1. Carbohydrates
Polysaccharides
Dr. Nikhat Siddiqi

2. Contents Polysaccharides – Classification Homoglycans Heteroglycans
Dr. Nikhat Siddiqi

3. Joining of monosaccharides
Monosaccharides can be joined to form disaccharides, oligosaccharides, and polysaccharides.
Important disaccharides include lactose (galactose + glucose), sucrose (glucose + fructose), and maltose (glucose + glucose).
Important polysaccharides include branched glycogen (from animal sources) and starch (plant sources) and unbranched cellulose (plant sources); each is a polymer of glucose.
The bonds that link sugars are called glycosidic bonds. These are formed by enzymes known as glycosyltransferases.
Dr. Nikhat Siddiqi

4. Naming glycosidic bonds
Glycosidic bonds between sugars are named according to the numbers of the connected carbons, and also with regard to the position of the anomeric hydroxyl group of the sugar involved in the bond.
Dr. Nikhat Siddiqi

5. Naming glycosidic bonds
If this anomeric hydroxyl is in the α configuration, the linkage is an α-bond.
If it is in the β configuration, the linkage is a β-bond.
Lactose, for example, is synthesized by forming a glycosidic bond between carbon 1 of β-galactose and carbon 4 of glucose. The linkage is, therefore, a β(1→4) glycosidic bond.
Dr. Nikhat Siddiqi

6. Polysaccharides Polysaccharides are also called as glycans.
Made up of large number of monosaccharides linked by glycosidic linkages.
Smaller glycans are called as oligosaccharides (10-15 monomers) found attached to popypeptides in glycoproteins and some glycolipids.
Found in membrane and secretary proteins.
Dr. Nikhat Siddiqi

7. Polysaccharides - Classification
Homoglycans
Polysaccharides
Heteroglycans
Dr. Nikhat Siddiqi

8. Polysaccharides - Classification
Structural Polysaccharides
Polysaccharides
Storage Polysaccharides
Dr. Nikhat Siddiqi

9. Homoglycans Found in starch, glycogen, cellulose and chitin.
Starch, glycogen, cellulose give D-glucose when hydrolysed.
Starch –energy storage molecule in plants.
Glycogen –energy storage molecule in animals.
Chitin – component of exoskeleton of insects, cell wall of fungi, yields glucose derivative N-acetylglucosamine when hydrolyzed.
Dr. Nikhat Siddiqi

10. Starch (Storage Polysacchardes)
Significant source of carbohydrate in human diet.
Source- potatoes, rice, wheat, corn.
Amylose
Starch
Amylopetin
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11. Amylose
Composed of long, unbranched chains of S-glucose residues that are linked by (1,4) glycosidic bonds.
Have one reducing end in which the ring can open to form free aldehyde group with reducing properties.
Dr. Nikhat Siddiqi

12. Amylose
Contains several thousand glucose residues has molecular weight 150,000 to 600,000.
Linear amylose molecule forms tight helices.
Gives blue colour with iodine due to interaction between iodine molecules and the helically arranged glucose rsidues.
Dr. Nikhat Siddiqi

13. Amylopectin
is branched polymer containing (1,4) and (1,6)glycosidic linkages.
The (1,6) points may occur every 20 to 35 residues and prevent helix formation.
Dr. Nikhat Siddiqi

14. Starch digestion begins in the mouth where the salivary enzyme - amylase initiates hydrolysis of glycosidic bonds.
Digestion continues in the small intestine where pancreatic -amylase hydrolyzes all the (1,4) glycosidic bonds except the branch points.
The products of - amylase maltose, trisaccharide maltotriose and  limit dextrin.
Dr. Nikhat Siddiqi

15. Starch - Structure
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16. Glycogen (Storage Polysaccharides)
Storage carbohydrate in vertebrates.
Found in liver and skeletal muscle.
Structure similar to amylopectin except that it has more branch point possibly at every fourth glucose residue.
Dr. Nikhat Siddiqi

17. Glycogen-Structure
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18. Glycogen- Structure
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19. Cellulose (Structural Polysaccharides)
Polymer of D-glucopyranose residues linked by (1,4) glycosidic bonds. Unbranched
Structural polysaccharide in plants.
Pairs of unbranched cellulose molecules may contain as many as 12,000 glucose units each held together by hydrogen bonding to form sheet like strips called microfibrils. These structures are found in primary and secondary cell walls of plants.
Dr. Nikhat Siddiqi

20. Cellulose makes up dietary fiber.
The ability to digest cellulose is found in microorganism which contain the enzyme cellulase.
Cellulose can be hydrolyzed to its constituent glucose units by microorganisms that inhabit the digestive tract of termites and ruminants.
Cellulose makes up dietary fiber.
Paper, wood, textiles are some of cellulose containing products.
Dr. Nikhat Siddiqi

21. Cellulose - Structure
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22. Chitin (Structural Polysaccharide)
Chitin is an unbranched polymer of N-Acetyl-D-glucosamine.
It is found in fungi and is the principal component of arthropod and lower animal exoskeletons, e.g., insect, crab, and shrimp shells.
It may be regarded as a derivative of cellulose, in which the hydroxyl groups of the second carbon of each glucose unit have been replaced with acetamido (-NH(C=O)CH3) groups.
Dr. Nikhat Siddiqi

23. Chitin - Structure
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24. Polysaccharides
Heteroglycans
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25. Heteroglycans
High molecular weight carbohydrate polymers that contain more than one kind of monosaccharides.
Major classes found in animals are N and O-linked glycans attached to proteins.
Dr. Nikhat Siddiqi

26. Glycosaminoglycans (GAGs)
Glycosaminoglycans (GAGs) are large complexes of negatively charged heteropolysaccharide chains.
They are generally associated with a small amount of protein, forming proteoglycans, which typically consist of over 95% carbohydrate.
Dr. Nikhat Siddiqi

27. Glycosaminoglycans (GAGs)
Glycosaminoglycans have the special ability to bind large amounts of water, thereby producing the gel-like matrix that forms the basis of the body's ground substance, which, along with fibrous components such as collagen, make up the extracellular matrix.
The viscous, lubricating properties of mucous secretions also result from the presence of glycosaminoglycans, which led to the original naming of these compounds as mucopolysaccharides.
Dr. Nikhat Siddiqi

28. Structure of Glycosaminoglycans
Glycosaminoglycans are long, unbranched, heteropolysaccharide chains generally composed of a repeating disaccharide unit [acidic sugar–amino sugar]n.
Dr. Nikhat Siddiqi

29. Structure of Glycosaminoglycans
The amino sugar is either D-glucosamine or D-galactosamine, in which the amino group is usually acetylated, thus eliminating its positive charge.
The amino sugar may also be sulfated on carbon 4 or 6 or on a nonacetylated nitrogen.
The acidic sugar is either D-glucuronic acid or its carbon-5 epimer, L-iduronic acid.
Dr. Nikhat Siddiqi

30. Structure of Glycosaminoglycans
A single exception is keratan sulfate, in which galactose rather than an acidic sugar is present.
These acidic sugars contain carboxyl groups that are negatively charged at physiologic pH and, together with the sulfate groups, give glycosaminoglycans their strongly negative nature.
Dr. Nikhat Siddiqi

31. Some monosaccharide units found in glycosaminoglycans.
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32. Functions of GAGs
Because of their large number of negative charges, these heteropolysaccharide chains tend to be extended in solution.
They repel each other, and are surrounded by a shell of water molecules.
When brought together, they “slip” past each other, much as two magnets with the same polarity seem to slip past each other.
This produces the “slippery” consistency of mucous secretions and synovial fluid.
Dr. Nikhat Siddiqi

33. Functions of GAGs---cont
When a solution of glycosaminoglycans is compressed, the water is “squeezed out” and the glycosaminoglycans are forced to occupy a smaller volume.
When the compression is released, the glycosaminoglycans spring back to their original, hydrated volume because of the repulsion of their negative charges.
This property contributes to the resilience of synovial fluid and the vitreous humor of the eye.
Dr. Nikhat Siddiqi

34. Classification of the glycosaminoglycans
The six major classes of glycosaminoglycans are divided according to monomeric composition, type of glycosidic linkages, and degree and location of sulfate units.
Dr. Nikhat Siddiqi

35. Structure and distribution of glycosaminoglycans (GAGs).
Dr. Nikhat Siddiqi

36. Hyaluronic Acid
Hyaluronate molecules may consist of as many as 25,000 disaccharide units, with molecular weights of up to 107.
Hyaluronates are important components of the vitreous humor in the eye and of synovial fluid, the lubricant fluid of joints in the body.
Dr. Nikhat Siddiqi

37. The chondroitins and keratan sulfate are found in tendons, cartilage, and other connective tissue, whereas dermatan sulfate, as its name implies, is a component of the extracellular matrix of skin.
Heparin, with the highest net negative charge of the disaccharides shown, is a natural anticoagulant substance.
Dr. Nikhat Siddiqi

38. Proteoglycans High carbohydrate content (about 95%).
Occur on cell surfaces or are secreted into extracellular matrix.
Dr. Nikhat Siddiqi

39. Structure of proteoglycans
All of the glycosaminoglycans, except hyaluronic acid, are found covalently attached to protein, forming proteoglycan monomers.
Dr. Nikhat Siddiqi

40. Structure of proteoglycan monomers
A proteoglycan monomer found in cartilage consists of a core protein to which the linear glycosaminoglycan chains are covalently attached.
These chains, which may each be composed of more than 100 monosaccharides, extend out from the core protein, and remain separated from each other because of charge repulsion.
The resulting structure resembles a “bottle brush”. In cartilage proteoglycan, the species of glycosaminoglycans include chondroitin sulfate and keratan sulfate.
Dr. Nikhat Siddiqi

41. “Bottle-brush” model of a cartilage proteoglycan monomer.
A proteoglycan monomer found in cartilage consists of a core protein to which the linear glycosaminoglycan chains are covalently attached.
Dr. Nikhat Siddiqi

42. Linkage region of glycosamino-glycans
Linkage between the carbohydrate chain and the protein: This linkage is most commonly through a trihexoside (galactose-galactose-xylose) and a serine residue, respectively.
An O-glycosidic bond is formed between the xylose and the hydroxyl group of the serine.
Dr. Nikhat Siddiqi

43. Proteoglycan aggregates
The proteoglycan monomers associate with a molecule of hyaluronic acid to form proteoglycan aggregates. The association is not covalent, but occurs primarily through ionic interactions between the core protein and the hyaluronic acid. The association is stabilized by additional small proteins called link proteins .
Dr. Nikhat Siddiqi

44. Proteoglycans
Proteoglycans consist of a protein core (brown) and one or more covalently attached glycosaminoglycan chains ([blue].
Dr. Nikhat Siddiqi

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46. Examples of proteoglycans
Examples include syndecans, glycipcans and affrecans
The syndecans are a class of heparan sulfate and chondroitin sulfate containing proteoglycans in which the core protein is a transmembrane protein.
Aggregans is found in cartilage.
Dr. Nikhat Siddiqi

47. Mucopolysaccharidoses
The mucopolysaccharidoses are hereditary disorders (1:25,000 births) that are clinically progressive.
They are characterized by accumulation of glycosaminoglycans in various tissues, causing varied symptoms, such as skeletal and extracellular matrix deformities, and mental retardation.
Mucopolysaccharidoses are caused by a deficiency of any one of the lysosomal hydrolases normally involved in the degradation of heparan sulfate and/or dermatan sulfate .
Dr. Nikhat Siddiqi

48. Functions of Proteoglcans
Organizing extracellular matrix.
Membrane bound syndecans, glycipcans bind to specific signal molecules like growth factors involved in cell cycle regulation.
Because of their vast number of polyionic GAG chains, the aggrecans trap large volume of water.
Give strength, flexibility to cartilage and tensile strength to collagen fibers.
Dr. Nikhat Siddiqi

49. Glycoproteins
Proteins that are linked covalantly to carbohydrates through N- or 0- linkages.
Carbohydrate content varies from 1% to more than 85% of total weight.
Carbohydrates include monosaccharides or disaccharides such as those attached to collagen or branched oligosaccharides found on plasma glycoproteins.
Dr. Nikhat Siddiqi

50. Polysaccharides Two broad classed viz., N-linked and O-linked.
N-linked are attached to polypeptides by an N-glycosidic bond with the side chain amide group of amino acid asparagine.
O-linked are attached to polypeptides by side chain hydroxyl group of the amino acid serine or threonine in a polypeptide chain or the hydroxyl group of membrane lipids.
Dr. Nikhat Siddiqi

51. Polysaccharides linked to polypeptides
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52. Differences between Glycoproteins and Protoglycans
They differ from the proteoglycans (which might be considered a special case of glycoproteins) in that the length of the glycoprotein's carbohydrate chain is relatively short (usually 2–10 sugar residues in length, although they can be longer).
Dr. Nikhat Siddiqi

53. Differences between Glycoproteins and Protoglycans ---cont
In addition, whereas glycosaminoglycans have diglucosyl repeat units, the carbohydrates of glycoproteins do not have serial repeats.
The glycoprotein carbohydrate chains are often branched instead of linear, and may or may not be negatively charged.
Dr. Nikhat Siddiqi

54. Glycoproteins contain highly variable amounts of carbohydrate.
For example, immunoglobulin IgG, contains less than 4% of its mass as carbohydrate, whereas human gastric glycoprotein (mucin) contains more than 80% carbohydrate.
Dr. Nikhat Siddiqi

55. Functions of glycoproteins
Membrane-bound glycoproteins participate in a broad range of cellular phenomena, including cell surface recognition (by other cells, hormones (insulin receptors), and viruses),
cell surface antigenicity (such as the blood group antigens),
as components of the extracellular matrix and
of the mucins of the gastrointestinal and urogenital tracts, where they act as protective biologic lubricants.
Dr. Nikhat Siddiqi

56. Functions of Glycoproteins
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57. Sialic acid residues are responsible for high viscosity and luricating properties of saliva.
Cellular adhesion eg selectins (transient cell-cell interaction), intergins (cell attachment to components of extracellular matrix) and cadherins (calcium dependent binding of cells to each other within tissue.
Dr. Nikhat Siddiqi

58. Dr. Nikhat Siddiqi