Lecture 3 - Carbohydrates

8/6/2019 Lecture 3 - Carbohydrates

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LECTURE 3LECTURE 3 --CARBOHYDRATESCARBOHYDRATESCO 2:CO 2:

Describe, Discuss, andDescribe, Discuss, andcompare the classification,compare the classification,

structure and function of structure and function of

carbohydrates and itscarbohydrates and its

derivatives.derivatives.



LECTURE 3LECTURE 3 --CARBOHYDRATESCARBOHYDRATES

TOPICS:TOPICS:

1.1. Role & Significance of Role & Significance of

CarbohydratesCarbohydrates2.2. 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

organismsorganisms (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 . SI NI I N SSect . SI NI I N S

Carbohydrates ar e the most abundantCarbohydrates ar e the most abundantbiomolecules in natur e, having a dir ect linkbiomolecules in natur e, having a dir ect link

between solar energy and the chemical bondbetween solar energy and the chemical bond

energy in living organisms.energy in living organisms.

Sour ce of rapid energy productionSour ce of rapid energy production

Structural building blocks of cellsStructural building blocks of cells

Components of several metabolic pathwaysComponents of several metabolic pathways

ecognition of cellular phenomena, such as cellecognition of cellular phenomena, such as cellr ecognition and binding (e.g., by other cells,r ecognition and binding (e.g., by other cells,

hormones, and viruses)hormones, and viruses)



Carbohydrate : compounds contains H, C & O with theCarbohydrate : 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 thatcompound that contains alcohol & carbonylcontains alcohol & carbonyl

functional groupfunctional group

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

Adehyde Adehyde aldosealdoseKetoneKetone ketoseketose

CARBOHYDRATESCARBOHYDRATES



Examples:Examples:



cellulose, chitin,cellulose, chitin,

starch, glycogen,starch, glycogen,

glucoaminoglycansglucoaminoglycans

disaccharidesdisaccharides

GlycoproteinsGlycoproteins

(bacterial cell(bacterial cell

wallswalls

ClassificationClassification

Carbohydrate

MonoMono

saccharidesaccharide

OligoOligo

saccharidesaccharide

PolyPoly

saccharidesaccharideGlyconoconjugatesGlyconoconjugates

Glucose, fructose

Ribose (aldopentose)

Deoxy ribose

glycoproteins

and

proteoglycans



Sect2.Sect2.

MO OSACHARIDESMO OSACHARIDES



Sect. 2. MonosacharidesSect. 2. Monosacharides

Sub sections :Sub sections :

2.1 Properties & classification2.1 Properties & classification

2.2 Stereoisomers2.2 Stereoisomers2.3 Cyclic structure2.3 Cyclic structure

2.4 Important Reactions2.4 Important Reactions

2.5 Important monosach2.5 Important monosach

2.62.6 glycoproteinsglycoproteins andand proteoglycansproteoglycans

2.72.7 Monosaccharide derivatives



2.1 Monosach Properties& classification2.1 Monosach Properties& classification

Colorless, crystalline solidsSSoluble in water but insoluble in nonpolar solvents

One 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 (Carbohydrates with an aldehyde (--CHO) functionalCHO) functional

group are calledgroup are called aldosesaldoses e.g. glyceraldehyde (CHe.g. glyceraldehyde (CH22OHOH--CHOHCHOH--CHO CHO ))

Those with a keto group (Those with a keto group (--C=O) areC=O) are ketosesketosese.g.dihydroxyacetone (CH2OHe.g.dihydroxyacetone (CH2OH--C=O C=O --CH2OH)CH2OH)

± ± Classified according to the number of carbon atomsClassified according to the number of carbon atomsthey containthey contain



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

Aldotetrose Aldotriose Aldopentoses

Ketotriose Ketotetrose Ketopentose Ketohexose

Aldohexose



2.2. MO OSACCHARIDES STEREOISOMERS2.2. MO OSACCHARIDES STEREOISOMERS

Isomers: same chemical formulas, different structures

Conformation : the spatial arrangement of substituent groupschiral centers: asymmetric carbons, i.e carbon atom with four different substituents

Enantiomers : 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 isthe 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.



DD-- and Land L-- enantiomersenantiomers



2.3 Cyclic structure of monosacharides2.3 Cyclic structure of monosacharides

in aqueous solution, monosaccharides with five or more carbon atoms in the

backbone occur predominantly as cyclic (ring) structures in which the carbonyl grouphas 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. . An English chemist W. .

Haworth gave a more accurateHaworth gave a more accuratepicture of carbohydratepicture of carbohydrate

structure. (Ref. P.205 of structure. (Ref. P.205 of

textbook)textbook)

HAWORTH STRUCTURESHAWORTH STRUCTURES



FISHER A D HAWORTH FORMS OF SUGARFISHER A D HAWORTH FORMS OF SUGAR



SUMMARY OF SUGAR STRUCTURESSUMMARY OF SUGAR STRUCTURES

ISOMERSISOMERS-- compounds that have the same chemical formula e.g.compounds that have the same chemical formula e.g.fructose, glucose, mannose, and galactose are isomers of eachfructose, glucose, mannose, and galactose are isomers of eachother having formula Cother having formula C66HH1212OO66..

EPIMERSEPIMERS-- refer to sugars whose configuration differ around onerefer to sugars whose configuration differ around onespecific carbon atom e.g. glucose and galactose are Cspecific carbon atom e.g. glucose and galactose are C--4 epimers4 epimersand glucose and mannose are Cand glucose and mannose are C--2 epimers.2 epimers.

E A TIOMERSE A TIOMERS-- a special type of isomerism found in pairs of a special type of isomerism found in pairs of structures that are mirror images of each other. The mirror imagesstructures that are mirror images of each other. The mirror images

are termed as enantiomers and the two members are designated asare termed as enantiomers and the two members are designated asDD-- and Land L-- sugar. The vast majority of sugars in humans are Dsugar. The vast majority of sugars in humans are D--sugars.sugars.

CYCLIZATIO OF SUGARSCYCLIZATIO OF SUGARS-- most monosaccharides with 5 or moremost monosaccharides with 5 or morecarbon atoms are predominately found in a ring form, where thecarbon atoms are predominately found in a ring form, where thealdehyde or ketone group has reacted with an alcoholic group on thealdehyde or ketone group has reacted with an alcoholic group on thesame sugar group to form asame sugar group to form a hemiacetal hemiacetal or or hemiketal hemiketal ring.ring.

PyranosePyranose ringring-- if the ring has 5 carbons and 1 oxygen.if the ring has 5 carbons and 1 oxygen.

FuranoseFuranose ringring-- if the ring is 5if the ring is 5--membered (4 carbons and 1 oxygenmembered (4 carbons and 1 oxygen



2.4.IMPORTA T REACTIO S I MO OSACCHARIDES2.4.IMPORTA T REACTIO S I MO OSACCHARIDES

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

1.1. MutarotationMutarotation

2.2. OxidationOxidation3.3. ReductionReduction

4.4. IsomerizationIsomerization

5.5. EsterificationEsterification

6.6. Glycoside formationGlycoside formation



1.1. MutarotationMutarotation ± ±alfaalfa andand betabeta forms of sugars are readily interconverted whenforms of sugars are readily interconverted whendissolved in water dissolved in water

22 Oxidation and reductionOxidation and reductionin 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 (Raldehyde group (R--CHO) yieldsCHO) yields aldonic acidaldonic acid; of terminal CH2OH; of terminal CH2OH(alcohol) yields(alcohol) yields uronic aciduronic acid; and of both the aldehyde and CH2OH; and of both the aldehyde and CH2OHgivesgives aldaric acidaldaric acid. The carbonyl groups in both aldonic and uronic. The carbonyl groups in both aldonic and uroniccan react with an OH group in the same molecule to form a cycliccan react with an OH group in the same molecule to form a cyclicester ester lactonelactone..

33 REDUCTIOREDUCTIOreduction of the aldehyde and ketone groups of monosacchs yieldreduction of the aldehyde and ketone groups of monosacchs yieldsugar alcohols (sugar alcohols (alditols)alditols) Sugar alcohols e.g.sorbitol, are usedSugar alcohols e.g.sorbitol, are usedcommercially in processing foods and pharmaceuticals.commercially in processing foods and pharmaceuticals.

IMPORTA T REACTIO S I MO OSACCHARIDESIMPORTA T REACTIO S I MO OSACCHARIDES

DetailsDetails



IMPORTA T REACTIO S (Cont)IMPORTA T REACTIO S (Cont)

4.4. ISOMERIZATIOISOMERIZATIO

Monosaccharides undergo several types of isomerization e.g. DMonosaccharides undergo several types of isomerization e.g. D--glucose inglucose inalkaline solution for several hours contain Dalkaline solution for several hours contain D--mannose and Dmannose and D--fructose. Thefructose. Theconversion of glucose to mannose is termed sconversion of glucose to mannose is termed s epimerizationepimerization. (p.208. (p.208--9 of 9 of Textbook).Textbook).

55 ESTERIFICATIOESTERIFICATIO

Free OH groups of carbohydrates react with acids to formFree OH groups of carbohydrates react with acids to form estersesters. This. Thisreaction can change the physical and chemical propteries of sugar.reaction can change the physical and chemical propteries of sugar.Phosphate and sulfate esters of carbohydrates [carbos] are common inPhosphate and sulfate esters of carbohydrates [carbos] are common innature. Phosphorylated derivatives of some carbos, formed duringnature. Phosphorylated derivatives of some carbos, formed duringreactions with ATP, are important metabolic components of living cellsreactions with ATP, are important metabolic components of living cells

6.6. GLYCOSIDE FORMATIOGLYCOSIDE FORMATIO --

Hemiacetals and hemiketals reaction with alcohols to form theHemiacetals and hemiketals reaction with alcohols to form thecorressponding acetal or ketal (p.210 of Text).On the contrary when acorressponding acetal or ketal (p.210 of Text).On the contrary when a cycliccyclichemiacetal or hemiketal form of monosaccharide reacts with alcohol, thehemiacetal or hemiketal form of monosaccharide reacts with alcohol, thenew linkage is callednew linkage is called glyc osidi c l inkag eglyc osidi c l inkag e and the compoundand the compound glyc oside glyc oside [ e.g . gluc osides, f r u tosides, py ranosides] [ e.g . gluc osides, f r u tosides, py ranosides]



Alfa & beta GLYCOCIDIC BO D Alfa & beta GLYCOCIDIC BO D



REDUCI G SUGARSREDUCI G SUGARS

All monosacchs are reducing sugars. All monosacchs are reducing sugars.

They can be oxidised by weak oxidisingThey can be oxidised by weak oxidisingagent such as Benedict¶s reagentagent such as Benedict¶s reagent

Benedict's reagent is a solution of copper Benedict's reagent is a solution of copper sulfate, sodium hydroxide, and tartaricsulfate, sodium hydroxide, and tartaricacid.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 redThe reaction reduces the blue copper (II) ion to form a brick redprecipitate of copper (I) oxide. Because of this, glucose isprecipitate of copper (I) oxide. Because of this, glucose is

classified as a reducing sugar classified as a reducing sugar ..



2.5 IMPORTA T MO OSACCHARIDES

GLUCOSEGLUCOSEFRUCTOSEFRUCTOSE

GALACTOSEGALACTOSE

DD--Glucose: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 splillsCharacterized by high blood glucose levels that splillsover into the urineover into the urine

These high glucose levels impairs the insulinThese high glucose levels impairs the insulin--stimulatedstimulatedglucose entry into cells and starve the cells of insulin.glucose entry into cells and starve the cells of insulin.

This leads toThis leads to ketosisketosis or high levels of ketone bodiesor high levels of ketone bodies

(acids) that hinders the buffering capacity of the blood in(acids) that hinders the buffering capacity of the blood inthe kidney, which controls blood pH (by excreting excessthe kidney, which controls blood pH (by excreting excessH+ ions into the urine).H+ ions into the urine).

The H+ excretion is accompanied by the excretionThe H+ excretion is accompanied by the excretionammonia, sodium,potassium, and phosphate ionsammonia, sodium,potassium, and phosphate ions

causing severe dehydrationcausing severe dehydrationThis leads to excessive thirst symptom of diabetes andThis leads to excessive thirst symptom of diabetes andlifelife--threatening decrease in blood volume.threatening decrease in blood volume.



Important monosaccharides. Cont

FRUCTOSEFRUCTOSE

± ± DD--fructose (levulose) is often referred as fruit sugar 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 ketoseThis molecule is an important member of ketosemember of sugarsmember of sugars

± ± It is twice as sweet as sucrose (per gram basis) and isIt 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 reproductiveIt is present in large amounts in male reproductivetract and is synthesised in the seminal vesicles.tract and is synthesised in the seminal vesicles.



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

GALACTOSEGALACTOSE ± ± is necessary to synthesize a variety of biomoleculesis 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 andGalactose and glucose are epimers at carbon 4 andinterconversion is catalysed by enzymeinterconversion is catalysed by enzyme epimeraseepimerase..

± ± Medical problemsMedical 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 causein the body can cause liver liver

damagedamage,, cataractscataracts, and severe, and severe mental retardationmental retardation



2.7.MO OSACCHARIDE DERVATIVES

URO IC ACIDSURO IC ACIDS ± ± formed when terminalformed when terminalCHCH22OH group of a mono sugar is oxidisedOH group of a mono sugar is oxidised

± ± Important acids in animalsImportant acids in animals ± ± DD--glucuronic acidglucuronic acid

and its epimer Land its epimer L--iduronic acididuronic acid

± ± In liver cells glucuronic acid combines withIn liver cells glucuronic acid combines with

steroids, certain drugs, and bilirubin tosteroids, certain drugs, and bilirubin to

improve water solubility therby helping theimprove water solubility therby helping the

removal of waste products from the bodyremoval of waste products from the body

± ± These acids are abundant in the connectiveThese acids are abundant in the connective

tissue carbohydrate components.tissue carbohydrate components.



Mono sugar derivatives

AMI O SUGARS AMI O SUGARS ± ± ± ± Sugars in which a hydroxyl group (commonSugars in which a hydroxyl group (common

on carbon 2) is replaced by an amino groupon carbon 2) is replaced by an amino group

e.g. De.g. D--glucosamine and Dglucosamine and D--galactosaminegalactosamine

± ± common constituents of complexcommon constituents of complex

carbohydrate molecule found attached tocarbohydrate molecule found attached to

cellular proteins and lipidscellular proteins and lipids

± ± Amino acids are often acetylated e.g. Amino acids are often acetylated e.g. --acetylacetyl--glucosamine.glucosamine.



Mono sugar derivatives

DEOXYSUGARSDEOXYSUGARS ± ± monosaccharides in which anmonosaccharides in which an -- H has replaced anH has replaced an ± ±

OH groupOH group

± ± Important sugars: LImportant sugars: L--fucose (formed from Dfucose (formed from D--mannosemannose

by reduction reactions) and 2by reduction reactions) and 2--deoxydeoxy--DD--riboseribose ± ± LL--fucosefucose ± ± found among carbohydrate components of found among carbohydrate components of

glycoproteins, such as those of the ABO blood groupglycoproteins, such as those of the ABO blood group

determinates on the surface of red blood cellsdeterminates on the surface of red blood cells

± ± 22--deoxyribose is the pentose sugar component of deoxyribose is the pentose sugar component of D A.D A.



GLYCOSIDESGLYCOSIDES

�� MonosaccharidesMonosaccharides can be linked by glycosidic bondscan be linked by glycosidic bonds(joining of 2 hydroxyl groups of sugars by splitting out(joining of 2 hydroxyl groups of sugars by splitting outwater molecule) to create larger structures.water molecule) to create larger structures.

�� DisaccharidesDisaccharides contain 2 monosaccharides e.g. lactosecontain 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 units3 to 12 monosaccharides unitse.g. glycoproteinse.g. glycoproteins

�� PolysaccharidesPolysaccharides ± ± more than 12 monosaccharidesmore than 12 monosaccharidesunits e.g. glycogen (units e.g. glycogen (homopolysacc haridehomopolysacc haride) having) havinghundreds of sugar units; glycosaminoglycanshundreds of sugar units; glycosaminoglycans

((heteropolysacc haridesheteropolysacc harides) containing a number of different) containing a number of differentmonosaccharides speciesmonosaccharides species..



Section 3Section 3

DISACCHARIDESDISACCHARIDES A D A D

OLIGOSACCHARIDESOLIGOSACCHARIDES



DISACCHARIDES A DDISACCHARIDES A D

OLIGOSACCHARIDESOLIGOSACCHARIDES

Cnfigurations:Cnfigurations: alf aalf a or or betabeta ( 1,4, glycosidic( 1,4, glycosidicbonds 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. DefficiencyDigestion aided by enzymes. Defficiencyof any one enzyme causes unpleasantof any one enzyme causes unpleasantsymptoms (symptoms (fermentationfermentation) in colon) in colonproduces gas [bloating of cramps].produces gas [bloating of cramps].

Most common defficiency, an ancestoralMost common defficiency, an ancestoraldisorder,disorder, lactose intolerancelactose intolerance caused bycaused byreduced synthesis of lactasereduced synthesis of lactase



Important sugars of DisaccharidesImportant sugars of Disaccharides

LACTOSELACTOSE(milk sugar) disaccharide found in milk; composed of one(milk sugar) disaccharide found in milk; composed of one

molecule of galactose and glucose linked throughmolecule of galactose and glucose linked through betabeta(1,4)(1,4)

glycosidic linkage; because of the hemiacetal group of theglycosidic 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 byLactose (milk sugar) in infants is hydrolyzed byintestinal enzyme lactase to its componentintestinal enzyme lactase to its componentmonosacch for absorption into the bloodstreammonosacch for absorption into the bloodstream(galactose epimerized to glucose).(galactose epimerized to glucose).

Most adult mammals have low levels of betaMost adult mammals have low levels of beta--galactosidase. Hence, much of the lactose theygalactosidase. Hence, much of the lactose theyingest moves to the colon, where bacterialingest moves to the colon, where bacterialfermentation 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 upsetThese products cause painful digestive upsetknown asknown as l ac tose intol eranc el ac tose intol eranc e and is commonand is commonin 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 Dglycosidic linkage between two D--glucose molecules; in solution the freeglucose 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 andand betabeta ± ± maltoses; it does not occur freely in naturemaltoses; it does not occur freely in nature



SUCROSESUCROSE

common table sugar: cane sugar or beet sugar producedcommon table sugar: cane sugar or beet sugar producedin the leaves and stems of plants; it is a disaccharidein the leaves and stems of plants; it is a disaccharidecontaining both alfacontaining both alfa--glucose and betaglucose and beta--fructose residuesfructose residueslinked bylinked by alfa,betaalfa,beta(1,2)glycosidic bond.(1,2)glycosidic bond.



CELLOBIOSECELLOBIOSE

degradation product of cellulosedegradation product of cellulose

containing two molecules of glucose linkedcontaining two molecules of glucose linkedby aby 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 oftenOligosaccharides are small polymers oftenfound attached to polypeptides infound attached to polypeptides in

glycoproteinsglycoproteins and someand some glycolipidsglycolipids..

They are attached to membrane andThey are attached to membrane andsecretory proteins found in endoplasmicsecretory proteins found in endoplasmic

reticulum and Golgi complex of variousreticulum and Golgi complex of various

cellscells

Two classes:Two classes: --linked and Olinked and O--linkedlinked



Section 4Section 4POLYSACCHARIDESPOLYSACCHARIDES

4.1. Intro to Polysaccharides4.1. Intro to Polysaccharides

4.2. Classification of Polisacharides4.2. Classification of Polisacharides

4.2.1. Homosacharides4.2.1. Homosacharides

4.2.2.4.2.2. HeteropolysacharidesHeteropolysacharides



4.1. Intro to Polysaccharides4.1. Intro to Polysaccharides

Composed of large number of monosaccharide unitsComposed of large number of monosaccharide unitsconnected by glycosidic linkagesconnected by glycosidic linkages

Classified on the basis of their main monosaccharideClassified on the basis of their main monosaccharidecomponents and the sequences and linkages betweencomponents and the sequences and linkages betweenthem, as well as the anomeric configuration of linkages,them, as well as the anomeric configuration of linkages,the ring size (furanose or pyranose), the absolutethe ring size (furanose or pyranose), the absolute

configuration (Dconfiguration (D-- or Lor L--) and any other substituents) and any other substituentspresent.present. (http://www.lsbu.ac.uk/water/hypol.html)(http://www.lsbu.ac.uk/water/hypol.html)

Polysaccharides are more hydrophobic if they have aPolysaccharides are more hydrophobic if they have agreater number of internal hydrogen bonds, and as their greater number of internal hydrogen bonds, and as their hydrophobicity increases there is less direct interactionhydrophobicity increases there is less direct interaction

with water with water Divided intoDivided into homopolysacc harideshomopolysacc harides (e.g.Starch, glycogen,(e.g.Starch, glycogen,cellulose, and chitin) &cellulose, and chitin) & heteropolysacc haridesheteropolysacc harides(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 nature

Important examples: starch, glycogen, cellulose,Important examples: starch, glycogen, cellulose,and chitinand chitin

Starch, glycogen, and cellulose all yield DStarch, glycogen, and cellulose all yield D--glucose when they are hydrolyzedglucose when they are hydrolyzed

CelluloseCellulose -- primary component of plant cellsprimary component of plant cells

ChitinChitin ± ± principal structural component of principal structural component of

exoskeletons of arthropods and cell walls of exoskeletons of arthropods and cell walls of many fungi; yield glucose derivativemany fungi; yield glucose derivative --acetylacetylglucosamine when it is hydrolyzed.glucosamine when it is hydrolyzed.



STARCH (Homosaccharide)STARCH (Homosaccharide)

A naturally abundant nutrient carbohydrate, (C A naturally abundant nutrient carbohydrate, (C66HH1010OO55)n, found)n, foundchiefly 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 innotably in corn, potatoes, wheat, and rice, and varying widely inappearance according to source but commonly prepared as a whiteappearance according to source but commonly prepared as a whiteamorphous 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 stiffencloth, as in laundering.cloth, as in laundering.

Two polysaccharides occur together in starch: amylose andTwo polysaccharides occur together in starch: amylose andamylopectinamylopectin

Amylose Amylose ± ± unbranched chains of Dunbranched chains of D--glucose residues linked withglucose residues linked withalfa( alfa( 1,4,)glycosidic bonds1,4,)glycosidic bonds

Amylopectin Amylopectin ± ± a branched polymer containing botha branched polymer containing both alfaalfa(1,4,) and(1,4,) andalfa(1,6) glcosidic linkages; thealfa(1,6) glcosidic linkages; the alfa( alfa( 1,6) branch points may occur 1,6) branch points may occur

every 20every 20--25 glucose residues to prevent helix formation25 glucose residues to prevent helix formationStarch digestion begins in the mouth; alfaStarch digestion begins in the mouth; alfa--amylase in the salivaamylase in the salivainitiates hydrolysis of the gycosidic linkagesinitiates hydrolysis of the gycosidic linkages



GLYCOGE (Homosaccharide)GLYCOGE (Homosaccharide)

Glycogen is the storage form of glucose in animals and humansGlycogen 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 theGlycogen is synthesized and stored mainly in the liver and themuscles.muscles.

Structurally, glycogen is very similar to amylopectin with alphaStructurally, glycogen is very similar to amylopectin with alphaacetal linkages, however, it has even more branching and moreacetal linkages, however, it has even more branching and moreglucose units are present than in amylopectin.glucose units are present than in amylopectin.

Various samples of glycogen have been measured at 1,700Various 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 glucoseThe structure of glycogen consists of long polymer chains of glucoseunits connected by anunits connected by an alpha acetalalpha acetal linkage.linkage.

The branches are formed by linking C # 1 to a C # 6 through anThe branches are formed by linking C # 1 to a C # 6 through anacetal linkages.acetal linkages.

In glycogen, the branches occur at intervals of 8In glycogen, the branches occur at intervals of 8--10 glucose units,10 glucose units,while in amylopectin the branches are separated by 12while in amylopectin the branches are separated by 12--20 glucose20 glucoseunits.units.



STRUCTURE OF GLYCOGESTRUCTURE OF GLYCOGE



CELLULOSE (Homosaccharide)CELLULOSE (Homosaccharide)

Cellulose is found in plants as microfibrils (2Cellulose is found in plants as microfibrils (2--20 nm diameter and20 nm diameter and100100 -- 40 000 nm long). These form the structurally40 000 nm long). These form the structurallystrongstrong framework in the cell walls.framework in the cell walls.

Cellulose is mostly prepared from wood pulpCellulose is mostly prepared from wood pulp

Cellulose is a linear polymer of Cellulose is a linear polymer of --(1 4)(1 4)--DD--glucopyranose units inglucopyranose units in 44CC11

conformation. The fully equatorial conformation of conformation. The fully equatorial conformation of --linkedlinkedglucopyranose residues stabilizes the chair structure, minimizing itsglucopyranose residues stabilizes the chair structure, minimizing itsflexibilityflexibility

Cellulose 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 aredispersing agent, thickener, and gelling agent but these aregenerally 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 amorphousWater cannot penetrate crystalline cellulose but dry amorphouscellulose 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 water--soluble derivatives e.g. Methyl cellulose, carbomethycellulosesoluble derivatives e.g. Methyl cellulose, carbomethycellulose



Cellulose as polymer of Cellulose as polymer of --DD--glucoseglucose



Cellulose in 3DCellulose in 3D



CELLULOSECELLULOSE



CHITI (Homosaccharide)CHITI (Homosaccharide)

Chitin is a polymer that can be found in anything fromChitin is a polymer that can be found in anything fromthe shells of beetlesto webs of spiders. It is present allthe shells of beetlesto webs of spiders. It is present allaround 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 containsCellulose contains a hydroxy group, and chitin containsacetamide.acetamide.

Chitin is unusual because it is a "natural polymer," or aChitin is unusual because it is a "natural polymer," or acombination of elements that exists naturally on earth.combination of elements that exists naturally on earth.

Usually, polymers are manUsually, polymers are man--made. Crabs, beetles, wormsmade. 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 insectChitin is a very firm material, and it help protect an insectagainst harm and pressureagainst harm and pressure



Structure of the chitin molecule, showing two of theStructure of the chitin molecule, showing two of the --

acetylglucosamine units that repeat to form long chains inacetylglucosamine units that repeat to form long chains in

betabeta--1,4 linkage.1,4 linkage.



CHITOSACHITOSA

A spinoff of chitin that has been discovered by the A spinoff of chitin that has been discovered by themarket is chitosan. This is a manmarket is chitosan. This is a man--made molecule that ismade molecule that isoften used to dye shirts and jeans in the clothingoften used to dye shirts and jeans in the clothingindustry.industry.

Chitosan can be used within the human body to regulateChitosan can be used within the human body to regulate

diet programs, and researchers are looking into ways indiet programs, and researchers are looking into ways inwhich it can sure diseases.which it can sure diseases.

Chitin, the polysaccharide polymer from which chitosanChitin, the polysaccharide polymer from which chitosanis derived, is a celluloseis derived, is a cellulose--like polymer consisting mainly of like polymer consisting mainly of unbranched chains of unbranched chains of --acetylacetyl--DD--glucosamine.glucosamine.

Deacetylated chitin, or chitosan, is comprised of chainsDeacetylated chitin, or chitosan, is comprised of chainsof Dof D--glucosamine. When ingested, chitosan can beglucosamine. When ingested, chitosan can beconsidered a dietary fiber.considered a dietary fiber.



CHEMICAL STRUCTURE OF CHITOSACHEMICAL STRUCTURE OF CHITOSAhttp://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 Are high--molecular molecular--weight carbohydrateweight carbohydrate

polymers more than one kind of polymers more than one kind of

monosaccharidemonosaccharide

Important examples includeImportant examples include

glycosaminoglycans (GAGs)glycosaminoglycans (GAGs) ± ± thethe

principle components of proteoglycansprinciple components of proteoglycans

and murein, a major component of and murein, a major component of bacterial cell walls.bacterial cell walls.

GAGGAG hi hhi h l ll l i hi h



GAGsGAGs -- highhigh--molecular molecular--weightweight

carbohydrate polymerscarbohydrate polymers

GlycosaminoglycansGlycosaminoglycans forming theforming theproteoglycans are the most abundantproteoglycans are the most abundant

heteropoly sacc haridesheteropoly sacc harides in the body. They arein the body. They are

long unbranched molecules containing along unbranched molecules containing a

repeating disacc haride unit repeating disacc haride unit . Usually one sugar is. Usually one sugar isan uronic acid (either an uronic acid (either DD--glucuronic glucuronic or or LL--iduronic iduronic ))

and the other is either and the other is either GlcNAc GlcNAc or or GalNAc GalNAc . One. One

or both sugars contain sulfate groups (the onlyor both sugars contain sulfate groups (the only

exception is hyaluronic acid).exception is hyaluronic acid).GAGs are highly negatively charged what isGAGs are highly negatively charged what is

essential for their function.essential for their function.



THE SPECIFIC GAGs OF PHYSIOLOGICALTHE SPECIFIC GAGs OF PHYSIOLOGICAL

SIGNIFICANCE SIGNIFICANCE

Hyaluronic acidHyaluronic acidOccurenceOccurence : synovial fluid, ECM of loose: synovial fluid, ECM of looseconnective tissueconnective tissueHyaluronic acidHyaluronic acid is unique among the GAGsis unique among the GAGsbecause it does not contain any sulfate and isbecause it does not contain any sulfate and isnot found covalently attached to proteins. Itnot found covalently attached to proteins. Itforms nonforms non--covalently linked complexescovalently linked complexes withwithproteoglycansproteoglycans in the ECM.in the ECM.

Hyaluronic acid polymers are very large (100Hyaluronic 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(D--glucuronate + Glc Ac)glucuronate + Glc Ac)



Dermatan sulfateDermatan sulfate (L(L--iduronate + Glc Ac sulfate)iduronate + Glc Ac sulfate)

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

Chondroitin sulfateChondroitin sulfate (D(D glucuronate +glucuronate +



Chondroitin sulfateChondroitin sulfate (D(D--glucuronate +glucuronate +

Gal Ac sulfate)Gal Ac 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 sulfateHeparin and heparan sulfate (D(D--glucuronateglucuronate

sulfate +sulfate + --sulfosulfo--DD--glucosamine)glucosamine)

Heparans have less sulfate groups than heparinsHeparans have less sulfate groups than heparinsOccurenceOccurence ::HeparinHeparin :component of intracellular granules of mast cells lining the:component of intracellular granules of mast cells lining thearteries of the lungs, liver and skinarteries of the lungs, liver and skin Heparan sulfateHeparan sulfate : basement: basement

membranes, component of cell surfacesmembranes, component of cell surfaces



Keratan sulfateKeratan sulfate ( Gal + Glc Ac sulfate)( Gal + Glc Ac sulfate)

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

Keratan sulfates are often aggregated with chondroitinKeratan sulfates are often aggregated with chondroitin

sulfatessulfates..



MUREI (Peptidoglycan)MUREI (Peptidoglycan)

PeptidoglycanPeptidoglycan, also known as, also known as mureinmurein, is a, is a polymer polymer consisting of consisting of sugars and amino acids that forms a meshsugars and amino acids that forms a mesh--like layer outside thelike layer outside theplasma membraneplasma membrane of of eubacteriaeubacteria..

The sugar component consists of alternating residues of The sugar component consists of alternating residues of --(1,4)(1,4)linkedlinked --acetylglucosamine andacetylglucosamine and --acetylmuramic acid residues.acetylmuramic acid residues.

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

The peptide chain can be crossThe peptide chain can be cross--linked to the peptide chain of linked to the peptide chain of

another strand forming the 3D meshanother strand forming the 3D mesh--like layer.like layer.

SomeSome Archaea Archaea have a similar layer of have a similar layer of pseudopeptidoglycanpseudopeptidoglycan..



Peptidoglycan serves a structural role in the bacterialPeptidoglycan serves a structural role in the bacterial cellcellwallwall, giving the wall shape and structural strength, as, giving the wall shape and structural strength, aswell as counteracting thewell as counteracting the osmotic pressureosmotic pressure of theof the

cytoplasmcytoplasm..

Peptidoglycan is also involved inPeptidoglycan is also involved in binary fissionbinary fission duringduringbacterial cell reproduction.bacterial cell reproduction.

The peptidoglycan layer is substantially thicker inThe peptidoglycan layer is substantially thicker in GramGram--positivepositive bacteriabacteria (20 to 80(20 to 80 nmnm) than in) than in GramGram--negativenegativebacteria (7 to 8 nm), with the attachment of thebacteria (7 to 8 nm), with the attachment of the SS--layer layer ..

Peptidoglycan forms around 90% of the dry weight of Peptidoglycan forms around 90% of the dry weight of

GramGram--positive bacteria but only 10% of Grampositive bacteria but only 10% of Gram--negativenegativestrains.strains.

In GramIn Gram--positive strains, it is important in attachmentpositive strains, it is important in attachmentroles and serotyping purposes.roles and serotyping purposes.



SECTIO 5SECTIO 5

GLYCOCO JUGATESGLYCOCO JUGATES5.1.5.1. Intro to glycoconjugatesIntro to glycoconjugates

5.2.5.2. glycoproteinsglycoproteins

5.3.5.3. glycosylationglycosylation

5.4.5.4. proteoglycansproteoglycans



5.1. Intro to glycoconjugates5.1. Intro to glycoconjugates

They are compounds that result from covalentThey are compounds that result from covalentlinkages of carbohydrate molecules to bothlinkages of carbohydrate molecules to bothproteins 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 cellindividual cells as weell as cell--cell interactionscell interactionsof multicellular organisms.of multicellular organisms.

Two classes of carbohydrateTwo classes of carbohydrate--protein conjugate:protein conjugate:glycoproteinsglycoproteins andand proteoglycans.proteoglycans.

TheThe glycolipidsglycolipids (oligosaccharide(oligosaccharide--containing lipidcontaining lipidmolecules) 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 byThey are formed by glyc osyl ationglyc osyl ation and classified intoand classified intotwo groups:two groups:

1.1. --linked oligosaccharideslinked oligosaccharides

2. O2. O--linked oligosaccharideslinked oligosaccharides

TheThe --linked oligosaccharides have a minimum of 5linked oligosaccharides have a minimum of 5

sugar residuessugar residues--linked attached to polypeptides by anlinked attached to polypeptides by an N N--glycosidic glycosidic bond bond with a chain amide group of amino acid andwith a chain amide group of amino acid andasparagineasparagine

OO--linked oligosaccharides are generally short (1linked oligosaccharides are generally short (1--4 sugar 4 sugar residues)residues)

OO--linked arelinked are attached to polypeptides by the side chainattached to polypeptides by the side chainhydroxyl group of amino acidshydroxyl group of amino acids serine or threonine inserine or threonine inpolypeptide chains or hydroxyl groups of membranepolypeptide chains or hydroxyl groups of membranelipidslipids



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 proteins

Majority of proteins synthesized in the rough ER undergoMajority of proteins synthesized in the rough ER undergoglycosylationglycosylation

It is an enzymeIt is an enzyme --directed sitedirected site--specific process.specific process.Two types of glycosylation exist:Two types of glycosylation exist: N N --linkedlinked glycosylationglycosylationto theto the amide nitrogenamide nitrogen of asparagine side chains andof asparagine side chains and O O --linkedlinked glycosylation to theglycosylation to the hydroxy oxygenhydroxy oxygen of of serineserine andandthreoninethreonine side chains.side chains.

Glycosylation may play a role in cellGlycosylation may play a role in cell--cell adhesion (acell adhesion (amechanism employed by cells of themechanism employed by cells of the immune systemimmune system),),as well.as well.



GLYCOPROTEI FU CTIO SGLYCOPROTEI FU CTIO STypes of glycoproteins: asparagineTypes of glycoproteins: asparagine--linked carbohydrate;linked carbohydrate;

mucinmucin--type cabohydratetype cabohydrateExamples:Examples: glycophoringlycophorin (membrane protein, source(membrane protein, source ± ±human RBC, % carbohydratehuman RBC, % carbohydrate -- 60);60); potato lectin potato lectin (lectin,(lectin,carbohydrate binding proteins, sourcecarbohydrate binding proteins, source ± ± potato, %potato, %carbohydratecarbohydrate ± ± 50)50)

FunctionsFunctions: Many glycoproteins have: Many glycoproteins have structuralstructuralfunctions: constituent of thefunctions: constituent of the cell wallcell wall; form; form connectiveconnectivetissuestissues such as collagen; found in gastrointestinalsuch as collagen; found in gastrointestinal mucusmucussecretions;secretions; used asused as protectiveprotective agents and lubricantsagents and lubricants;found abundantly in the;found abundantly in the blood plasmablood plasma..

The human blood groups A, B, AB, and O depend on theThe human blood groups A, B, AB, and O depend on theoligosaccharide part of the glycoprotein on the surfaceoligosaccharide part of the glycoprotein on the surfaceof erythrocyte cells. The terminal monosaccharide of theof erythrocyte cells. The terminal monosaccharide of theglycoprotein at the nonreducing end determines bloodglycoprotein at the nonreducing end determines bloodgroup.group.



BLOOD GROUPSBLOOD GROUPS

TYPETYPE TERMINAL SUGARTERMINAL SUGARAA NN--acetylgalactosamineacetylgalactosamine

BB EE--DD--galactosegalactose

ABAB both the aboveboth the aboveOO neither of the aboveneither of the above

OO is the ³universal donor´is the ³universal donor´

ABAB is the ³universalis the ³universalacceptor´acceptor´



Oligosaccharides are antigeneicOligosaccharides are antigeneic

determinantsdeterminants

Carbohydrates on cell surfaces areCarbohydrates on cell surfaces areimmunochemical markers.immunochemical markers.

ABO blood group antigensABO blood group antigens areare

oligosaccharide components of glycoproteinsoligosaccharide components of glycoproteinsand glycolipids on the surfaces of individualand glycolipids on the surfaces of individualcells, besides blood cells.cells, besides blood cells.

Individuals with type A cells have A antigens onIndividuals with type A cells have A antigens ontheir cell surfaces and carry antitheir cell surfaces and carry anti--B antibodiesB antibodies

Those with type B cells which bear B antigens,Those with type B cells which bear B antigens,carry anticarry anti--A antibodies A antibodies



Those with type AB cells, which have both A andThose with type AB cells, which have both A and

B antigens, carry neither antiB antigens, carry neither anti--A nor anti A nor anti--BB

antibodiesantibodies

Type O individuals whose cells bear neither Type O individuals whose cells bear neither

antigen, carry both antiantigen, carry both anti--A and anti A and anti--B antibodies.B antibodies.

Transfusion of type A blood group into a type BTransfusion of type A blood group into a type Bindividual, results in an antiindividual, results in an anti--A antibody A antibody-- A A

antigen reaction.antigen reaction.

This reaction clumps together (agglutinates) theThis reaction clumps together (agglutinates) the

transfused erythrocytes, resulting in an oftentransfused erythrocytes, resulting in an oftenfatal blockage of blood vesselsfatal blockage of blood vessels



Functions of glycoproteins (elaborated)Functions of glycoproteins (elaborated)http://www.cs.stedwards.edu/chem/Chemistry/C HEM43/CHEM43/Glycoproteins/Glycoproteins.HTMLhttp://www.cs.stedwards.edu/chem/Chemistry/C HEM43/CHEM43/Glycoproteins/Glycoproteins.HTML

Carbohydrates and proteins by themselves serve in a vastCarbohydrates and proteins by themselves serve in a vastnumber of biological functions,linking the two together number of biological functions,linking the two together results in a macromolecule with an extremely largeresults in a macromolecule with an extremely largenumber of functions.number of functions.

StructuralStructural: Glycoproteins are found throughout: Glycoproteins are found throughoutmatrices. They act as receptors on cell surfaces thatmatrices. They act as receptors on cell surfaces that

bring other cells and proteins (collagen) together givingbring other cells and proteins (collagen) together givingstrength and support to a matrix.strength and support to a matrix.

In nerve tissue glycoproteins are abundant in grayIn nerve tissue glycoproteins are abundant in graymatter and appear to be associated with synaptosomes,matter and appear to be associated with synaptosomes,axons, and microsomes.axons, and microsomes.

Protection

Protection: Human lacrimal glands produce a: Human lacrimal glands produce aglycoprotein which protects the corneal epithelium fromglycoprotein which protects the corneal epithelium from

desiccation and foreign particles. Human sweat glandsdesiccation and foreign particles. Human sweat glandssecrete glycoproteins which protect the skin from thesecrete glycoproteins which protect the skin from theother excretory products that could harm the skinother excretory products that could harm the skin



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

Prothrombin, thrombin, and fibrinogen are allProthrombin, thrombin, and fibrinogen are all

glycoproteins that play an intricate role in the bloodglycoproteins that play an intricate role in the bloodclotting mechanismclotting mechanism

In certain bacteria the slime layer that surrounds theIn certain bacteria the slime layer that surrounds theoutermost components of cell walls are made up of outermost components of cell walls are made up of glycoproteins of high molecular weight. In addition toglycoproteins of high molecular weight. In addition to

forming these sforming these s--layers, glycoproteins also function aslayers, glycoproteins also function asbacterial 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 attractionspermatozoa appear to increase a sperm cell's attractionfor the egg by altering the electrophoretic mobility of thefor the egg by altering the electrophoretic mobility of theplasma membrane.plasma membrane.




Adhesion

Adhesion: Glycoproteins serve to adhere cells: Glycoproteins serve to adhere cellsto cells and cells to substratum.to cells and cells to substratum.

HormonesHormones: There are many glycoproteins that: There are many glycoproteins thatfunction as hormones such as human chorionicfunction as hormones such as human chorionicgonadotropin (HCG) which is present in humangonadotropin (HCG) which is present in humanpregnancy urine. Another example ispregnancy urine. Another example iserythropoietin which regulates erythrocyteerythropoietin which regulates erythrocyteproductionproduction

Enzymes: Glycoprotein enzymes are of threeEnzymes: Glycoprotein enzymes are of threetypes. These are oxidoreductases, transferases,types. These are oxidoreductases, transferases,and hydrolases.and hydrolases.




CarriersCarriers: Glycoproteins can bind to certain molecules: Glycoproteins can bind to certain molecules

and serve as vehicles of transport. They can bind toand serve as vehicles of transport. They can bind tovitamins, hormones, cations, and other substances.vitamins, hormones, cations, and other substances.

InhibitorsInhibitors: Many glycoproteins in blood plasma have: Many glycoproteins in blood plasma haveshown antiproteolytic activity. For example, theshown antiproteolytic activity. For example, theglycoprotein a1glycoprotein a1--antichymotrypsin inhibits chymotrypsin.antichymotrypsin inhibits chymotrypsin.

Immunological

Immunological: The interaction of blood group: The interaction of blood groupsubstances with antibodies is determined by thesubstances with antibodies is determined by theglycoproteins on erythrocytes. Many immunoglobulinsglycoproteins on erythrocytes. Many immunoglobulinsare actually glycoproteins.are actually glycoproteins.

B and T cells contain surface glycoproteins that attractB and T cells contain surface glycoproteins that attractbacteria to these sites and bind them. In much the samebacteria to these sites and bind them. In much the same

manner, glycoproteins can direct phagocytosis. Becausemanner, glycoproteins can direct phagocytosis. Becausethe HIV virus recognizes the receptor protein CD4, itthe HIV virus recognizes the receptor protein CD4, itbinds to helper T cells which contain it.binds to helper T cells which contain it.



CELL MEMBRA ECELL MEMBRA E

The 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 branchedMembrane carbohydrates are usually branchedoligosaccharides with fewer than 15 sugar units.oligosaccharides with fewer than 15 sugar units.

Some of these oligosaccharides are covalently bondedSome of these oligosaccharides are covalently bondedto lipids, forming molecules calledto lipids, forming molecules called glycolipids.glycolipids.

Most are covalently bonded to proteins, which areMost are covalently bonded to proteins, which aretherebythereby glycoproteinsglycoproteins..

Plants producePlants produce pectinpectin, major component of cell wall., major component of cell wall.

The oligosaccharides on the external side of the plasmaThe oligosaccharides on the external side of the plasmamembrane vary from species to speciesmembrane vary from species to species

The diversity of the molecules and their location on theThe diversity of the molecules and their location on thecell's surface enable oligosaccharides to function ascell's surface enable oligosaccharides to function asmarkers that distinguish one cell from another.markers that distinguish one cell from another.



THE MOSAIC OF CELL¶S MEMBRA ETHE MOSAIC OF CELL¶S MEMBRA E



CELL MEMBRA E MATRIXCELL MEMBRA E MATRIX

The biological membrane is a collage of manyThe biological membrane is a collage of manydifferentdifferent proteinsproteins embedded in the fluid matrixembedded in the fluid matrixof theof the lipid bilayer lipid bilayer ..

TheThe lipid bilayer lipid bilayer is the main fabric of theis the main fabric of the

membrane, and its structure creates a semimembrane, 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 itwhich can dissolve in the membrane, cross itwith ease.with ease.



Protein layer of cell membraneProtein layer of cell membrane

Proteins determine most of theProteins determine most of themembrane's specific functions.membrane's specific functions.

The plasma membrane and theThe plasma membrane and themembranes of the various organelles eachmembranes of the various organelles eachhave unique collections of proteins.have unique collections of proteins.

For example, to date more than 50 kindsFor example, to date more than 50 kindsof proteins have been found in the plasmaof proteins have been found in the plasmamembrane of red blood cells.membrane of red blood cells.



5. . PR TE G Y AN5. . PR TE G Y AN

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 moreThey consist of a core protein with one or morecovalently attached glycosaminoglycan chain(s).covalently attached glycosaminoglycan chain(s).

TheseThese glycosaminoglycan (GAG) chainsglycosaminoglycan (GAG) chains are long, linear are long, linear carbohydrate polymers that are negatively chargedcarbohydrate polymers that are negatively chargedunder 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 theProteoglycans can be categorised depending upon thenature of their glycosaminoglycan chains. These chainsnature of their glycosaminoglycan chains. These chainsmay be:may be:

1. chondroitin sulfate and dematan sulfate1. chondroitin sulfate and dematan sulfate2. heparin and heparin sulfate2. heparin and heparin sulfate

3. keratan sulfate3. keratan sulfate



Proteoglycans can also be categorised byProteoglycans can also be categorised by

size.size.Example of Example of largelarge proteoglycan isproteoglycan is

aggrecan.aggrecan.

Aggrecan Aggrecan, is the major proteoglycan in, is the major proteoglycan incartilage, present in many adult tissuescartilage, present in many adult tissues

including blood vessels and skin.including blood vessels and skin.

TheThe smallsmall leucine rich repeatleucine rich repeat

proteoglycans (SLRPs) includeproteoglycans (SLRPs) include decorin,decorin,

biglycan, fibromodulinbiglycan, fibromodulin andand lumicanlumican..



SY THESIS OF PROTEOGLYCA SSY THESIS OF PROTEOGLYCA S

The protein component of proteoglycans isThe protein component of proteoglycans issynthesized bysynthesized by ribosomesribosomes andand translocatedtranslocated intointothe lumen of thethe lumen of the rough endoplasmic reticulumrough endoplasmic reticulum..

Glycosylation of the proteoglycan occurs in theGlycosylation of the proteoglycan occurs in theGolgi apparatusGolgi apparatus in multiplein multiple enzymaticenzymatic steps.steps.

First a special link tetrasaccharide is attached toFirst a special link tetrasaccharide is attached toaa serineserine side chain on the core protein to serveside chain on the core protein to serveas a primer for polysaccharide growth.as a primer for polysaccharide growth.

Then sugars are added one at the time byThen sugars are added one at the time byglycosyl transferase.glycosyl transferase.

The completed proteoglycan is then exported inThe completed proteoglycan is then exported insecretorysecretory vesiclesvesicles to the extracellular matrix of to the extracellular matrix of the cell.the cell.



Structure of proteoglycansStructure of proteoglycans

The GAGs extend perpendicular from the core protein in aThe GAGs extend perpendicular from the core protein in a

bottlebrushbottlebrush-- like structure.like structure.

The linkage of GAGs such as (The linkage of GAGs such as (heparan sulfates and c hondroitinheparan sulfates and c hondroitinsulfatessulfates) to the protein core involves a specific trisaccharide linker ) to the protein core involves a specific trisaccharide linker

Some forms of Some forms of keratan sulfateskeratan sulfates are linked to the protein coreare linked to the protein corethrough anthrough an NN--asparaginylasparaginyl bondbond..

The protein cores of proteoglycans are rich in Ser and Thr residuesThe protein cores of proteoglycans are rich in Ser and Thr residueswhich allows multiple GAG attachment.which allows multiple GAG attachment.



FU CTIO OF PROTEOGLYCA SFU CTIO OF PROTEOGLYCA S

Proteoglycans are a major component of the animalProteoglycans are a major component of the animalextracellular matrixextracellular matrix, the 'filler' substance existing, the 'filler' substance existingbetweenbetween cellscells in an organism.in an organism.

Individual functions of proteoglycans can be attributed toIndividual functions of proteoglycans can be attributed toeither the protein core or the attached GAG chain.either the protein core or the attached GAG chain.

In extracellular matrix, they form large complexes, withIn extracellular matrix, they form large complexes, withother proteoglycans, toother proteoglycans, to hyaluronanhyaluronan and to fibrous matrixand to fibrous matrixproteins (such asproteins (such as collagencollagen).).

They are also involved in bindingThey are also involved in binding cationscations (such as(such assodiumsodium,, potassiumpotassium andand calciumcalcium) and) and water water , and also, and also

regulating the movement of molecules through theregulating the movement of molecules through thematrix.matrix.

They can affect the activity and stability of proteins andThey can affect the activity and stability of proteins andsignalling molecules within the matrix.signalling molecules within the matrix.

ROLE OF PROTEOGLYCANSROLE OF PROTEOGLYCANS



ROLE OF PROTEOGL YCANSROLE OF PROTEOGL YCANShttp://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 twodependent functions can be divided into two

classes: the biophysical and the biochemical.classes: the biophysical and the biochemical.

TheThe biophysical functionsbiophysical functions depend on the uniquedepend on the uniqueproperties of GAGs : the ability to fill the space, bind andproperties of GAGs : the ability to fill the space, bind andorganize water molecules and repel negatively chargedorganize water molecules and repel negatively charged

molecules. Because of high viscosity and lowmolecules. Because of high viscosity and lowcompressibility they are ideal for a lubricating fluid in thecompressibility 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 structuralintegrity to the cells and allows the cell migration due tointegrity to the cells and allows the cell migration due toproviding the passageways between cells.providing the passageways between cells.

For example the large quantities of For example the large quantities of chondroitin sulfatechondroitin sulfateand keratan sulfateand keratan sulfate found onfound on agg rec anagg rec an play anplay animportant role in theimportant role in the hydration of cartilagehydration of cartilage. They give. They givethe cartilage its gelthe cartilage its gel--like properties and resistance tolike properties and resistance todeformation.deformation.



Role of proteoglycans contd.Role of proteoglycans contd.

The other, more biochemical functions of GAGsThe other, more biochemical functions of GAGsare mediated by specific binding of GAGs toare mediated by specific binding of GAGs toother macromolecules, mostly proteins.other macromolecules, mostly proteins.Proteoglycans participate in cell and tissueProteoglycans participate in cell and tissuedevelopment and physiology.development and physiology.

Hurler¶s syndrome: (refer Text) disease relatedHurler¶s syndrome: (refer Text) disease relatedwith proteoglycan metabolism where excessivewith proteoglycan metabolism where excessiveaccumulation of dermatin sulfate due toaccumulation of dermatin sulfate due to

deficiency of a specific enzyme may causedeficiency of a specific enzyme may causemental retardation, skeletal deformity ansdmental retardation, skeletal deformity ansddeath in early childhood.death in early childhood.

SUMMARYSUMMARY



SUMMARYSUMMARYMonosaccharides, the simplest carbohydrates, areMonosaccharides, 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 atmonosacchs have either alfa or beta configuration attheir anomeric carbon.their anomeric carbon.

Monosacch derivatives include aldonic acids, uronicMonosacch derivatives include aldonic acids, uronic

acids, deoxy sugars, amino sugars, alfa & betaacids, deoxy sugars, amino sugars, alfa & betaglycosides.glycosides.

Disaccharides simplest polysaccharides occuring asDisaccharides simplest polysaccharides occuring ashydrolysis products of larger molecules e.g.hydrolysis products of larger molecules e.g.Lactose,sucroseLactose,sucrose

Oligosaccharides play important roles in determiningOligosaccharides play important roles in determiningprotein structure and in cellprotein structure and in cell--surface recognitionsurface recognitionphenomena. Oligosacchs with 3 or more sugar residuesphenomena. Oligosacchs with 3 or more sugar residuesare mostly found in plants.are mostly found in plants.

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Summary contd.Summary contd. --11

POLOYSACCHARIDES consist of monosacchsPOLOYSACCHARIDES consist of monosacchslinked by glycosidic bonds.linked by glycosidic bonds.

Cellulose and chitin areCellulose and chitin are str uc t u ral poly sacc hsstr uc t u ral poly sacc hswith beta(1with beta(1--4) linkages that adopt rigid and4) linkages that adopt rigid andextended structures.extended structures.

TheThe storag e poly sacc hsstorag e poly sacc hs starch and glycogenstarch and glycogenconsist of alfaconsist of alfa--glycosidically linked glucoseglycosidically linked glucoseresiduesresidues

G lyc osaminoglyc ans G lyc osaminoglyc ans are unbranchedare unbranchedpolysacchs containing uronic acids and aminopolysacchs containing uronic acids and aminosugars that are often sulfatedsugars that are often sulfated

Summary contdSummary contd 22



Summary contd.Summary contd.--22

GL YCOCONJUGATESGL YCOCONJUGATES:: Proteoglycans &Proteoglycans &

glycoproteins play important roles in informationglycoproteins play important roles in informationtransfer in living organisms.transfer in living organisms.

ProteoglycansProteoglycans are enormous moleculesare enormous molecules

consisting of hyaluronate with attached coreconsisting of hyaluronate with attached coreproteins that bear numerousproteins that bear numerousglycosaminoglycans 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 peptidoglyc an peptidoglyc an, a network of polysaccharide, a network of polysaccharideand poypeptide chains.and poypeptide chains.

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Summary contd.Summary contd.--33

GlycoproteinsGlycoproteins or Glycosylated proteins mayor Glycosylated proteins may

containcontain --linked oligosacchs attached to Asnlinked oligosacchs attached to Asn

(asparagine) or O(asparagine) or O--linked oligosacchs attached tolinked oligosacchs attached to

Ser or Thr (serine or threonine) or bothSer or Thr (serine or threonine) or both

Different molecules of glycoproteins may containDifferent molecules of glycoproteins may containdifferent sequences and locations of different sequences and locations of

oligosaccharides.oligosaccharides.

Occur in cells in both soluble and membraneOccur in cells in both soluble and membrane

bound forms, and in extracellular fluidsbound forms, and in extracellular fluids



E D OTESE D OTES

The destiny of a nation depends on theThe destiny of a nation depends on the

manner in which it feeds itself.manner in which it feeds itself.

We eat to live, OT, live to eat.We eat to live, OT, live to eat.

Lower your carbohydrate consumption, butLower your carbohydrate consumption, but

balance it with the right amount of proteinbalance it with the right amount of protein

and fat.and fat.

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Lecture 3 - Carbohydrates