LECTURE 3 -CARBOHYDRATESLECTURE 3 -CARBOHYDRATES

CO 2:CO 2:

Describe, Discuss, and Describe, Discuss, and compare the classification, compare the classification, structure and function of structure and function of carbohydrates and its carbohydrates and its derivatives.derivatives.

LECTURE 3 -CARBOHYDRATESLECTURE 3 -CARBOHYDRATES

TOPICS:TOPICS:

1.1. Role & Significance of Role & Significance of CarbohydratesCarbohydrates

2.2. MonosacharidesMonosacharides

3.3. OligosacharidesOligosacharides

4.4. PolysacharidesPolysacharides

5.5. GlyconoconjugatesGlyconoconjugates

Section

Section

Section

Section

Section

Sect.1. ROLE OF CARBOHYDRATESSect.1. ROLE OF CARBOHYDRATES

As a major energy source for living As a major energy source for living organisms organisms (glucose is a principal energy source in animal and plants)(glucose is a principal energy source in animal and plants)

As a means of transporting energy As a means of transporting energy ( exp: ( exp:

sucrose in plant tissues)sucrose in plant tissues)

As a structural material As a structural material ( cellulose in plants, chitin in insects, ( cellulose in plants, chitin in insects,

building blocks of nucleotides)building blocks of nucleotides)..As a precursor for other biomolecules As a precursor for other biomolecules (purine, pyrimide) (purine, pyrimide)

Sect 1. SIGNIFICANCE OF CARBOHYDRATESSect 1. SIGNIFICANCE OF CARBOHYDRATES

Carbohydrates are the most abundant Carbohydrates are the most abundant biomolecules in nature, having a direct link biomolecules in nature, having a direct link between solar energy and the chemical bond between solar energy and the chemical bond energy in living organisms.energy in living organisms.

Source of rapid energy productionSource of rapid energy production

Structural building blocks of cellsStructural building blocks of cells

Components of several metabolic pathwaysComponents of several metabolic pathways

Recognition of cellular phenomena, such as cell Recognition of cellular phenomena, such as cell recognition and binding (e.g., by other cells, recognition and binding (e.g., by other cells, hormones, and viruses)hormones, and viruses)

Carbohydrate : compounds contains H, C & O with the Carbohydrate : compounds contains H, C & O with the comp : (CHcomp : (CH22O)O)nn (Hydrate of carbon) (Hydrate of carbon)

Carbohydrates : Carbohydrates : Consist of sugar (saccharum)Consist of sugar (saccharum)Sugars : Sugars : compound that contains alcohol & carbonyl compound that contains alcohol & carbonyl

functional groupfunctional group

Carbonyl func.group : >C=oCarbonyl func.group : >C=o

Adehyde Adehyde aldose aldose

Ketone Ketone ketose ketose

CARBOHYDRATESCARBOHYDRATES

Examples:Examples:

cellulose, chitin, cellulose, chitin, starch, glycogen, starch, glycogen, glucoaminoglycansglucoaminoglycans

disaccharidesdisaccharides GlycoproteinsGlycoproteins (bacterial cell (bacterial cell wallswalls

ClassificationClassification

Carbohydrate

Mono Mono saccharidesaccharide

OligoOligosaccharidesaccharide

PolyPolysaccharidesaccharide GlyconoconjugatesGlyconoconjugates

Glucose, fructoseRibose (aldopentose)Deoxy ribose

glycoproteins and proteoglycans

Sect2.Sect2.

MONOSACHARIDESMONOSACHARIDES

Sect. 2. MonosacharidesSect. 2. Monosacharides

Sub sections :Sub sections :2.1 Properties & classification 2.1 Properties & classification 2.2 Stereoisomers2.2 Stereoisomers2.3 Cyclic structure2.3 Cyclic structure2.4 Important Reactions2.4 Important Reactions2.5 Important monosach2.5 Important monosach2.6 2.6 glycoproteinsglycoproteins and and proteoglycansproteoglycans2.7 2.7 Monosaccharide derivatives

2.1 Monosach Properties& classification2.1 Monosach Properties& classification

Colorless, crystalline solidsSSoluble in water but insoluble in nonpolar solventsOne of the carbon atoms is double-bonded to an oxygen atom to form a carbonyl group; each of the other carbon atoms has a hydroxyl group.– Carbohydrates with an aldehyde (-CHO) functional Carbohydrates with an aldehyde (-CHO) functional

group are called group are called aldoses aldoses e.g. glyceraldehyde (CHe.g. glyceraldehyde (CH22OH-CHOH-OH-CHOH-CHOCHO))

Those with a keto group (-C=O) are Those with a keto group (-C=O) are ketosesketoses e.g.dihydroxyacetone (CH2OH-e.g.dihydroxyacetone (CH2OH-C=OC=O-CH2OH)-CH2OH)

– Classified according to the number of carbon atoms Classified according to the number of carbon atoms they containthey contain

Monosacharides : Exp. aldoses & ketosesMonosacharides : Exp. aldoses & ketoses

AldotetroseAldotrioseAldopentoses

Ketotriose Ketotetrose Ketopentose Ketohexose

Aldohexose

2.2. MONOSACCHARIDES STEREOISOMERS2.2. MONOSACCHARIDES STEREOISOMERSIsomers: same chemical formulas, different structures Conformation : the spatial arrangement of substituent groupschiral centers: asymmetric carbons, i.e carbon atom with four different substituentsEnantiomers : mirror images Stereoisomers The simplest aldose, glyceraldehyde, contains one chiral center (the middle carbon atom) and has two different optical isomers, or enantiomers

the projection in which the carbohydrate backbone is the projection in which the carbohydrate backbone is

drawn vertically with the carbonyl shown on the top.drawn vertically with the carbonyl shown on the top.

D- and L- enantiomersD- and L- enantiomers

2.3 Cyclic structure of monosacharides2.3 Cyclic structure of monosacharidesin aqueous solution, monosaccharides with five or more carbon atoms in the backbone occur predominantly as cyclic (ring) structures in which the carbonyl group has formed a covalent bond with the oxygen of a hydroxyl group along the chain.

The new chiral center in cyclic (c1) is called anomeric carbon

Pyranoses& FuranosesPyranoses& Furanoses

Pyranoses: six-membered ring compounds ( resemble pyran )Furanoses : fivemembered rings, (resemble furan)

The structure systematic names glucose & fructose become

An English chemist W.N. An English chemist W.N. Haworth gave a more accurate Haworth gave a more accurate picture of carbohydrate picture of carbohydrate structure. (Ref. P.205 of structure. (Ref. P.205 of textbook)textbook)

HAWORTH STRUCTURESHAWORTH STRUCTURES

FISHER AND HAWORTH FORMS OF SUGARFISHER AND HAWORTH FORMS OF SUGAR

SUMMARY OF SUGAR STRUCTURESSUMMARY OF SUGAR STRUCTURES

ISOMERS- compounds that have the same chemical formula e.g. ISOMERS- compounds that have the same chemical formula e.g. fructose, glucose, mannose, and galactose are isomers of each fructose, glucose, mannose, and galactose are isomers of each other having formula Cother having formula C66HH1212OO66..EPIMERS- refer to sugars whose configuration differ around one EPIMERS- refer to sugars whose configuration differ around one specific carbon atom e.g. glucose and galactose are C-4 epimers specific carbon atom e.g. glucose and galactose are C-4 epimers and glucose and mannose are C-2 epimers.and glucose and mannose are C-2 epimers.ENANTIOMERS- a special type of isomerism found in pairs of ENANTIOMERS- a special type of isomerism found in pairs of structures that are mirror images of each other. The mirror images structures that are mirror images of each other. The mirror images are termed as enantiomers and the two members are designated as are termed as enantiomers and the two members are designated as D- and L- sugar. The vast majority of sugars in humans are D-D- and L- sugar. The vast majority of sugars in humans are D-sugars.sugars.CYCLIZATION OF SUGARS- most monosaccharides with 5 or CYCLIZATION OF SUGARS- most monosaccharides with 5 or more carbon atoms are predominately found in a ring form, where more carbon atoms are predominately found in a ring form, where the aldehyde or ketone group has reacted with an alcoholic group the aldehyde or ketone group has reacted with an alcoholic group on the same sugar group to form a on the same sugar group to form a hemiacetalhemiacetal or or hemiketal hemiketal ring.ring.

PyranosePyranose ring- if the ring has 5 carbons and 1 oxygen. ring- if the ring has 5 carbons and 1 oxygen. Furanose Furanose ring- if the ring is 5-membered (4 carbons and 1 oxygenring- if the ring is 5-membered (4 carbons and 1 oxygen

2.4.IMPORTANT REACTIONS IN MONOSACCHARIDES2.4.IMPORTANT REACTIONS IN MONOSACCHARIDES

Monosaccharides undergo the following reactions :Monosaccharides undergo the following reactions :

1.1. MutarotationMutarotation2.2. OxidationOxidation3.3. ReductionReduction4.4. IsomerizationIsomerization5.5. EsterificationEsterification6.6. Glycoside formationGlycoside formation

1.1. Mutarotation – Mutarotation – alfaalfa and and betabeta forms of sugars are readily interconverted when forms of sugars are readily interconverted when dissolved in waterdissolved in water

22 Oxidation and reduction Oxidation and reduction in presence of oxidising agents, metal ions (Cu2+) and enzymes, in presence of oxidising agents, metal ions (Cu2+) and enzymes, monosacchs undergo several oxidation reactions e.g. Oxidation of monosacchs undergo several oxidation reactions e.g. Oxidation of aldehyde group (R-CHO) yields aldonic acid; of terminal CH2OH aldehyde group (R-CHO) yields aldonic acid; of terminal CH2OH (alcohol) yields uronic acid; and of both the aldehyde and CH2OH (alcohol) yields uronic acid; and of both the aldehyde and CH2OH gives aldaric acid. The carbonyl groups in both aldonic and uronic gives aldaric acid. The carbonyl groups in both aldonic and uronic can react with an OH group in the samcan react with an OH group in the sam

33 REDUCTIONREDUCTIONreduction of the aldehyde and ketone groups of monosacchs yield reduction of the aldehyde and ketone groups of monosacchs yield sugar alcohols (alditols) Sugar alcohols e.g.sorbitol, are used sugar alcohols (alditols) Sugar alcohols e.g.sorbitol, are used commercially in processing foods and pharmaceuticals. e molecule commercially in processing foods and pharmaceuticals. e molecule to form a cyclic ester lactone.to form a cyclic ester lactone.

IMPORTANT REACTIONS IN MONOSACCHARIDESIMPORTANT REACTIONS IN MONOSACCHARIDESDetailsDetails

IMPORTANT REACTIONS (Cont)IMPORTANT REACTIONS (Cont)

4.4. ISOMERIZATION ISOMERIZATION Monosaccharides undergo several types of isomerization e.g. D-glucose in Monosaccharides undergo several types of isomerization e.g. D-glucose in alkaline solution for several hours containn D-mannose and D-fructose. The alkaline solution for several hours containn D-mannose and D-fructose. The conversion of glucose to mannose is termed s conversion of glucose to mannose is termed s epimerizationepimerization. (p.208-9 of . (p.208-9 of Textbook).Textbook).

55 ESTERIFICATIONESTERIFICATIONFree OH groups of carbohydrates react with acids to form Free OH groups of carbohydrates react with acids to form estersesters. This . This reaction an change the physical and chemical propteries of sugar.reaction an change the physical and chemical propteries of sugar.

6.6. GLYCOSIDE FORMATION- GLYCOSIDE FORMATION- Hemiacetals and hemiketals reaction with alcohols to form the Hemiacetals and hemiketals reaction with alcohols to form the corressponding aceta or ketal (p.210 of Text).On the contrary when a corressponding aceta or ketal (p.210 of Text).On the contrary when a cycliccyclic hemiacetal or hemiketal form of monosaccharide reacts with alcohol, the hemiacetal or hemiketal form of monosaccharide reacts with alcohol, the new linkage is called new linkage is called glycosidic linkageglycosidic linkage and the compound and the compound glycoside.glycoside.

Alfa & beta GLYCOCIDIC BONDAlfa & beta GLYCOCIDIC BOND

REDUCING SUGARSREDUCING SUGARS

All monosacchs are reducing sugars.All monosacchs are reducing sugars.They can be oxidised by weak oxidising They can be oxidised by weak oxidising agent such as Benedict’s reagentagent such as Benedict’s reagentBenedict's reagent is a solution of copper Benedict's reagent is a solution of copper sulfate, sodium hydroxide, and tartaric sulfate, sodium hydroxide, and tartaric acid. acid.

Aqueous glucose is mixed with Benedict's reagent and heated. Aqueous glucose is mixed with Benedict's reagent and heated. The reaction reduces the blue copper (II) ion to form a brick red The reaction reduces the blue copper (II) ion to form a brick red precipitate of copper (I) oxide. Because of this, glucose is precipitate of copper (I) oxide. Because of this, glucose is

classified as a reducing sugarclassified as a reducing sugar. .

2.5 IMPORTANT MONOSACCHARIDES

GLUCOSE GLUCOSE FRUCTOSEFRUCTOSEGALACTOSEGALACTOSE

D-Glucose:D-Glucose:D-glucose (dextrose) is the primary fuel in living cells especially in brain cells that have few or no mitochondria.

Cells such as eyeballs have limited oxygen supply and use large amount of glucose to generate energy

Dietary sources include plant starch, and the disaccharides lactose, maltose, and sucrose

DIABETES (diabetes mellitus)DIABETES (diabetes mellitus)Characterized by high blood glucose levels that splills Characterized by high blood glucose levels that splills over into the urineover into the urineThese high glucose levels impairs the insulin-stimulated These high glucose levels impairs the insulin-stimulated glucose entry into cells and starve the cells of insulin. glucose entry into cells and starve the cells of insulin. This leads to This leads to ketosisketosis or high levels of ketone bodies or high levels of ketone bodies (acids) that hinders the buffering capacity of the blood in (acids) that hinders the buffering capacity of the blood in the kidney, which controls blood pH (by excreting excess the kidney, which controls blood pH (by excreting excess H+ ions into the urine).H+ ions into the urine).The H+ excretion is accompanied by the excretion The H+ excretion is accompanied by the excretion ammonia, sodium,potassium, and phosphate ions ammonia, sodium,potassium, and phosphate ions causing severe dehydrationcausing severe dehydrationThis leads to excessive thirst symptom of diabetes and This leads to excessive thirst symptom of diabetes and life-threatening decrease in blood volume.life-threatening decrease in blood volume.

Important monosaccharides. Cont

FRUCTOSE FRUCTOSE – D-fructose (levulose) is often referred as fruit sugar D-fructose (levulose) is often referred as fruit sugar

and is found in some vegetables and honeyand is found in some vegetables and honey– This molecule is an important member of ketose This molecule is an important member of ketose

member of sugarsmember of sugars– It is twice as sweet as sucrose (per gram basis) and is It is twice as sweet as sucrose (per gram basis) and is

used as sweeting agent in processed food productsused as sweeting agent in processed food products– It is present in large amounts in male reproductive It is present in large amounts in male reproductive

tract and is synthesised in the seminal vesicles.tract and is synthesised in the seminal vesicles.

Important monosaccharides. Cont....Important monosaccharides. Cont....

GALACTOSE GALACTOSE – is necessary to synthesize a variety of biomolecules is necessary to synthesize a variety of biomolecules

((lactoselactose-in mammalary glands, -in mammalary glands, glycolipidsglycolipids, certain , certain phospholipidsphospholipids, , proteoglycansproteoglycans, and , and glycoproteinsglycoproteins))

– Galactose and glucose are epimers at carbon 4 and Galactose and glucose are epimers at carbon 4 and interconversion is catalysed by enzyme interconversion is catalysed by enzyme epimeraseepimerase..

– Medical problems – Medical problems – galactosemiagalactosemia (genetic disorder) (genetic disorder) where enzyme to metabolize galactose is missing; where enzyme to metabolize galactose is missing; accumulation of galactoseaccumulation of galactose in the body can cause in the body can cause liver liver damagedamage, , cataractscataracts, and severe , and severe mental retardationmental retardation

2.7.MONOSACCHARIDE DERVATIVES

URONIC ACIDS – formed when terminal URONIC ACIDS – formed when terminal CHCH22OH group of a mono sugar is oxidisedOH group of a mono sugar is oxidised

– Important acids in animals – D-glucuronic acid Important acids in animals – D-glucuronic acid and its epimer L-iduronic acidand its epimer L-iduronic acid

– In liver cells glucuronic acid combines with In liver cells glucuronic acid combines with steroids, certain drugs, and bilirubin to steroids, certain drugs, and bilirubin to improve water solubility therby helping the improve water solubility therby helping the removal of waste products from the bodyremoval of waste products from the body

– These acids are abundant in the connective These acids are abundant in the connective tissue carbohydrate components.tissue carbohydrate components.

Mono sugar derivatives

AMINO SUGARS –AMINO SUGARS –– Sugars in which a hydroxyl group (common Sugars in which a hydroxyl group (common

on carbon 2) is replaced by an amino group on carbon 2) is replaced by an amino group e.g. D-glucosamine and D-galactosaminee.g. D-glucosamine and D-galactosamine

– common constituents of complex common constituents of complex carbohydrate molecule found attached to carbohydrate molecule found attached to cellular proteins and lipidscellular proteins and lipids

– Amino acids are often acetylated e.g. N-Amino acids are often acetylated e.g. N-acetyl-glucosamine.acetyl-glucosamine.

Mono sugar derivatives

DEOXYSUGARS DEOXYSUGARS – monosaccharides in which an - H has replaced an – monosaccharides in which an - H has replaced an –

OH groupOH group– Important sugars: L-fucose (formed from D-mannose Important sugars: L-fucose (formed from D-mannose

by reduction reactions) and 2-deoxy-D-riboseby reduction reactions) and 2-deoxy-D-ribose– L-fucose – found among carbohydrate components of L-fucose – found among carbohydrate components of

glycoproteins, such as those of the ABO blood group glycoproteins, such as those of the ABO blood group determinates on the surface of red blood cellsdeterminates on the surface of red blood cells

– 2-deoxyribose is the pentose sugar component of 2-deoxyribose is the pentose sugar component of DNA.DNA.

GLYCOSIDESGLYCOSIDES• Monosaccharides Monosaccharides can be linked by glycosidic bonds can be linked by glycosidic bonds

(joining of 2 hydroxyl groups of sugars by splitting out (joining of 2 hydroxyl groups of sugars by splitting out water molecule) to create larger structures.water molecule) to create larger structures.

• Disaccharides Disaccharides contain 2 monosaccharides e.g. lactose contain 2 monosaccharides e.g. lactose (galactose+glucose); maltose (glucose+glucose); (galactose+glucose); maltose (glucose+glucose); sucrose (glucose+fructose)sucrose (glucose+fructose)

• OligosaccharidesOligosaccharides – 3 to 12 monosaccharides units – 3 to 12 monosaccharides units e.g. glycoproteinse.g. glycoproteins

• Polysaccharides Polysaccharides – more than 12 monosaccharides – more than 12 monosaccharides units e.g. glycogen (units e.g. glycogen (homopolysaccharidehomopolysaccharide) having ) having hundreds of sugar units; glycosaminoglycans hundreds of sugar units; glycosaminoglycans ((heteropolysaccharidesheteropolysaccharides) containing a number of different ) containing a number of different monosaccharides speciesmonosaccharides species..

Section 3Section 3

DISACCHARIDES DISACCHARIDES

AND AND

OLIGOSACCHARIDESOLIGOSACCHARIDES

DISACCHARIDES AND DISACCHARIDES AND OLIGOSACCHARIDESOLIGOSACCHARIDES

Cnfigurations: Cnfigurations: alfaalfa or or betabeta ( 1,4, glycosidic ( 1,4, glycosidic bonds or linkages; other linkages 1,1; 1,2; bonds or linkages; other linkages 1,1; 1,2; 1,3; 1,6) 1,3; 1,6) Digestion aided by enzymes. Defficiency Digestion aided by enzymes. Defficiency of any one enzyme causes unpleasant of any one enzyme causes unpleasant symptoms (symptoms (fermentationfermentation) in colon ) in colon produces gas [bloating of cramps].produces gas [bloating of cramps].Most common defficiency, an ancestoral Most common defficiency, an ancestoral disorder, disorder, lactose intolerancelactose intolerance caused by caused by reduced synthesis of lactasereduced synthesis of lactase

Important sugars of DisaccharidesImportant sugars of Disaccharides

LACTOSE LACTOSE

(milk sugar) disaccharide found in milk; composed of one (milk sugar) disaccharide found in milk; composed of one molecule of galactose and glucose linked through molecule of galactose and glucose linked through betabeta(1,4) (1,4) glycosidic linkage; because of the hemiacetal group of the glycosidic linkage; because of the hemiacetal group of the glucose component, lactose is a reducing sugar glucose component, lactose is a reducing sugar

Lactose intoleranceLactose intolerance

Lactose (milk sugar) in infants is hydrolyzed by Lactose (milk sugar) in infants is hydrolyzed by intestinal enzyme lactase to its component intestinal enzyme lactase to its component monosacch for absorption into the bloodstream monosacch for absorption into the bloodstream (galactose epimerized to glucose). (galactose epimerized to glucose). Most adult mammals have low levels of beta-Most adult mammals have low levels of beta-galactosidase. Hence, much of the lactose they galactosidase. Hence, much of the lactose they ingest moves to the colon, where bacterial ingest moves to the colon, where bacterial fermentation generates large quantities of CO2, fermentation generates large quantities of CO2, H2 and irritating organic acids.H2 and irritating organic acids.These products cause painful digestive upset These products cause painful digestive upset known as known as lactose intolerancelactose intolerance and is common and is common in the African and Asian decent.in the African and Asian decent.

MALTOSE ( malt sugar)MALTOSE ( malt sugar)An intermediate product of starch hydrolysis; it is a disaccharide with an An intermediate product of starch hydrolysis; it is a disaccharide with an alfaalfa(1,4) (1,4) glycosidic linkage between two D-glucose molecules; in solution the free glycosidic linkage between two D-glucose molecules; in solution the free anomeric carbon undergoes mutarotation resulting in an equilibrium mixture of anomeric carbon undergoes mutarotation resulting in an equilibrium mixture of alfaalfa and and betabeta – maltoses; it does not occur freely in nature – maltoses; it does not occur freely in nature

SUCROSE SUCROSE common table sugar: cane sugar or beet sugar produced common table sugar: cane sugar or beet sugar produced in the leaves and stems of plants; it is a disaccharide in the leaves and stems of plants; it is a disaccharide containing both alfa-glucose and beta-fructose residues containing both alfa-glucose and beta-fructose residues linked by linked by alfa,betaalfa,beta(1,2)glycosidic bond.(1,2)glycosidic bond.

CELLOBIOSE CELLOBIOSE

degradation product of cellulose degradation product of cellulose containing two molecules of glucose linked containing two molecules of glucose linked by a by a betabeta (1,4) glycosidic bond; it does not (1,4) glycosidic bond; it does not occur freely in natureoccur freely in nature

OLIGOSACCHARIDE SUGARSOLIGOSACCHARIDE SUGARS

Oligosaccharides are small polymers often Oligosaccharides are small polymers often found attached to polypeptides in found attached to polypeptides in glycoproteinsglycoproteins and some and some glycolipidsglycolipids. .

They are attached to membrane and They are attached to membrane and secretory proteins found in endoplasmic secretory proteins found in endoplasmic reticulum and Golgi complex of various reticulum and Golgi complex of various cellscells

Two classes: N-linked and O-linkedTwo classes: N-linked and O-linked

Section 4Section 4POLYSACCHARIDESPOLYSACCHARIDES

4.1. Intro to Polysaccharides 4.1. Intro to Polysaccharides 4.2. Classification of Polisacharides4.2. Classification of Polisacharides4.2.1. Homosacharides4.2.1. Homosacharides4.2.2. 4.2.2. HeteropolysacharidesHeteropolysacharides

4.1. Intro to Polysaccharides4.1. Intro to Polysaccharides

Composed of large number of monosaccharide units Composed of large number of monosaccharide units connected by glycosidic linkagesconnected by glycosidic linkagesClassified on the basis of their main monosaccharide Classified on the basis of their main monosaccharide components and the sequences and linkages between components and the sequences and linkages between them, as well as the anomeric configuration of linkages, them, as well as the anomeric configuration of linkages, the ring size (furanose or pyranose), the absolute the ring size (furanose or pyranose), the absolute configuration (D- or L-) and any other substituents configuration (D- or L-) and any other substituents present. present. (http://www.lsbu.ac.uk/water/hypol.html)(http://www.lsbu.ac.uk/water/hypol.html)

Polysaccharides are more hydrophobic if they have a Polysaccharides are more hydrophobic if they have a greater number of internal hydrogen bonds, and as their greater number of internal hydrogen bonds, and as their hydrophobicity increases there is less direct interaction hydrophobicity increases there is less direct interaction with water with water Divided into Divided into homopolysaccharides homopolysaccharides (e.g.Starch, glycogen, (e.g.Starch, glycogen, cellulose, and chitin) & cellulose, and chitin) & heteropolysaccharides heteropolysaccharides (glycoaminoglycans or GAGs, murein).(glycoaminoglycans or GAGs, murein).

4.2. Classification of Polisacharides4.2. Classification of Polisacharides

4.2.1.HOMOSACCHARIDES4.2.1.HOMOSACCHARIDES

Found in abundance in natureFound in abundance in natureImportant examples: starch, glycogen, cellulose, Important examples: starch, glycogen, cellulose, and chitinand chitinStarch, glycogen, and cellulose all yield D-Starch, glycogen, and cellulose all yield D-glucose when they are hydrolyzedglucose when they are hydrolyzedCellulose - primary component of plant cellsCellulose - primary component of plant cellsChitin – principal structural component of Chitin – principal structural component of exoskeletons of arthropods and cell walls of exoskeletons of arthropods and cell walls of many fungi; yield glucose derivative N-acetyl many fungi; yield glucose derivative N-acetyl glucosamine when it is hydrolyzed. glucosamine when it is hydrolyzed.

STARCH (Homosaccharide)STARCH (Homosaccharide)

A naturally abundant nutrient carbohydrate, (CA naturally abundant nutrient carbohydrate, (C66HH1010OO55)n, found )n, found chiefly in the seeds, fruits, tubers, roots, and stem pith of plants, chiefly in the seeds, fruits, tubers, roots, and stem pith of plants, notably in corn, potatoes, wheat, and rice, and varying widely in notably in corn, potatoes, wheat, and rice, and varying widely in appearance according to source but commonly prepared as a white appearance according to source but commonly prepared as a white amorphous tasteless powder. amorphous tasteless powder. Any of various substances, such as natural starch, used to stiffen Any of various substances, such as natural starch, used to stiffen cloth, as in laundering. cloth, as in laundering. Two polysaccharides occur together in starch: amylose and Two polysaccharides occur together in starch: amylose and amylopectinamylopectinAmylose – unbranched chains of D-glucose residues linked with Amylose – unbranched chains of D-glucose residues linked with alfa(alfa(1,4,)glycosidic bonds1,4,)glycosidic bondsAmylopectin – a branched polymer containing both Amylopectin – a branched polymer containing both alfaalfa(1,4,) and (1,4,) and alfa(1,6) glcosidic linkages; the alfa(1,6) glcosidic linkages; the alfa(alfa(1,6) branch points may occur 1,6) branch points may occur every 20-25 glucose residues to prevent helix formationevery 20-25 glucose residues to prevent helix formationStarch digestion begins in the mouth; alfa-amylase in the saliva Starch digestion begins in the mouth; alfa-amylase in the saliva initiates hydrolysis of the gycosidic linkagesinitiates hydrolysis of the gycosidic linkages

GLYCOGEN (Homosaccharide)GLYCOGEN (Homosaccharide)Glycogen is the storage form of glucose in animals and humans Glycogen is the storage form of glucose in animals and humans which is analogous to the starch in plants. which is analogous to the starch in plants. Glycogen is synthesized and stored mainly in the liver and the Glycogen is synthesized and stored mainly in the liver and the muscles. muscles. Structurally, glycogen is very similar to amylopectin with alpha Structurally, glycogen is very similar to amylopectin with alpha acetal linkages, however, it has even more branching and more acetal linkages, however, it has even more branching and more glucose units are present than in amylopectin.glucose units are present than in amylopectin. Various samples of glycogen have been measured at 1,700-Various samples of glycogen have been measured at 1,700-600,000 units of glucose.600,000 units of glucose.The structure of glycogen consists of long polymer chains of The structure of glycogen consists of long polymer chains of glucose units connected by an glucose units connected by an alpha acetalalpha acetal linkage. linkage. The branches are formed by linking C # 1 to a C # 6 through an The branches are formed by linking C # 1 to a C # 6 through an acetal linkages. acetal linkages. In glycogen, the branches occur at intervals of 8-10 glucose units, In glycogen, the branches occur at intervals of 8-10 glucose units, while in amylopectin the branches are separated by 12-20 glucose while in amylopectin the branches are separated by 12-20 glucose units.units.

STRUCTURE OF GLYCOGENSTRUCTURE OF GLYCOGEN

CELLULOSE (Homosaccharide)CELLULOSE (Homosaccharide)

Cellulose is found in plants as microfibrils (2-20 nm diameter and Cellulose is found in plants as microfibrils (2-20 nm diameter and 100 - 40 000 nm long). These form the structurally strong  100 - 40 000 nm long). These form the structurally strong  framework in the cell walls. framework in the cell walls. Cellulose is mostly prepared from wood pulp Cellulose is mostly prepared from wood pulp Cellulose is a linear polymer of β-(1 4)-D-glucopyranose units in Cellulose is a linear polymer of β-(1 4)-D-glucopyranose units in 44CC11 conformation. The fully equatorial conformation of β-linked conformation. The fully equatorial conformation of β-linked glucopyranose residues stabilizes the chair structure, minimizing its glucopyranose residues stabilizes the chair structure, minimizing its flexibilityflexibilityCellulose has many uses as an anticake agent, emulsifier, stabilizer, Cellulose has many uses as an anticake agent, emulsifier, stabilizer, dispersing agent, thickener, and gelling agent but these are dispersing agent, thickener, and gelling agent but these are generally subsidiary to its most important use of holding on to water. generally subsidiary to its most important use of holding on to water. Water cannot penetrate crystalline cellulose but dry amorphous Water cannot penetrate crystalline cellulose but dry amorphous cellulose absorbs water becoming soft and flexible. cellulose absorbs water becoming soft and flexible. Purified cellulose is used as the base material for a number of Purified cellulose is used as the base material for a number of water-soluble derivatives e.g. Methyl cellulose, carbomethycellulosewater-soluble derivatives e.g. Methyl cellulose, carbomethycellulose

Cellulose as polymer of β-D-glucoseCellulose as polymer of β-D-glucose

Cellulose in 3D Cellulose in 3D

CELLULOSECELLULOSE

CHITIN (Homosaccharide)CHITIN (Homosaccharide)

Chitin is a polymer that can be found in anything from Chitin is a polymer that can be found in anything from the shells of beetlesto webs of spiders. It is present all the shells of beetlesto webs of spiders. It is present all around us, in plant and animal creatures. around us, in plant and animal creatures. It is sometimes considered to be a spinoff of It is sometimes considered to be a spinoff of cellulosecellulose, , because the two are very molecularly similar. because the two are very molecularly similar. Cellulose contains a hydroxy group, and chitin contains Cellulose contains a hydroxy group, and chitin contains acetamide. acetamide. Chitin is unusual because it is a "natural polymer," or a Chitin is unusual because it is a "natural polymer," or a combination of elements that exists naturally on earth. combination of elements that exists naturally on earth. Usually, polymers are man-made. Crabs, beetles, worms Usually, polymers are man-made. Crabs, beetles, worms and mushrooms contain large amount of chitin. and mushrooms contain large amount of chitin. Chitin is a very firm material, and it help protect an insect Chitin is a very firm material, and it help protect an insect against harm and pressure against harm and pressure

Structure of the chitin molecule, showing two of the N-Structure of the chitin molecule, showing two of the N-acetylglucosamine units that repeat to form long chains in acetylglucosamine units that repeat to form long chains in

beta-1,4 linkage.beta-1,4 linkage.

CHITOSANCHITOSANA spinoff of chitin that has been discovered by the A spinoff of chitin that has been discovered by the market is chitosan. This is a man-made molecule that is market is chitosan. This is a man-made molecule that is often used to dye shirts and jeans in the clothing often used to dye shirts and jeans in the clothing industry. industry. Chitosan can be used within the human body to regulate Chitosan can be used within the human body to regulate diet programs, and researchers are looking into ways in diet programs, and researchers are looking into ways in which it can sure diseases. which it can sure diseases. Chitin, the polysaccharide polymer from which chitosan Chitin, the polysaccharide polymer from which chitosan is derived, is a cellulose-like polymer consisting mainly of is derived, is a cellulose-like polymer consisting mainly of unbranched chains of N-acetyl-D-glucosamine. unbranched chains of N-acetyl-D-glucosamine. Deacetylated chitin, or chitosan, is comprised of chains Deacetylated chitin, or chitosan, is comprised of chains of D-glucosamine. When ingested, chitosan can be of D-glucosamine. When ingested, chitosan can be considered a dietary fiber. considered a dietary fiber.

CHEMICAL STRUCTURE OF CHITOSANCHEMICAL STRUCTURE OF CHITOSANhttp://www.pdrhealth.com/drug_info/nmdrugprofiles/nutsupdrugs/chi_0067.shtmlhttp://www.pdrhealth.com/drug_info/nmdrugprofiles/nutsupdrugs/chi_0067.shtml

4.2.2.HETEROPOLYSACCHARIDES4.2.2.HETEROPOLYSACCHARIDES

Are high-molecular-weight carbohydrate Are high-molecular-weight carbohydrate polymers more than one kind of polymers more than one kind of monosaccharidemonosaccharide

Important examples include Important examples include glycosaminoglycans (GAGs) – the glycosaminoglycans (GAGs) – the principle components of proteoglycans principle components of proteoglycans and murein, a major component of and murein, a major component of bacterial cell walls. bacterial cell walls.

GAGs - high-molecular-weight GAGs - high-molecular-weight carbohydrate polymerscarbohydrate polymers

GlycosaminoglycansGlycosaminoglycans forming the forming the proteoglycans are the most abundant proteoglycans are the most abundant heteropolysaccharidesheteropolysaccharides in the body. They are in the body. They are long unbranched molecules containing a long unbranched molecules containing a repeating disaccharide unitrepeating disaccharide unit. Usually one sugar is . Usually one sugar is an uronic acid (eitheran uronic acid (either D-glucuronic D-glucuronic or or L-iduronicL-iduronic) ) and the other is either and the other is either GlcNAcGlcNAc or or GalNAcGalNAc. One . One or both sugars contain sulfate groups (the only or both sugars contain sulfate groups (the only exception is hyaluronic acid). exception is hyaluronic acid).

GAGs are highly negatively charged what is GAGs are highly negatively charged what is essential for their function.essential for their function.

THE SPECIFIC GAGs OF PHYSIOLOGICAL THE SPECIFIC GAGs OF PHYSIOLOGICAL SIGNIFICANCE SIGNIFICANCE

Hyaluronic acidHyaluronic acid OccurenceOccurence : synovial fluid, ECM of loose : synovial fluid, ECM of loose connective tissueconnective tissueHyaluronic acidHyaluronic acid is unique among the GAGs is unique among the GAGs because it does not contain any sulfate and is because it does not contain any sulfate and is not found covalently attached to proteins. It not found covalently attached to proteins. It forms non-covalently linked complexesforms non-covalently linked complexes with with proteoglycansproteoglycans in the ECM. in the ECM.Hyaluronic acid polymers are very large (100 - Hyaluronic acid polymers are very large (100 - 10,000 kD) and can displace a large volume of 10,000 kD) and can displace a large volume of water. water.

Hyaluronic acidHyaluronic acid (D-glucuronate + GlcNAc) (D-glucuronate + GlcNAc)

Dermatan sulfateDermatan sulfate (L-iduronate + GlcNAc sulfate) (L-iduronate + GlcNAc sulfate)

OccurenceOccurence : skin, blood vessels, heart valves : skin, blood vessels, heart valves

Chondroitin sulfate Chondroitin sulfate (D-glucuronate + (D-glucuronate + GalNAc sulfate)GalNAc sulfate)

OccurenceOccurence : cartilage, bone, heart valves ; : cartilage, bone, heart valves ;It is the most abundant GAG.It is the most abundant GAG.

Heparin and heparan sulfate Heparin and heparan sulfate (D-glucuronate (D-glucuronate sulfate + N-sulfo-D-glucosamine)sulfate + N-sulfo-D-glucosamine)

Heparans have less sulfate groups than heparins Heparans have less sulfate groups than heparins OccurenceOccurence : : Heparin Heparin :component of intracellular granules of mast cells lining the :component of intracellular granules of mast cells lining the arteries of the lungs, liver and skin arteries of the lungs, liver and skin Heparan sulfateHeparan sulfate : basement : basement membranes, component of cell surfacesmembranes, component of cell surfaces

Keratan sulfate Keratan sulfate ( Gal + GlcNAc sulfate)( Gal + GlcNAc sulfate)

OccurenceOccurence : cornea, bone, cartilage ; : cornea, bone, cartilage ;

Keratan sulfates are often aggregated with chondroitin Keratan sulfates are often aggregated with chondroitin sulfatessulfates..

MUREIN (Peptidoglycan)MUREIN (Peptidoglycan)

PeptidoglycanPeptidoglycan, also known as , also known as mureinmurein, is a polymer consisting of , is a polymer consisting of sugars and amino acids that forms a mesh-like layer outside the sugars and amino acids that forms a mesh-like layer outside the plasma membrane of eubacteria. plasma membrane of eubacteria.

The sugar component consists of alternating residues of β-(1,4) The sugar component consists of alternating residues of β-(1,4) linked N-acetylglucosamine and N-acetylmuramic acid residues. linked N-acetylglucosamine and N-acetylmuramic acid residues.

Attached to the N-acetylmuramic acid is a peptide chain of three to Attached to the N-acetylmuramic acid is a peptide chain of three to five amino acids. five amino acids.

The peptide chain can be cross-linked to the peptide chain of The peptide chain can be cross-linked to the peptide chain of another strand forming the 3D mesh-like layer. another strand forming the 3D mesh-like layer.

Some Archaea have a similar layer of pseudopeptidoglycan. Some Archaea have a similar layer of pseudopeptidoglycan.

Peptidoglycan serves a structural role in the bacterial cell Peptidoglycan serves a structural role in the bacterial cell wall, giving the wall shape and structural strength, as wall, giving the wall shape and structural strength, as well as counteracting the osmotic pressure of the well as counteracting the osmotic pressure of the cytoplasm. cytoplasm.

Peptidoglycan is also involved in binary fission during Peptidoglycan is also involved in binary fission during bacterial cell reproduction.bacterial cell reproduction.

The peptidoglycan layer is substantially thicker in Gram-The peptidoglycan layer is substantially thicker in Gram-positive bacteria (20 to 80 nm) than in Gram-negative positive bacteria (20 to 80 nm) than in Gram-negative bacteria (7 to 8 nm), with the attachment of the S-layer. bacteria (7 to 8 nm), with the attachment of the S-layer.

Peptidoglycan forms around 90% of the dry weight of Peptidoglycan forms around 90% of the dry weight of Gram-positive bacteria but only 10% of Gram-negative Gram-positive bacteria but only 10% of Gram-negative strains. strains.

In Gram-positive strains, it is important in attachment In Gram-positive strains, it is important in attachment roles and serotyping purposes.roles and serotyping purposes.

SECTION 5SECTION 5

GLYCOCONJUGATESGLYCOCONJUGATES5.1. 5.1. Intro to glycoconjugates Intro to glycoconjugates 5.2. 5.2. glycoproteinsglycoproteins5.3.5.3. glycosylationglycosylation5.4.5.4. proteoglycansproteoglycans

5.1. Intro to glycoconjugates5.1. Intro to glycoconjugates

They are compounds that result from covalent They are compounds that result from covalent linkages of carbohydrate molecules to both linkages of carbohydrate molecules to both proteins and lipids.proteins and lipids.They have a profound effects on the functions of They have a profound effects on the functions of individual cells as weell as cell-cell interactions individual cells as weell as cell-cell interactions of multicellular organisms.of multicellular organisms.Two classes of carbohydrate-protein conjugate: Two classes of carbohydrate-protein conjugate: glycoproteinsglycoproteins and and proteoglycans.proteoglycans.The The glycolipidsglycolipids (oligosaccharide-containing lipid (oligosaccharide-containing lipid molecules) are found predominately on the outer molecules) are found predominately on the outer surface of plasma membrane.surface of plasma membrane.

5.2.glycoproteins5.2.glycoproteinsGlycoprotein carbohydrate chains are highly diverse. Glycoprotein carbohydrate chains are highly diverse. They are formed by They are formed by glycosylationglycosylation and classified into and classified into two groups: two groups: 1. N-linked oligosaccharides1. N-linked oligosaccharides2. O-linked oligosaccharides2. O-linked oligosaccharidesThe N-linked oligosaccharides have a minimum of 5 The N-linked oligosaccharides have a minimum of 5 sugar residuessugar residuesN-linked attached to polypeptides by an N-linked attached to polypeptides by an N-glycosidic N-glycosidic bondbond with a chain amide group of amino acid and with a chain amide group of amino acid and asparagineasparagineO-linked oligosaccharides are generally short (1-4 sugar O-linked oligosaccharides are generally short (1-4 sugar residues) residues) O-linked are O-linked are attached to polypeptides by the side chain attached to polypeptides by the side chain hydroxyl group of amino acidshydroxyl group of amino acids serine or threonine in serine or threonine in polypeptide chains or hydroxyl groups of membrane polypeptide chains or hydroxyl groups of membrane lipidslipids

5.3.glycosylation5.3.glycosylationGlycosylation is the process or result of addition of Glycosylation is the process or result of addition of saccharides to proteins and lipidssaccharides to proteins and lipidsThe process plays an important role in the synthesis of The process plays an important role in the synthesis of membrane and secreted proteinsmembrane and secreted proteinsMajority of proteins synthesized in the rough ER undergo Majority of proteins synthesized in the rough ER undergo glycosylationglycosylationIt is an enzyme -directed site-specific process.It is an enzyme -directed site-specific process.Two types of glycosylation exist: Two types of glycosylation exist: NN-linked -linked glycosylation glycosylation to the to the amide nitrogenamide nitrogen of asparagine side chains and of asparagine side chains and OO--linked linked glycosylation to the glycosylation to the hydroxy oxygenhydroxy oxygen of of serineserine and and threoninethreonine side chains. side chains.Glycosylation may play a role in cell-cell adhesion (a Glycosylation may play a role in cell-cell adhesion (a mechanism employed by cells of the mechanism employed by cells of the immune systemimmune system), ), as well. as well.

GLYCOPROTEIN FUNCTIONSGLYCOPROTEIN FUNCTIONSTypes of glycoproteins: asparagine-linked carbohydrate; Types of glycoproteins: asparagine-linked carbohydrate; mucin-type cabohydratemucin-type cabohydrateExamples: Examples: glycophoringlycophorin (membrane protein, source – (membrane protein, source – human RBC, % carbohydrate - 60); human RBC, % carbohydrate - 60); potato lectinpotato lectin (lectin, (lectin, carbohydrate binding proteins, source – potato, % carbohydrate binding proteins, source – potato, % carbohydrate – 50)carbohydrate – 50)FunctionsFunctions: Many glycoproteins have : Many glycoproteins have structuralstructural functions: constituent of the functions: constituent of the cell wallcell wall; form ; form connective connective tissuestissues such as collagen; found in gastrointestinal such as collagen; found in gastrointestinal mucus mucus secretions;secretions; used as used as protectiveprotective agents and agents and lubricants ;found abundantly in the lubricants ;found abundantly in the blood plasmablood plasma. . The human blood groups A, B, AB, and O depend on the The human blood groups A, B, AB, and O depend on the oligosaccharide part of the glycoprotein on the surface oligosaccharide part of the glycoprotein on the surface of erythrocyte cells. The terminal monosaccharide of the of erythrocyte cells. The terminal monosaccharide of the glycoprotein at the nonreducing end determines blood glycoprotein at the nonreducing end determines blood group.group.

BLOOD GROUPSBLOOD GROUPSTYPETYPE TERMINAL SUGARTERMINAL SUGARAA N-acetylgalactosamineN-acetylgalactosamineBB -D-galactose-D-galactoseABAB both the aboveboth the aboveOO neither of the aboveneither of the aboveO O is the “universal is the “universal donor”donor”AB AB is the “universal is the “universal

acceptor”acceptor”

Oligosaccharides are antigeneic Oligosaccharides are antigeneic determinantsdeterminants

Carbohydrates on cell surfaces are Carbohydrates on cell surfaces are immunochemical markers.immunochemical markers.ABO blood group antigensABO blood group antigens are oligosaccharide are oligosaccharide components of glycoproteins and glycolipids on components of glycoproteins and glycolipids on the surfaces of individual cells, besides blood the surfaces of individual cells, besides blood cells.cells. Individuals with type A cells have A antigens on Individuals with type A cells have A antigens on their cell surfaces and carry anti-B antibodiestheir cell surfaces and carry anti-B antibodiesThose with type B cells which bear B antigens, Those with type B cells which bear B antigens, carry anti-A antibodies carry anti-A antibodies

Those with type AB cells, which have both A and Those with type AB cells, which have both A and B antigens, carry neither anti-A nor anti-B B antigens, carry neither anti-A nor anti-B antibodiesantibodies

Type O individuals whose cells bear neither Type O individuals whose cells bear neither antigen, carry both anti-A and anti-B antibodies.antigen, carry both anti-A and anti-B antibodies.

Transfusion of type A blood group into a type B Transfusion of type A blood group into a type B individual, results in an anti-A antibody- A individual, results in an anti-A antibody- A antigen reaction. antigen reaction.

This reaction clumps together (agglutinates) the This reaction clumps together (agglutinates) the transfused erythrocytes, resulting in an often transfused erythrocytes, resulting in an often fatal blockage of blood vesselsfatal blockage of blood vessels

Functions of glycoproteins (elaborated)Functions of glycoproteins (elaborated)http://www.cs.stedwards.edu/chem/Chemistry/CHEM43/CHEM43/Glycoproteins/Glycoproteins.HTMLhttp://www.cs.stedwards.edu/chem/Chemistry/CHEM43/CHEM43/Glycoproteins/Glycoproteins.HTML

Carbohydrates and proteins by themselves serve in a vast Carbohydrates and proteins by themselves serve in a vast number of biological functions,linking the two together number of biological functions,linking the two together results in a macromolecule with an extremely large results in a macromolecule with an extremely large number of functions.number of functions.StructuralStructural: Glycoproteins are found throughout : Glycoproteins are found throughout matrices. They act as receptors on cell surfaces that matrices. They act as receptors on cell surfaces that bring other cells and proteins (collagen) together giving bring other cells and proteins (collagen) together giving strength and support to a matrix.strength and support to a matrix. In nerve tissue glycoproteins are abundant in gray In nerve tissue glycoproteins are abundant in gray matter and appear to be associated with synaptosomes, matter and appear to be associated with synaptosomes, axons, and microsomes.axons, and microsomes.ProtectionProtection: Human lacrimal glands produce a : Human lacrimal glands produce a glycoprotein which protects the corneal epithelium from glycoprotein which protects the corneal epithelium from desiccation and foreign particles. Human sweat glands desiccation and foreign particles. Human sweat glands secrete glycoproteins which protect the skin from the secrete glycoproteins which protect the skin from the other excretory products that could harm the skin other excretory products that could harm the skin

Functions of glycoproteins (further elaborated-1)Functions of glycoproteins (further elaborated-1)

Prothrombin, thrombin, and fibrinogen are all Prothrombin, thrombin, and fibrinogen are all glycoproteins that play an intricate role in the blood glycoproteins that play an intricate role in the blood clotting mechanismclotting mechanismIn certain bacteria the slime layer that surrounds the In certain bacteria the slime layer that surrounds the outermost components of cell walls are made up of outermost components of cell walls are made up of glycoproteins of high molecular weight. In addition to glycoproteins of high molecular weight. In addition to forming these s-layers, glycoproteins also function as forming these s-layers, glycoproteins also function as bacterial flagella. These are made up of bundles of bacterial flagella. These are made up of bundles of glycoproteins protruding from the cell's surface. Their glycoproteins protruding from the cell's surface. Their rotation provides propulsion. rotation provides propulsion. In plants, glycoproteins have roles in cell wall formation, In plants, glycoproteins have roles in cell wall formation, tissue differentiation, & embryogenesis.tissue differentiation, & embryogenesis.Reproduction:Reproduction: Glycoproteins found on the surface of Glycoproteins found on the surface of spermatozoa appear to increase a sperm cell's attraction spermatozoa appear to increase a sperm cell's attraction for the egg by altering the electrophoretic mobility of the for the egg by altering the electrophoretic mobility of the plasma membrane. plasma membrane.

Functions of glycoproteins (further elaborated-2)Functions of glycoproteins (further elaborated-2)

AdhesionAdhesion: Glycoproteins serve to adhere cells : Glycoproteins serve to adhere cells to cells and cells to substratum. to cells and cells to substratum. HormonesHormones: There are many glycoproteins that : There are many glycoproteins that function as hormones such as human chorionic function as hormones such as human chorionic gonadotropin (HCG) which is present in human gonadotropin (HCG) which is present in human pregnancy urine. Another example is pregnancy urine. Another example is erythropoietin which regulates erythrocyte erythropoietin which regulates erythrocyte production production Enzymes: Glycoprotein enzymes are of three Enzymes: Glycoprotein enzymes are of three types. These are oxidoreductases, transferases, types. These are oxidoreductases, transferases, and hydrolases.and hydrolases.

Functions of glycoproteins (further elaborated-3)Functions of glycoproteins (further elaborated-3)

CarriersCarriers: Glycoproteins can bind to certain molecules : Glycoproteins can bind to certain molecules and serve as vehicles of transport. They can bind to and serve as vehicles of transport. They can bind to vitamins, hormones, cations, and other substances. vitamins, hormones, cations, and other substances. InhibitorsInhibitors: Many glycoproteins in blood plasma have : Many glycoproteins in blood plasma have shown antiproteolytic activity. For example, the shown antiproteolytic activity. For example, the glycoprotein a1-antichymotrypsin inhibits chymotrypsin. glycoprotein a1-antichymotrypsin inhibits chymotrypsin. ImmunologicalImmunological: The interaction of blood group : The interaction of blood group substances with antibodies is determined by the substances with antibodies is determined by the glycoproteins on erythrocytes. Many immunoglobulins glycoproteins on erythrocytes. Many immunoglobulins are actually glycoproteins. are actually glycoproteins. B and T cells contain surface glycoproteins that attract B and T cells contain surface glycoproteins that attract bacteria to these sites and bind them. In much the same bacteria to these sites and bind them. In much the same manner, glycoproteins can direct phagocytosis. Because manner, glycoproteins can direct phagocytosis. Because the HIV virus recognizes the receptor protein CD4, it the HIV virus recognizes the receptor protein CD4, it binds to helper T cells which contain it. binds to helper T cells which contain it.

CELL MEMBRANECELL MEMBRANEThe cell membrane is a fluid mosaic of lipids, proteins, The cell membrane is a fluid mosaic of lipids, proteins, and carbohydrates. and carbohydrates. Membrane carbohydrates are usually branched Membrane carbohydrates are usually branched oligosaccharides with fewer than 15 sugar units. oligosaccharides with fewer than 15 sugar units. Some of these oligosaccharides are covalently bonded Some of these oligosaccharides are covalently bonded to lipids, forming molecules called to lipids, forming molecules called glycolipids.glycolipids. Most are covalently bonded to proteins, which are Most are covalently bonded to proteins, which are thereby thereby glycoproteinsglycoproteins. . Plants produce Plants produce pectinpectin, major component of cell wall., major component of cell wall.The oligosaccharides on the external side of the plasma The oligosaccharides on the external side of the plasma membrane vary from species to species membrane vary from species to species The diversity of the molecules and their location on the The diversity of the molecules and their location on the cell's surface enable oligosaccharides to function as cell's surface enable oligosaccharides to function as markers that distinguish one cell from another.markers that distinguish one cell from another.

THE MOSAIC OF CELL’S MEMBRANETHE MOSAIC OF CELL’S MEMBRANE

CELL MEMBRANE MATRIXCELL MEMBRANE MATRIXThe biological membrane is a collage of many The biological membrane is a collage of many different different proteinsproteins embedded in the fluid matrix embedded in the fluid matrix of the of the lipid bilayerlipid bilayer. .

The The lipid bilayerlipid bilayer is the main fabric of the is the main fabric of the membrane, and its structure creates a semi-membrane, and its structure creates a semi-permeable membrane. permeable membrane.

The hydrophobic core impedes the transport of The hydrophobic core impedes the transport of hydrophilic structures, such as ions and polar hydrophilic structures, such as ions and polar molecules but enable hydrophobic molecules, molecules but enable hydrophobic molecules, which can dissolve in the membrane, cross it which can dissolve in the membrane, cross it with ease. with ease.

Protein layer of cell membraneProtein layer of cell membraneProteins determine most of the Proteins determine most of the membrane's specific functions. membrane's specific functions.

The plasma membrane and the The plasma membrane and the membranes of the various organelles each membranes of the various organelles each have unique collections of proteins. have unique collections of proteins.

For example, to date more than 50 kinds For example, to date more than 50 kinds of proteins have been found in the plasma of proteins have been found in the plasma membrane of red blood cells.membrane of red blood cells.

5.4. PROTEOGLYCANS5.4. PROTEOGLYCANS

ProteoglycansProteoglycans represent a special class of represent a special class of glycoproteins that are heavily glycosylated. glycoproteins that are heavily glycosylated. They consist of a core protein with one or more They consist of a core protein with one or more covalently attached glycosaminoglycan chain(s). covalently attached glycosaminoglycan chain(s). These These glycosaminoglycan (GAG) chainsglycosaminoglycan (GAG) chains are long, linear are long, linear carbohydrate polymers that are negatively charged carbohydrate polymers that are negatively charged under physiological conditions, due to the occurrence of under physiological conditions, due to the occurrence of sulphate and uronic acid groups.sulphate and uronic acid groups.Proteoglycans can be categorised depending upon the Proteoglycans can be categorised depending upon the nature of their glycosaminoglycan chains. These chains nature of their glycosaminoglycan chains. These chains may be:may be:1. chondroitin sulfate and dematan sulfate 1. chondroitin sulfate and dematan sulfate 2. heparin and heparin sulfate 2. heparin and heparin sulfate 3. keratan sulfate3. keratan sulfate

Proteoglycans can also be categorised by Proteoglycans can also be categorised by size. size.

Example of Example of largelarge proteoglycan is proteoglycan is aggrecan. aggrecan.

AggrecanAggrecan, is the major proteoglycan in , is the major proteoglycan in cartilage, present in many adult tissues cartilage, present in many adult tissues including blood vessels and skin. including blood vessels and skin.

The The smallsmall leucine rich repeat leucine rich repeat proteoglycans (SLRPs) include proteoglycans (SLRPs) include decorin, decorin, biglycan, fibromodulin biglycan, fibromodulin and and lumicanlumican. .

SYNTHESIS OF PROTEOGLYCANSSYNTHESIS OF PROTEOGLYCANS

The protein component of proteoglycans is The protein component of proteoglycans is synthesized by ribosomes and translocated into synthesized by ribosomes and translocated into the lumen of the rough endoplasmic reticulum. the lumen of the rough endoplasmic reticulum. Glycosylation of the proteoglycan occurs in the Glycosylation of the proteoglycan occurs in the Golgi apparatus in multiple enzymatic steps. Golgi apparatus in multiple enzymatic steps. First a special link tetrasaccharide is attached to First a special link tetrasaccharide is attached to a serine side chain on the core protein to serve a serine side chain on the core protein to serve as a primer for polysaccharide growth. as a primer for polysaccharide growth. Then sugars are added one at the time by Then sugars are added one at the time by glycosyl transferase. glycosyl transferase. The completed proteoglycan is then exported in The completed proteoglycan is then exported in secretory vesicles to the extracellular matrix of secretory vesicles to the extracellular matrix of the cell.the cell.

Structure of proteoglycansStructure of proteoglycans The GAGs extend perpendicular from the core protein in a The GAGs extend perpendicular from the core protein in a bottlebrush- like structure. bottlebrush- like structure. The linkage of GAGs such as (The linkage of GAGs such as (heparan sulfates and chondroitin heparan sulfates and chondroitin sulfatessulfates) to the protein core involves a specific trisaccharide linker) to the protein core involves a specific trisaccharide linkerSome forms of Some forms of keratan sulfateskeratan sulfates are linked to the protein core are linked to the protein core through an through an N-asparaginylN-asparaginyl bondbond. . The protein cores of proteoglycans are rich in Ser and Thr residues The protein cores of proteoglycans are rich in Ser and Thr residues which allows multiple GAG attachment. which allows multiple GAG attachment.

FUNCTION OF PROTEOGLYCANSFUNCTION OF PROTEOGLYCANS

Proteoglycans are a major component of the animal Proteoglycans are a major component of the animal extracellular matrixextracellular matrix, the 'filler' substance existing , the 'filler' substance existing between between cellscells in an organism. in an organism. Individual functions of proteoglycans can be attributed to Individual functions of proteoglycans can be attributed to either the protein core or the attached GAG chain.either the protein core or the attached GAG chain.In extracellular matrix, they form large complexes, with In extracellular matrix, they form large complexes, with other proteoglycans, to hyaluronan and to fibrous matrix other proteoglycans, to hyaluronan and to fibrous matrix proteins (such as collagen). proteins (such as collagen). They are also involved in binding cations (such as They are also involved in binding cations (such as sodium, potassium and calcium) and water, and also sodium, potassium and calcium) and water, and also regulating the movement of molecules through the regulating the movement of molecules through the matrix. matrix. They can affect the activity and stability of proteins and They can affect the activity and stability of proteins and signalling molecules within the matrix. signalling molecules within the matrix.

ROLE OF PROTEOGLYCANSROLE OF PROTEOGLYCANShttp://www.cryst.bbk.ac.uk/pps97/assignments/projects/emilia/Proteoglycans.HTMhttp://www.cryst.bbk.ac.uk/pps97/assignments/projects/emilia/Proteoglycans.HTM

GAGGAG dependent functions can be divided into two dependent functions can be divided into two classes: the biophysical and the biochemical. classes: the biophysical and the biochemical.

The The biophysical functionsbiophysical functions depend on the unique depend on the unique properties of GAGs : the ability to fill the space, bind and properties of GAGs : the ability to fill the space, bind and organize water molecules and repel negatively charged organize water molecules and repel negatively charged molecules. Because of high viscosity and low molecules. Because of high viscosity and low compressibility they are ideal for a lubricating fluid in the compressibility they are ideal for a lubricating fluid in the joints. On the other hand their rigidity provides structural joints. On the other hand their rigidity provides structural integrity to the cells and allows the cell migration due to integrity to the cells and allows the cell migration due to providing the passageways between cells. providing the passageways between cells.

For example the large quantities of For example the large quantities of chondroitin sulfate chondroitin sulfate and keratan sulfateand keratan sulfate found on found on aggrecanaggrecan play an play an important role in the important role in the hydration of cartilagehydration of cartilage. They give . They give the cartilage its gel-like properties and resistance to the cartilage its gel-like properties and resistance to deformation. deformation.

Role of proteoglycans contd.Role of proteoglycans contd.The other, more biochemical functions of GAGs The other, more biochemical functions of GAGs are mediated by specific binding of GAGs to are mediated by specific binding of GAGs to other macromolecules, mostly proteins. other macromolecules, mostly proteins. Proteoglycans participate in cell and tissue Proteoglycans participate in cell and tissue development and physiology.development and physiology.

Hurler’s syndrome: (refer Text) disease related Hurler’s syndrome: (refer Text) disease related with proteoglycan metabolism where excessive with proteoglycan metabolism where excessive accumulation of dermatin sulfate due to accumulation of dermatin sulfate due to deficiency of a specific enzyme may cause deficiency of a specific enzyme may cause mental retardation, skeletal deformity ansd death mental retardation, skeletal deformity ansd death in early childhood.in early childhood.

SUMMARYSUMMARYMonosaccharides, the simplest carbohydrates, are Monosaccharides, the simplest carbohydrates, are classified as aldoses or ketoses.classified as aldoses or ketoses.The cyclic hemiacetal and hemiketal forms of The cyclic hemiacetal and hemiketal forms of monosacchs have either alfa or beta configuration at monosacchs have either alfa or beta configuration at their anomeric carbon.their anomeric carbon.Monosacch derivatives include aldonic acids, uronic Monosacch derivatives include aldonic acids, uronic acids, deoxy sugars, amino sugars, alfa & beta acids, deoxy sugars, amino sugars, alfa & beta glycosides.glycosides.Disaccharides simplest polysaccharides occuring as Disaccharides simplest polysaccharides occuring as hydrolysis products of larger molecules e.g. hydrolysis products of larger molecules e.g. Lactose,sucroseLactose,sucroseOligosaccharides play important roles in determining Oligosaccharides play important roles in determining protein structure and in cell-surface recognition protein structure and in cell-surface recognition phenomena. Oligosacchs with 3 or more sugar residues phenomena. Oligosacchs with 3 or more sugar residues are mostly found in plants.are mostly found in plants.

Summary contd. -1Summary contd. -1POLOYSACCHARIDES consist of monosacchs POLOYSACCHARIDES consist of monosacchs linked by glycosidic bonds.linked by glycosidic bonds.Cellulose and chitin are Cellulose and chitin are structural polysacchsstructural polysacchs with beta(1-4) linkages that adopt rigid and with beta(1-4) linkages that adopt rigid and extended structures.extended structures.The The storage polysacchsstorage polysacchs starch and glycogen starch and glycogen consist of alfa-glycosidically linked glucose consist of alfa-glycosidically linked glucose residuesresiduesGlycosaminoglycans Glycosaminoglycans are unbranched are unbranched polysacchs containing uronic acids and amino polysacchs containing uronic acids and amino sugars that are often sulfatedsugars that are often sulfated

Summary contd.-2Summary contd.-2GLYCOCONJUGATESGLYCOCONJUGATES:: Proteoglycans & Proteoglycans & glycoproteins play important roles in information glycoproteins play important roles in information transfer in living organisms.transfer in living organisms.

ProteoglycansProteoglycans are enormous molecules are enormous molecules consisting of hyaluronate with attached core consisting of hyaluronate with attached core proteins that bear numerous proteins that bear numerous glycosaminoglycans and oligosaccharides. glycosaminoglycans and oligosaccharides. Found in the extracellular matrix of tissuesFound in the extracellular matrix of tissues

Bacterial cell walls are made up of Bacterial cell walls are made up of peptidoglycanpeptidoglycan, a network of polysaccharide , a network of polysaccharide and poypeptide chains.and poypeptide chains.

Summary contd.-3Summary contd.-3

GlycoproteinsGlycoproteins or Glycosylated proteins may or Glycosylated proteins may contain N-linked oligosacchs attached to Asn contain N-linked oligosacchs attached to Asn (asparagine) or O-linked oligosacchs attached to (asparagine) or O-linked oligosacchs attached to Ser or Thr (serine or threonine) or bothSer or Thr (serine or threonine) or both

Different molecules of glycoproteins may contain Different molecules of glycoproteins may contain different sequences and locations of different sequences and locations of oligosaccharides.oligosaccharides.

Occur in cells in both soluble and membrane Occur in cells in both soluble and membrane bound forms, and in extracellular fluidsbound forms, and in extracellular fluids

END NOTESEND NOTES

The destiny of a nation depends on the The destiny of a nation depends on the manner in which it feeds itself. manner in which it feeds itself.

We eat to live, NOT, live to eat.We eat to live, NOT, live to eat.

Lower your carbohydrate consumption, but Lower your carbohydrate consumption, but balance it with the right amount of protein balance it with the right amount of protein and fat.and fat.