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CBSEClass-12Chemistry

QuickRevisionNotes

Chapter14

Biomolecules

Carbohydrates:Polyhydroxyaldehydesorpolyhydroxyketonesorcompoundson

hydrolysisgivecarbohydrates.

Classificationofcarbohydrates:

Monosaccharides

(a)Simplestcarbohydrates

(b)Itcannotbehydrolysedintosimplercompounds

(c)Examples-Glucose,mannose

Oligosaccharides

(a)Carbohydrateswhichgives2to10monosaccharideunitsonhydrolysis

(b)Examples-Sucrose,Lactose,Maltose

Polysaccharides

(a)Carbohydrateswhichonhydrolysisgivelargenumberofmonosaccharideunits.

(b)Examples-Cellulose,starch

Anomers:PairofopticalisomerswhichdifferinconfigurationonlyaroundC1atom

arecalledanomers.Examples- -D-glucopyranoseand -D-glucopyranose.

Epimers:PairofopticalisomerswhichdifferinconfigurationaroundanyotherC

atomotherthanC1atomarecalledepimers.E.g.D-glucoseandD-mannoseare

C2epimers.

Preparationofglucose(alsocalleddextrose,grapesugar):

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Fromstarch

Structureofglucose

Structureelucidationofglucose:

a)D–glucosewithHI

b)D–glucosewithHCN

c)D–glucosewithNH2OH

d)D-glucosewithFehling’sreagent

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e)D–glucosewithTollen’sreagent

f)D–glucosewithnitricacid

g)D–glucosewith(CH3CO)2OandZnCl2

h)D–glucosewithbrominewater

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i)Glucosewithphenylhydrazinetoformosazone

GlucoseandfructosegivesthesameosazonebecausethereactiontakesplaceatC1andC2

only.

OtherReactionsofGlucose(Presenceofringstructure)

GlucosedoesnotgiveSchiff’stestanddoesnotreactwithsodiumbisulphiteandNH3.

Pentaacetylglucosedoesnotreactwithhydroxylamine.Thisshowstheabsenceof–CHO

groupandhencethepresenceofringstructure.

Cyclicstructureofglucose:

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Haworthrepresentationofglucose:

Cyclicstructureoffructose:

Haworthrepresentationoffructose

Glycosidiclinkage:Theoxidelinkageformedbythelossofawatermoleculewhen

twomonosaccharidesarejoinedtogetherthroughoxygenatomiscalledglycosidic

linkage.

Sucrose(invertsugar):

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a)Sucroseisanon-reducingsugarbecausethetwomonosaccharideunitsareheldtogether

byaglycosidiclinkagebetweenC1of -glucoseandC2of -fructose.Sincethereducing

groupsofglucoseandfructoseareinvolvedinglycosidicbondformation,sucroseisanon-

reducingsugar.

b)Sucroseisdextrorotatorybutonhydrolysisitgivesdextrorotatory&laevorotatoryandthe

mixtureislaevorotatory.

HaworthProjectionofSucrose:

Maltose:

1. Maltoseiscomposedoftwoα-D-glucoseunitsinwhichC1ofoneglucose(I)islinkedtoC4

ofanotherglucoseunit(II).

2. ThefreealdehydegroupcanbeproducedatC1ofsecondglucoseinsolutionanditshows

reducingpropertiessoitisareducingsugar.

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Haworthprojectionofmaltose:

Lactose(Milksugar):Itiscomposedofβ-D-galactoseandβ-D-glucose.Thelinkageis

betweenC1ofgalactoseandC4ofglucose.Henceitisalsoareducingsugar.

Haworthprojectionoflactose:

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Starch:Itisapolymerof-glucoseandconsistsoftwocomponents—Amyloseand

Amylopectin.

Amylose:

1. Itisawatersolublecomponent

2. Itisalongunbranchedchainpolymer

3. Itcontains200–1000 -D-(+)-glucoseunitsheldby -glycosidiclinkagesinvolvingC1–

C4glycosidiclinkage

4. Itconstitutesabout15-20%ofstarch

Amylopectin

1. Itisawaterinsolublecomponent

2. Itisbranchedchainpolymer

3. ItformschainbyC1–C4glycosidiclinkagewhereasbranchingoccursbyC1–

C6glycosidiclinkage

4. Itconstitutesabout80-85%ofstarch

Cellulose:

1. Itoccursexclusivelyinplants.

2. Itisastraightchainpolysaccharidecomposedonlyof -D-glucoseunitswhicharejoined

byglycosidiclinkagebetweenC1ofoneglucoseunitandC4ofthenextglucoseunit.

Glycogen:

1. Thecarbohydratesarestoredinanimalbodyasglycogen.

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2. ItisalsoknownasanimalstarchbecauseitsstructureissimilartoAmylopectin.

3. Itispresentinliver,musclesandbrain.

4. Whenthebodyneedsglucose,enzymesbreaktheglycogendowntoglucose.

Aminoacids:

Aminoacidscontainamino(–NH2)andcarboxyl(–COOH)functionalgroups.

WhereR–Anysidechain

MostnaturallyoccurringaminoacidshaveL–Config.

Typesofaminoacids:

a).Essentialaminoacids:Theaminoacidswhichcannotbesynthesisedinthebodyand

mustbeobtainedthroughdiet,areknownasessentialaminoacids.Examples:Valine,

Leucine

b).Non-essentialaminoacids:Theaminoacids,whichcanbesynthesisedinthebody,are

knownasnon-essentialaminoacids.Examples:Glycine,Alanine

Zwitterionformofaminoacids:

1. Aminoacidsbehavelikesaltsratherthansimpleaminesorcarboxylicacids.This

behaviourisduetothepresenceofbothacidic(carboxylgroup)andbasic(aminogroup)

groupsinthesamemolecule.Inaqueoussolution,thecarboxylgroupcanloseaproton

andaminogroupcanacceptaproton,givingrisetoadipolarionknownaszwitterion.

Thisisneutralbutcontainsbothpositiveandnegativecharges.

2. Inzwitterionicform,aminoacidsshowamphotericbehaviourastheyreactbothwith

acidsandbases.

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Isoelectronicpoint:ThepHatwhichthedipolarionexistsasneutralionanddoes

notmigratetoeitherelectrodecathodeoranodeiscalledisoelectronicpoint.

Proteins:Proteinsarethepolymersof -aminoacidsandtheyareconnectedtoeach

otherbypeptidebondorpeptidelinkage.Apolypeptidewithmorethanhundred

aminoacidresidues,havingmolecularmasshigherthan10,000uiscalledaprotein.

Peptidelinkage:Peptidelinkageisanamidelinkageformedbycondensation

reactionbetween–COOHgroupofoneaminoacidand–NH2groupofanotheramino

acid.

Peptidelinkage

Primarystructureofproteins:Thesequenceofaminoacidsissaidtobetheprimary

structureofaprotein.

Secondarystructureofproteins:Itreferstotheshapeinwhichlongpolypeptide

chaincanexist.Twodifferenttypesofstructures:

–Helix:

1. ItwasgivenbyLinusPaulingin1951

2. ItexistswhenR-groupislarge.

3. RighthandedscrewwiththeNHgroupofeachaminoacidresidueH–bondedto–C=O

ofadjacentturnofthehelix.

4. Alsoknownas3.613helixsinceeachturnofthehelixhasapproximately3.6aminoacids

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anda13–memberedringisformedbyH–bonding.

5. C=OandN–Hgroupofthepeptidebondsaretranstoeachother.

6. Ramchandranangles( and )- anglewhich makeswithN–Hand anglewhich

makeswithC=O.

–pleatedsheet:

1. ItexistswhenRgroupissmall.

2. Inthisconformation,allpeptidechainsarestretchedouttonearlymaximumextension

andthenlaidsidebysidewhichareheldtogetherbyhydrogenbonds.

Tertiarystructureofproteins:Itrepresentstheoverallfoldingofthepolypeptide

chaini.e.,furtherfoldingofthe2°structure.

Typesofbondingwhichstabilizethe3°structure:

1. Disulphidebridge(-S–S-)

2. H–bonding–(C=O…H–N)

3. Saltbridge(COO–…+ )

4. Hydrophobicinteractions

5. vanderWaalsforces

Twoshapesofproteins:

Fibrousproteins

a)Whenthepolypeptidechainsrunparallelandareheldtogetherbyhydrogenand

disulphidebonds,thenfibre–likestructureisformed.

b)Theseproteinsaregenerallyinsolubleinwater

c)Examples:keratin(presentinhair,wool,silk)andmyosin(presentinmuscles),etc

Globularproteins

a)Thisstructureresultswhenthechainsofpolypeptidescoilaroundtogiveaspherical

shape.

b)Theseareusuallysolubleinwater.

c)Examples:Insulinandalbumins

Quaternarystructureofproteins:

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1. Someoftheproteinsarecomposedoftwoormorepolypeptidechainsreferredtoassub-

units.

2. Thespatialarrangementofthesesubunitswithrespecttoeachotherisknownas

quaternarystructureofproteins.

Denaturationofproteins:

1. Thelossofbiologicalactivityofproteinswhenaproteininitsnativeform,issubjectedto

physicalchangelikechangeintemperatureorchemicalchangelikechangeinpH.Thisis

calleddenaturationofprotein.

2. Example:coagulationofeggwhiteonboiling,curdlingofmilk.

Nucleoside:

1. Base+sugar

Nucleotide:

1. Base+sugar+phosphategroup

Nucleicacids(orpolynucletides):

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1. Longchainpolymersofnucleotides.

2. Nucleotidesarejoinedbyphosphodiesterlinkagebetween5’and3’Catomsofapentose

sugar.

Twotypesofnucleicacids:

DNA

1. Ithasadoublestranded -helixstructureinwhichtwostrandsarecoiledspirallyin

oppositedirections.

2. Sugarpresentis –D–2-deoxyribose

3. Bases:

i)Purinebases:Adenine(A)andGuanine(G)

ii)Pyrimidinebases:Thymine(T)andcytosine(C)

4. Itoccursmainlyinthenucleusofthecell.

5. Itisresponsiblefortransmissionforhereditycharacter.

RNA

1. Ithasasinglestranded -helixstructure.

2. Sugarpresentis –D–ribose

3. Bases:

i)Purinebases:Adenine(A)andGuanine(G)

ii)Pyrimidinebases:Uracil(U)andcytosine(C)

4. Itoccursmainlyinthecytoplasmofthecell.

5. Ithelpsinproteinsynthesis.

DoublehelixstructureofDNA:

1. Itiscomposedoftworighthandedhelicalpolynucleotidechainscoiledspirallyin

oppositedirectionsaroundthesamecentralaxis.

2. Twostrandsareanti-paralleli.e.,theirphosphodiesterlinkagerunsinopposite

directions.

3. Basesarestackedinsidethehelixinplanes tothehelicalaxis.

4. TwostrandsareheldtogetherbyH–bonds(A=T,G C).

5. Thetwostrandsarecomplementarytoeachotherbecausethehydrogenbondsare

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formedbetweenspecificpairsofbases.

6. Adenineformshydrogenbondswiththyminewhereascytosineformshydrogenbonds

withguanine.

7. Diameterofdoublehelixis2nm.

8. Doublehelixrepeatsatintervalsof3.4nm.(Onecompleteturn)

9. Totalamountofpurine(A+G)=Totalamountofpyramidine(C+T)

Vitamins:Vitaminsareorganiccompoundsrequiredinthedietinsmallamountsto

performspecificbiologicalfunctionsfornormalmaintenanceofoptimumgrowthand

healthoftheorganism.

Classificationofvitamins:Vitaminsareclassifiedintotwogroupsdependingupon

theirsolubilityinwaterorfat.

1. Watersolublevitamins

i)Thesevitaminsaresolubleinwater.

ii)Watersolublevitaminsmustbesuppliedregularlyindietbecausetheyarereadily

excretedinurineandcannotbestored(exceptvitaminB12)inourbody.

iii)Example:VitaminC,Bgroupvitamins.

2. Fatsolublevitamins

i)Thesevitaminsaresolubleinfatandoilsbutinsolubleinwater.

ii)Theyarestoredinliverandadipose(fatstoring)tissues.

iii)Example:VitaminA,D,EandK

Importantvitamins,theirsourcesandtheirdeficiencydiseases:

Nameof

vitaminsSources Deficiencydiseases

VitaminAFishliveroil,

carrots,butterandmilk

xerophthalmia

(hardeningofcorneaofeye)

Nightblindness

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VitaminB1

(Thiamine)

Yeast,milk,green

vegetablesandcereals

Beriberi

(lossofappetite,retardedgrowth)

VitaminB2

(Riboflavin)

Milk,eggwhite,liver,

kidney

Cheilosis

(fissuringatcornersofmouthandlips),digestive

disordersandburningsensationoftheskin.

VitaminB6

(Pyridoxine)

Yeast,milk,eggyolk,

cerealsandgramsConvulsions

VitaminB12 Meat,fish,eggandcurdPerniciousanaemia

(RBCdeficientinhaemoglobin)

VitaminC

(Ascorbic

acid)

Citrusfruits,amlaand

greenleafyvegetables

Scurvy

(bleedinggums)

VitaminDExposuretosunlight,fish

andeggyolk

Rickets

(bonedeformitiesinchildren)and

osteomalacia

(softbonesandjointpaininadults)

VitaminEVegetableoilslikewheat

germoil,sunfloweroil,etc.

IncreasedfragilityofRBCsand

muscularweakness

VitaminK Greenleafyvegetables Increasedbloodclottingtime