose Glucose
• Dietary starch is hydrolyzed by Salivary and pancreatic -amylase.
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• These enzymes act on -1,4 glycosidic linkages to give the final
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products of dextrins,maltose and isomaltose.
• Dextrins are intermediate products of starch found in honey,
toasted bread and partially hydrolyzed starch.

8. Dextrin
• Homoglycans ,water soluble food storage forms with both -1,4 and -1,6
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glycosidic linkages.
• amylodextrin, Erythrodextrin, acrodextrin are starch hydrolyzed products based
on iodine test.
• Amylodextrin , violet color
• Erythrodextrin red color,
• Acrodextrin : no color
• Breakdown products of Starch by enzyme amylase or dilute acids.
• Various intermediates in hydrolysis of Starch(identified by iodine colouration)-
Starch (blue), amylodextrin (violet), erythrodextrin (red) & acrodextrin (no colour).

9. Dextrans
• Yeast and bacterial polysaccharides produced by
microorganisms.
• Dental plaque of teeth is rich in dextran.
• They are polymers of glucose linked by -1,4 -1,6 and -1,3
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linkages.
• Used as plasma volume expanders due to high molecular
weight.
• Used in transfusions during hypovalemia as it does not easily
go out of vascular compartment .
• Used as Sephadex in chromatography.

10. .
Homopolysaccharides
• GLYCOGEN-
• Carbohydrate reserve of animals, hence called animal starch.
• Highest conc. in liver followed by muscle & brain.
• Repeating units of Glucose with α(1→4) bond & α(1→6) bond at
branching site.
• Structure similar to amylopectin with more number of branches and
more compact.

12. Homopolysaccharides
CELLULOSE-
• Occurs extensively in plants & it is totally absent in animals.
• Repeating units of β-D-Glucose linked by β(1,4) bonds.
• Not digested by mammals due to lack of enzyme that cleaves β
glycosidic bond.
• Major constituent of fiber which reduces absorption of Glucose
& cholesterol from intestine also increasing bulk of feces

13. • Unbranched linear polymer with B-1,4 linkages (300-3000
units)
• Not utilized /digested due to absence of enzyme cellulase
• On partial hydolysis it yields cellobiose similar to maltose
made up of 2 beta subunits linked by B-1,4 linkages
• Processed to produce papers and fibers

14. Homopolysaccharides
INULIN
• Polymer of Fructose i.e. Fructosan.
• Occurs in dhalia,garlic.onion.
• Used for assessment of GFR.

16. CHITIN
• N-acetyl D-Glucosamine units held together by
β(1 → 4) glycosidic bonds.
•
• It is tough protective semitransparent substance;
the principal component of arthropods.
• It is found in exoskleton of some
invertebrates. Crabs lobsters and insects.

18. HETEROPOLYSACCHARIDES OR
MUCOPOLYSACCHARIDES-
• Repeating units of amino sugars & uronic acid.
• More commonly known as Glycosaminoglycans(GAG).
• Ground substance of extracellular matrix is mainly
composed of GAGs.
• MUCOPOLYSACCHARIDES (old name) detected in
mucous membranes.
• Amino sugars are either glucosamine or galactosamine
in their N-acetylated forms.

19. Hyaluronic acid-
• Consists of repeatd alternate units of β-D-Glucronic acid and N-Acetyl D –
Glucosamine.
• Found in synovial fluid of joints & vitreous humor of eyes.
• Present in connective tissues and gel around ovum.
• Lubricant and shock absorbent in joints.
• Hyaluronidase is the enzyme which breaks this linkage & is present in testes &
seminal fluids.
• All GAG’s except Hyaluronic acid in the body are linked to core proteins, forming
proteoglycans .
• Only GAG that is unsulphated and not attached to protein
• Hyaluronidase is the enzyme plays a role in fertilization.
• It acts on hyaluronic acid present on outer coat of mammalian egg as gel, cleaves
glycosidic bonds of hyaluronic acid, enabling fertilization

21. Heparin-
• It is a polymer of L-iduronic acid 2 sulphate and N-sulpho -
D glucosamine -6 sulphate linked by β(1 ,4) glycosidic bonds
• Naturally ocouring Anticoagulant; occurs in blood, lung,
liver, kidney.
• Helps in release of lipoprotein lipase clearing lipemic
plasma.
• It prevents intravascular clotting in thromboembolisms.
• Activates antithrobin-III which inhibits conversion of
prothrombin to thrombin
• It is used to treat and prevent deep vein thrombosis and
pulmonary embolisim

22. Structure of heparin

23. Chondroitin sulfates
• Composed of β-D-Glucuronic acid and N-Acetyl D
Galactosamine 4 -sulpahte.
• Linked with β(1,3) glycosidic linkage
• Major constituent of bone, cartilage, tendons, heart valves.
• Contributes to the compressibility and weight bearing
capacity of the cartilage.
• Most abundant GAG found in the connective tissue

25. Dermatan sulfate
• Composed of repeating subunits of β-L-idouronic
acid and N-Acetyl D Galactosamine 4 –sulpahte.
• Mostly occurs in skin & sclera.
• Responsible for maintaining shape of the eyeball.
• Structural role in the matrix of connective tissue,
maintains the shape of tissue

27. Keratan sulfate
• Composed of D-Galactose and N-
Acetyl glucosamine 6 -sulpahte.
• Occurs in cornea, tendons, cartilage.
• Role in corneal transparency.

28. Structure of Keratan sulpahte

29. GAGs Composition Tissue distribution functions
Hyaluronic
acid
β- D glucuronic acid & N-
acetyl D glucosamine
Synovial fluid, joints,
connective tissue,
cartilages, Vitrous
humor of eye
Lubricant, Shock
absorber, helps in
wound healing
Chondroitin- 4
sulphate
β- D glucuronic acid & N-
acetyl D galactosamine-4
sulphate
Cartilage, tendons,
bones & joints, blood
vessel walls
Maintain structure
& shape of
tissue,also as
lubricants in skeletal
tissue
Heparin L-iduronic acid 2 sulphate
and N-sulpho - D
glucosamine -6 sulphate
Blood, lung, liver,
kidney and spleen
Anticoagulant
Dermatan
sulphate
L- iduronic acid & N-
acetyl D galactosamine 4
sulphate
Skin, Blood vessels,
heart valves, cornea
& sclera
Maintain shape of
tissues, eyeball
Keratan
sulphate
β- D Galactose & Nacetyl
D glucosamine 6 sulphate
Cartilage, cornea,
Connective tissues
Role in corneal
transperency

31. Functions Of GAGs
 Structural component. They are major components
of the extracellular matrix or ground substance.
 Have special ability to bind large amounts of
water, producing a gel like matrix which functions
as a cushion against mechanical shocks

32. Functions of GAGs
 Negatively charged glycosaminoglycans chain repel each
other, and proteoglycans occupy a very large space and
act as “molecular sieves”, determin­
ing which substances
enter and leave cells.
 They also give elasticity (resilience) to cartilage,
permitting compression and re-expansion.
 They lubricate joints.

33. Summary
• Define carbohydrates.
• Classify carbohydrates with examples.
• Mention the functions of carbohydrates
• Describe monosaccharides, disaccharides and
polysaccharides as an energy source with examples.

34. 34
Functions of Carbohydrates
1) Energy
• glucose fuels the work of most of the body’s cells
– preferred fuel of NERVOUS TISSUE (the brain, nerves) and
RED BLOOD CELLS (RBC)
• excess glucose is stored as GLYCOGEN in liver and
muscle tissue

35. 35
Functions of Carbohydrates
2) Sparing Body Protein
• if diet does not provide enough glucose, then other
sources of glucose must be found
• if carbohydrate intake < 50 - 100 g, body protein will
be used to make glucose
• an adequate supply of carbohydrate spares body
proteins from being broken down to synthesize
glucose

36. 36
Functions of Carbohydrates
3) Preventing Ketosis (Anti-ketogenic)
• carbohydrates required for the complete
metabolism of fat
• incomplete fat metabolism produces KETONES
• an adequate supply of carbohydrate (> 50 –
100 g per day) prevents KETOSIS

37. 37
Regulation of Blood Glucose
Optimal functioning of the body is dependant on
keeping levels of glucose within certain parameters.
Elevated blood glucose = Hyperglycemia
Low blood glucose = Hypoglycemia
The ENDOCRINE SYSTEM is primarily responsible for
regulating blood glucose. The two main hormones are
INSULIN and GLUCAGON.

38. 38
Regulation of Blood Glucose

39. 39
Diabetes Mellitus
• a disorder of energy metabolism due to failure of insulin to
regulate blood glucose
• results in hyperglycemia
• acute symptoms include thirst, increased urine production,
hunger
• long term consequences include increased risk of heart
disease, kidney disease, blindness, neural damage
• two forms: Type I and Type II

40. 40
Diabetes Mellitus
Type I
• accounts for about 10% of cases
• occurs when b cells of the pancreas are destroyed
– insulin cannot be synthesized
• without insulin, blood glucose levels rise because the
tissues are unable to access the glucose
• death occurs shortly after onset unless given
injections of insulin

41. 41
Diabetes Mellitus
Type II
• occurs when cells of body are unable to respond to
insulin
• called “insulin insensitivity” or “insulin resistance”
• blood glucose levels rise
• insulin secretion increases in an attempt to
compensate
– leads to hyperinsulinemia

42. 42
Hypoglycemia
• dramatic drop in blood glucose
• symptoms similar to an anxiety attack: rapid weak
heart beat, sweating, anxiety, hunger, trembling,
weakness
• RARE in healthy people
• may occur as a result of poorly managed Diabetes or
other causes:
– reactive hypoglycemia
– fasting hypoglycemia

43. THANK YOU