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CBSEClass–12SubjectChemistry

NCERTExemplarSolutions

Chapter14

Biomolecules

MultipleChoiceQuestions(Type-I)

1.Glycogenisabranchedchainpolymerofα-D-glucoseunitsinwhichchainisformed

byC1—C4glycosidiclinkagewhereasbranchingoccursbytheformationofC1-C6

glycosidiclinkage.Structureofglycogenissimilarto__________.

(i)Amylose

(ii)Amylopectin

(iii)Cellulose

(iv)Glucose

Ans.(ii)Amylopectin

Explanation:Polysaccharidescontainalargenumberofmonosaccharideunitsjoined

togetherbyglycosidiclinkages.Thesearethemostcommonlyencounteredcarbohydratesin

nature.Amylopectinisinsolubleinwaterandconstitutesabout80-85%ofstarch.Itisa

branchedchainpolymerofalpha-D-glucoseunitsinwhichchainisformedbyC1-C4

glycosidiclinkagewhereasbranchingoccursbyC1-C6glycosidiclinkage.

2.Whichofthefollowingpolymerisstoredintheliverofanimals?

(i)Amylose

(ii)Cellulose

(iii)Amylopectin

(iv)Glycogen

Ans.(iv)Glycogen

Explanation:Thecarbohydratesarestoredinanimalbodyasglycogen.Itisalsoknownas

animalstarchbecauseitsstructureissimilartoamylopectinandisrathermorehighly

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branched.Itispresentinliver,musclesandbrain.

3.Sucrose(canesugar)isadisaccharide.Onemoleculeofsucroseonhydrolysisgives

_________.

(i)2moleculesofglucose

(ii)2moleculesofglucose+1moleculeoffructose

(iii)1moleculeofglucose+1moleculeoffructose

(iv)2moleculesoffructose

Ans.(iii)1moleculeofglucose+1moleculeoffructose

Explanation:Oneofthecommondisaccharidesissucrosewhichonhydrolysisgives

equimolarmixtureofD-(+)-glucoseandD-(-)fructose.

4.Whichofthefollowingpairsrepresentsanomers?

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Ans.(iii)

Explanation:Thetwocyclichemiacetalformsofglucosedifferonlyintheconfigurationof

thehydroxylgroupatCl,calledanomericcarbon(thealdehydecarbonbeforecyclisation).

Suchisomers,i.e.,alpha-formandbeta-form,arecalledanomers.

5.Proteinsarefoundtohavetwodifferenttypesofsecondarystructuresviz.α-helix

andβ-pleatedsheetstructure.α-helixstructureofproteinisstabilisedby:

(i)Peptidebonds

(ii)vanderWaalsforces

(iii)Hydrogenbonds

(iv)Dipole-dipoleinteractions

Ans.(iii)Hydrogenbonds

Explanation:α-helixandβ-pleatedsheetstructure:Thesestructuresariseduetothe

regularfoldingofthebackboneofthepolypeptidechainduetohydrogenbondingbetween

>C—Oand—NH—groupofthepeptidebond.

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-Helixisoneofthemostcommonwaysinwhichapolypeptidechainformsallpossible

hydrogenbondbytwistingintoaright-handedscrew(helix)withthe-NHgroupofeach

aminoacidresiduehydrogenbondedtothe ofanadjacentturnofthehelix.

6.Indisaccharides,ifthereducinggroupsofmonosaccharidesi.e.aldehydicorketonic

groupsarebonded,thesearenon-reducingsugars.Whichofthefollowingdisaccharide

isanon-reducingsugar?

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Ans.(ii)

Explanation:Oneofthecommondisaccharidesissucrosewhichonhydrolysisgives

equimolarmixtureofD-(+)-glucoseandD-(-)fructose.Thesetwomonosaccharidesareheld

togetherbyaglycosidiclinkagebetweenClof -glucoseandC2ofbeta-fructose.

Sincethereducinggroupsofglucoseandfructoseareinvolvedinglycosidicbondformation,

sucroseisanon-reducingsugar.

7.Whichofthefollowingacidsisavitamin?

(i)Asparticacid

(ii)Ascorbicacid

(iii)Adipicacid

(iv)Saccharicacid

Ans.(ii)Ascorbicacid

Explanation:VitaminCisalsoknownasAscorbicacid.

8.Dinucleotideisobtainedbyjoiningtwonucleotidestogetherbyphosphodiester

linkage.Betweenwhichcarbonatomsofpentosesugarsofnucleotidesarethese

linkagespresent?

(i)5′and3′

(ii)1′and5′

(iii)5′and5′

(iv)3′and3′

Ans.(i)5′and3′

Explanation:Nucleotidesarejoinedtogetherbyphosphodiesterlinkagebetween5’and3’

carbonatomsofthepentosesugar.

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9.Nucleicacidsarethepolymersof______________.

(i)Nucleosides

(ii)Nucleotides

(iii)Bases

(iv)Sugars

Ans.(ii)Nucleotides

Explanation:Nucleicacidsarelongchainpolymersofnucleotides,sotheyarealsocalled

polynucleotides.

10.Whichofthefollowingstatementsisnottrueaboutglucose?

(i)Itisanaldohexose.

(ii)OnheatingwithHIitformsn-hexane.

(iii)Itispresentinfuranoseform.

(iv)Itdoesnotgive2,4-DNPtest.

Ans.(iii)

Explanation:Fructoseispresentinfuranoseform.

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11.Eachpolypeptideinaproteinhasaminoacidslinkedwitheachotherinaspecific

sequence.Thissequenceofaminoacidsissaidtobe____________.

(i)primarystructureofproteins.

(ii)secondarystructureofproteins.

(iii)tertiarystructureofproteins.

(iv)quaternarystructureofproteins.

Ans.(i)primarystructureofproteins.

Explanation:Sequenceofaminoacidsissaidtobeprimarystructureofproteins.

12.DNAandRNAcontainfourbaseseach.Whichofthefollowingbasesisnotpresent

inRNA?

(i)Adenine

(ii)Uracil

(iii)Thymine

(iv)Cytosine

Ans.(iii)Thymine

Explanation:DNAcontainsfourbasesviz.adenine(A),guanine(G),cytosine(C)and

thymine(T).RNAalsocontainsfourbases;thefirstthreebasesaresameasinDNAbutthe

fourthoneisuracil(U).

13.WhichofthefollowingBgroupvitaminscanbestoredinourbody?

(i)VitaminB1

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(ii)VitaminB2

(iii)VitaminB6

(iv)VitaminB12

Ans.(iv)VitaminB12

Explanation:Watersolublevitaminsmustbesuppliedregularlyindietbecausetheyare

readilyexcretedinurineandcannotbestored(exceptvitaminB12)inourbody.

14.WhichofthefollowingbasesisnotpresentinDNA?

(i)Adenine

(ii)Thymine

(iii)Cytosine

(iv)Uracil

Ans.(iv)Uracil

Explanation:UracilispresentinRNAbutnotinDNA.

15.Threecyclicstructuresofmonosaccharidesaregivenbelowwhichoftheseare

anomers.

(i)IandII

(ii)IIandIII

(iii)IandIII

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(iv)IIIisanomerofIandII

Ans.(i)IandII

Explanation:Thisbehaviorcouldnotbeexplainedbytheopenchainstructure(I)for

glucose.Itwasproposedthatoneofthe—OHgroupsmayaddtothe—CHOgroupandform

acyclichemiacetalstructure.Itwasfoundthatglucoseformsasix-memberedringinwhich

—OHatC-5isinvolvedinringformation.Thisexplainstheabsenceof—CHOgroupandalso

existenceofglucoseintwoformsasshownbelow.

16.Whichofthefollowingreactionsofglucosecanbeexplainedonlybyitscyclic

structure?

(i)Glucoseformspentaacetate.

(ii)Glucosereactswithhydroxylaminetoformanoxime.

(iii)Pentaacetateofglucosedoesnotreactwithhydroxylamine.

(iv)Glucoseisoxidisedbynitricacidtogluconicacid.

Ans.(iii)Pentaacetateofglucosedoesnotreactwithhydroxylamine.

Explanation:Thepentaacetateofglucosedoesnotreactwithhydroxylamineindicatingthe

absenceoffree—CHOgroup.

17.OpticalrotationsofsomecompoundsalongwiththeirstructuresaregivenBelow.

WhichofthemhaveDconfiguration.

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(i)I,II,III

(ii)II,III

(iii)I,II

(iv)III

Ans.(i)I,II,III

Explanation:Allthosecompoundswhichcanbechemicallycorrelatedto(+)isomerof

glyceraldehydearesaidtohaveD-configurationwhereasthosewhichcanbecorrelatedto(-)

isomerofglyceraldehydearesaidtohaveL-configuration.

18.Structureofadisaccharideformedbyglucoseandfructoseisgivenbelow.Identify

anomericcarbonatomsinmonosaccharideunits.

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(i)‘a’carbonofglucoseand‘a’carbonoffructose.

(ii)‘a’carbonofglucoseand‘e’carbonoffructose.

(iii)‘a’carbonofglucoseand‘b’carbonoffructose.

(iv)‘f’carbonofglucoseand‘f’carbonoffructose.

Ans.(iii)‘a’carbonofglucoseand‘b’carbonoffructose.

Explanation:TwomonosaccharidesareheldtogetherbyaglycosidiclinkagebetweenClof

-glucoseandC2of -fructose.

19.Threestructuresaregivenbelowinwhichtwoglucoseunitsarelinked.Whichof

theselinkagesbetweenglucoseunitsarebetweenC1andC4andwhichlinkagesare

betweenC1andC6?

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(i)(A)isbetweenC1andC4,(B)and(C)arebetweenC1andC6

(ii)(A)and(B)arebetweenC1andC4,(C)isbetweenC1andC6

(iii)(A)and(C)arebetweenC1andC4,(B)isbetweenC1andC6

(iv)(A)and(C)arebetweenC1andC6,(B)isbetweenC1andC4

Ans.(iii)(A)and(C)arebetweenC1andC4,(B)isbetweenC1andC6

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CBSEClass–12SubjectChemistry

NCERTExemplarSolutions

Chapter14

Biomolecules

MultipleChoiceQuestions(Type-II)

Note:Inthefollowingquestionstwoormoreoptionsmaybecorrect.

20.Carbohydratesareclassifiedonthebasisoftheirbehaviouronhydrolysisandalso

asreducingornon-reducingsugar.Sucroseisa__________.

(i)monosaccharide

(ii)disaccharide

(iii)reducingsugar

(iv)non-reducingsugar

Ans.(ii),(iv)

Explanation:Oneofthecommondisaccharidesissucrosewhichonhydrolysisgives

equimolarmixtureofD-(+)-glucoseandD-(-)fructose.Thesetwomonosaccharidesareheld

togetherbyaglycosidiclinkagebetweenClof -glucoseandC2of -fructose.Sincethe

reducinggroupsofglucoseandfructoseareinvolvedinglycosidicbondformation,sucroseis

anon-reducingsugar.

21.Proteinscanbeclassifiedintotwotypesonthebasisoftheirmolecularshapei.e.,

fibrousproteinsandglobularproteins.Examplesofglobularproteinsare:

(i)Insulin

(ii)Keratin

(iii)Albumin

(iv)Myosin

Ans.(i),(iii)

Explanation:Globularproteins:Thisstructureresultswhenthechainsofpolypeptidescoil

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aroundtogiveasphericalshape.Theseareusuallysolubleinwater.Insulinandalbumins

arethecommonexamplesofglobularproteins.

22.Whichofthefollowingcarbohydratesarebranchedpolymerofglucose?

(i)Amylose

(ii)Amylopectin

(iii)Cellulose

(iv)Glycogen

Ans.(ii),(iv)

Explanation:Amylopectinisinsolubleinwaterandconstitutesabout80-85%ofstarch.Itis

abranchedchainpolymerof–D-glucoseunitsinwhichchainisformedbyCl-C4glycosidic

linkagewhereasbranchingoccursbyC1-C6glycosidiclinkage.Glycogen:Thecarbohydrates

arestoredinanimalbodyasglycogen.Itisalsoknownasanimalstarchbecauseitsstructure

issimilartoamylopectinandisrathermorehighlybranched.

23.Aminoacidsareclassifiedasacidic,basicorneutraldependingupontherelative

numberofaminoandcarboxylgroupsintheirmolecule.Whichofthefollowingare

acidic?

(i)

(ii)

(iii)H2N—CH2—CH2—CH2—COOH

(iv)

Ans.(ii),(iv)

Explanation:Aminoacidsareclassifiedasacidic,basicorneutraldependinguponthe

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relativenumberofaminoandcarboxylgroupsintheirmolecule.Equalnumberofamino

andcarboxylgroupsmakesitneutral;morenumberofaminothancarboxylgroupsmakesit

basicandmorecarboxylgroupascomparedtoaminogroupsmakesitacidic.

24.Lysine, is_______________.

(i)α-Aminoacid

(ii)Basicaminoacid

(iii)Aminoacidsynthesisedinbody

(iv)β-Aminoacid

Ans.(i),(ii)

25.Whichofthefollowingmonosaccharidesarepresentasfivememberedcyclic

structure(furanosestructure)?

(i)Ribose

(ii)Glucose

(iii)Fructose

(iv)Galactose

Ans.(i),(iii)

Explanation:Fructose:Italsoexistsintwocyclicformswhichareobtainedbytheaddition

of—OHatC5tothegroup.Thering,thusformedisafive-memberedringandisnamedas

furanosewithanalogytothecompoundfuran.Furanisafive-memberedcycliccompound

withoneoxygenandfourcarbonatoms.

26.Infibrousproteins,polypeptidechainsareheldtogetherby___________.

(i)vanderWaalsforces

(ii)disulphidelinkage

(iii)electrostaticforcesofattraction

(iv)hydrogenbonds

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Ans.(i),(ii)

Explanation:Infibrousproteins,mainforceswhichstabilizestructuresofproteinsare

disulphidelinkagesandvanderWaals.

27.Whichofthefollowingarepurinebases?

(i)Guanine

(ii)Adenine

(iii)Thymine

(iv)Uracil

Ans.(i),(ii)

28.Whichofthefollowingtermsarecorrectaboutenzyme?

(i)Proteins

(ii)Dinucleotides

(iii)Nucleicacids

(iv)Biocatalysts

Ans.(i),(iv)

Explanation:Lifeispossibleduetothecoordinationofvariouschemicalreactioninliving

organisms.Thisoccurswiththehelpofcertainbiocatalystscalledenzymes.Almostallthe

enzymesareglobularProtein.

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CBSEClass–12SubjectChemistry

NCERTExemplarSolutions

Chapter14

Biomolecules

ShortAnswerType

29.Namethesugarpresentinmilk.Howmanymonosaccharideunitsarepresentinit?

Whataresucholigosaccharidescalled?

Ans.Lactoseiscommonlyknownasmilksugarsincethisdisaccharideisfoundinmilk.Itis

composedofβ-D-galactoseandβ-D-glucose.ThelinkageisbetweenC1ofgalactoseandC4of

glucose.

30.Howdoyouexplainthepresenceofallthesixcarbonatomsinglucoseinastraight

chain?

Ans.OnprolongedheatingwithHI,glucosegivesn-hexane.

31.Innucleosideabaseisattachedat1′positionofsugarmoiety.Nucleotideisformed

bylinkingofphosphoricacidunittothesugarunitofnucleoside.Atwhichpositionof

sugarunitisthephosphoricacidlinkedinanucleosidetogiveanucleotide?

Ans.Phosphoricacidislinkedat5′-positionofsugarmoietyofnucleosidetogivea

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nucleotide.

32.Namethelinkageconnectingmonosaccharideunitsinpolysaccharides.

Ans.Glycosidiclinkage.

33.Underwhatconditionsglucoseisconvertedtogluconicandsaccharicacid?

Ans.Glucoseisconvertedtogluconicacidbybrominewaterandtosaccharicacidbyconc.

HNO3.

34.Monosaccharidescontaincarbonylgrouphenceareclassified,asaldoseorketose.

Thenumberofcarbonatomspresentinthemonosaccharidemoleculearealso

consideredforclassification.Inwhichclassofmonosaccharidewillyouplacefructose?

Ans.Fructoseisanimportantketohexose.Itisobtainedalongwithglucosebythehydrolysis

ofdisaccharide,sucrose.FructosealsohasthemolecularformulaC6H12O6andonthebasis

ofitsreactionsitwasfoundtocontainaketonicfunctionalgroupatcarbonnumber2and

sixcarbonsinstraightchainasinthecaseofglucose.

35.Theletters‘D’or‘L’beforethenameofastereoisomerofacompoundindicatethe

correlationofconfigurationofthatparticularstereoisomer.Thisreferstotheir

relationwithoneoftheisomersofglyceraldehyde.Predictwhetherthefollowing

compoundhas‘D’or‘L’configuration.

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Ans.Theletters‘D’or‘L’beforethenameofanycompoundindicatetherelative

configurationofaparticularstereoisomer.Thisreferstotheirrelationwithaparticular

isomerofglyceraldehydes.

D’beforethenameofglucoserepresentstheconfigurationwhereas‘(+)’represents

dextrorotatorynatureofthemolecule.Itmayberememberedthat‘D’and‘L’haveno

relationwiththeopticalactivityofthecompound.Forassigningtheconfigurationof

monosaccharides,itisthelowestasymmetriccarbonatomwhichiscompared.Thegiven

compoundhasL-configuration.

36.Aldopentosesnamedasriboseand2-deoxyribosearefoundinnucleicacids.Whatis

theirrelativeconfiguration?

Ans.configurationassignedisO.Thus,roboseisβ-D-riboseDeoxyriboseisβ-D-2-

deoxyribose.

37.Whichsugariscalledinvertsugar?Whyisitcalledso?

Ans.Sucroseisdextrorotatorybutafterhydrolysisgivesdextrorotatoryglucoseand

laevorotatoryfructose.Sincethelaevorotationoffructose ismorethan

dextrorotationofglucose ,themixtureislaevorotatory.Thus,hydrolysisofsucrose

bringsaboutachangeinthesignofrotation,fromdextro(+)tolaevo(-)andtheproductis

namedasinvertsugar.

38.Aminoacidscanbeclassifiedasα-,β-,γ-,δ-andsoondependingupontherelative

positionofaminogroupwithrespecttocarboxylgroup.Whichtypeofaminoacids

formpolypetidechaininproteins?

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Ans. -aminoacidsformpolypeptidechaininproteins.

39.α-Helixisasecondarystructureofproteinsformedbytwistingofpolypeptidechain

intorighthandedscrewlikestructures.Whichtypeofinteractionsare

responsibleformakingtheα-helixstructurestable?

Ans.In -helix,apolypeptidechainisstabilizedbytheformationofhydrogenbonds

between—NH—groupofaminoacidsinoneturnwiththe>C—Ogroupsofaminoacids

belongingtoadjacentturn.

40.Someenzymesarenamedafterthereaction,wheretheyareused.Whatnameis

giventotheclassofenzymeswhichcatalysetheoxidationofonesubstratewith

simultaneousreductionofanothersubstrate.

Ans.Oxidoreductaseisclassofenzymeswhichcatalysetheoxidationofonesubstratewith

simultaneousreductionofanothersubstrate.

41.Duringcurdlingofmilk,whathappenstosugarpresentinit?

Ans.Whenmilkiscurdeled,itssugargetoxidizetoformlacticacid.

42.Howdoyouexplainthepresenceoffive—OHgroupsinglucosemolecule?

Ans.Acetylationofglucosewithaceticanhydridegivesglucosepentaacetatewhichconfirms

thepresenceoffive—OHgroups.Sinceitexistsasastablecompound,five—OHgroups

shouldbeattachedtodifferentcarbonatoms.

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43.Whydoescompound(A)givenbelownotformanoxime?

Ans.Glucosepentaacetate(structureA)doesn’thaveafree—OHgroupatC1andsocan’tbe

convertedtotheopenchainformtogive—CHOgroupandhencedoesn’tformtheoxime.

44.WhymustvitaminCbesuppliedregularlyindiet?

Ans.VitaminCaresolubleinwater.Watersolublevitaminsmustbesuppliedregularlyin

dietbecausetheyarereadilyexcretedinurineandcannotbestoredinourbody.

45.Sucroseisdextrorotatorybutthemixtureobtainedafterhydrolysisis

laevorotatory.Explain.

Ans.Sucroseisdextrorotatorybutafterhydrolysisgivesdextrorotatoryglucoseand

laevorotatoryfructose.Sincethelaevorotationoffructose ismorethan

dextrorotationofglucose ,themixtureislaevorotatory.

46.Aminoacidsbehavelikesaltsratherthansimpleaminesorcarboxylicacids.

Explain.

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Ans.Aminoacidsbehavelikesaltsratherthansimpleaminesorcarboxylicacids.This

behaviourisduetothepresenceofbothacidic(carboxylgroup)andbasic(aminogroup)

groupsinthesamemolecule.Inaqueoussolution,thecarboxylgroupcanloseaprotonand

aminogroupcanacceptaproton,givingrisetoadipolarionknownaszwitterion.

47.Structuresofglycineandalaninearegivenbelow.Showthepeptidelinkagein

glycylalanine.

Ans.Inglycylalanine,carboxylgroupofglycinecombineswiththeaminogroupofalanine.

48.Proteinfoundinabiologicalsystemwithauniquethree-dimensionalstructureand

biologicalactivityiscalledanativeprotein.Whenaproteininitsnativeform,is

subjectedtoaphysicalchangelikechangeintemperatureorachemicalchangelike,

changeinpH,denaturationofproteintakesplace.Explainthecause.

Ans.Proteinfoundinabiologicalsystemwithauniquethree-dimensionalstructureand

biologicalactivityiscalledanativeprotein.Whenaproteininitsnativeform,issubjectedto

physicalchangelikechangeintemperatureorchemicalchangelikechangeinpH,the

hydrogenbondsaredisturbed.Duetothis,Globulesunfoldandhelixgetuncoiledand

proteinlosesitsbiologicalactivity.Thisiscalleddenaturationofprotein.

49.Activationenergyfortheacidcatalysedhydrolysisofsucroseis6.22kJmol-1,while

theactivationenergyisonly2.15kJmol–1whenhydrolysisiscatalysedbytheenzyme

sucrase.Explain.

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Ans.Enzymesareneededonlyinsmallquantitiesfortheprogressofareaction.Similarto

theactionofchemicalcatalysts,enzymesaresaidtoreducethemagnitudeofactivation

energy.Forexample,activationenergyforacidhydrolysisofsucroseis6.22kJmol-1,while

theactivationenergyisonly2.15kJmol-1whenhydrolysedbytheenzyme,sucrase.

50.Howdoyouexplainthepresenceofanaldehydicgroupinaglucosemolecule?

Ans.Glucosegetsoxidisedtosixcarboncarboxylicacid(gluconicacid)onreactionwitha

mildoxidisingagentlikebrominewater.Thisindicatesthatthecarbonylgroupispresentas

analdehydicgroup.

51.Whichmoietiesofnucleosidesareinvolvedintheformationofphosphodiester

linkagespresentindinucleotides?Whatdoestheworddiesterinthenameoflinkage

indicate?Whichacidisinvolvedintheformationofthislinkage?

Ans.Whennucleosideislinkedtophosphoricacidat5-positionofsugarmoiety,itformsa

nucleotide.Nucleotidesarejoinedtogetherbyphosphodiesterlinkbetween5’and3’carbon

atomsofthepentosesugar.

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Phosphericacidisinvolvedintheformationofthislinkage.

52.Whatareglycosidiclinkages?Inwhichtypeofbiomoleculesaretheypresent?

Ans.Thetwomonosaccharidesarejoinedtogetherbyanoxidelinkageformedbythelossof

awatermolecule.Suchalinkagebetweentwomonosaccharidesareheldtogetherbya

glycosidiclinkagebetweenC1of -glucoseandC2ofβ-fructose.Sincethereducinggroups

ofglucoseandfructoseareinvolvedinglycosidicbondformation,betweentwo

monosaccharideunitsthroughoxygenatomiscalledglycosidiclinkage.

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53.Whichmonosaccharideunitsarepresentinstarch,celluloseandglucoseandwhich

linkageslinktheseunits?

Ans.Instarchandglycogen,glycosidic -linkageispresent.Celluloseisastraightchain

polysaccharidecomposedonlyofβ-D-glucoseunitswhicharejoinedbyglycosidiclinkage

betweenC1ofoneglucoseunitandC4ofthenextglucoseunit.

54.Howdoenzymeshelpasubstratetobeattackedbythereagenteffectively?

Ans.Enzymesarehighlyspecific.Theyreactwithsubstratemoleculeandformintermediate

complex.Theyreducethemagnitudeofactivationenergy.

55.DescribethetermD-andL-configurationusedforaminoacidswithexamples.

Ans.Aminoacidexistsbothin‘D’and‘L’forms.Mostnaturallyoccurringaminoacidshave

L-configuration.L-Aminoacidsarerepresentedbywritingthe—NH2grouponlefthandside

andD-aminoacidsarerepresentedbywritingthe—NH2grouponrighthandside.

56.Howwillyoudistinguish1°and2°hydroxylgroupspresentinglucose?Explainwith

reactions.

Ans.Onoxidationwithnitricacid,glucoseaswellasgluconicacidbothyieldadicarboxylic

acid,saccharicacid.Thisindicatesthepresenceofaprimaryalcoholic(—OH)groupin

glucose.

Acetylationofglucosewithaceticanhydridegivesglucosepentaacetatewhichconfirmsthe

presenceoffive—OHgroups.Sinceitexistsasastablecompound,five—OHgroupsshould

beattachedtodifferentcarbonatoms.

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57.Coagulationofeggwhiteonboilingisanexampleofdenaturationofprotein.

Explainitintermsofstructuralchanges.

Ans.Duringdenaturation2and3structuresaredestroyedbut structureremainsintact.

Thecoagulationofeggwhiteonboilingisacommonexampleofdenaturation.

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CBSEClass–12SubjectChemistry

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Chapter14

Biomolecules

MatchingType

Note:MatchtheitemsofColumnIandColumnIIinthefollowingquestions.Morethan

oneoptioninColumnIImaymatchwiththeitemsgiveninColumnI.

58.MatchthevitaminsgiveninColumnIwiththedeficiencydiseasetheycausegivenin

ColumnII.

ColumnI(Vitamins) ColumnII(Diseases)

(i)VitaminA (a)Perniciousanaemia

(ii)VitaminB1 (b)Increasedbloodclottingtime

(iii)VitaminB12 (c)Xerophthalmia

(iv)VitaminC (d)Rickets

(v)VitaminD (e)Muscularweakness

(vi)VitaminE (f)Nightblindness

(vii)VitaminK

(g)BeriBeri

(h)Bleedinggums

(i)Osteomalacia

Ans.(i)-(c)(ii)-(g)(iii)-(a)(iv)-(h)(v)-(d)(vi)-(e)(vii)-(b)

Explanation:

(i) Xerophthalmia(hardeningofcorneaofeye)nightblindness.

(ii) Beriberi(lossofappetite,retardedgrowth).

(iii) Perniciousanaemia(RBCdeficientinhaemoglobin).

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(iv) Scurvy(bleedinggums).

(v)Rickets(bonedeformitiesinchildren)andosteomalacia(softbonesand

jointpaininadults)

(vi) IncreasedfragilityofRBCsandmuscularweakness.

(vii) Increasedbloodclottingtime.

59.MatchthefollowingenzymesgiveninColumnIwiththereactionstheycatalyse

giveninColumnII.

ColumnI(Enzymes) ColumnII(Reactions)

(i)Invertase (a)DecompositionofureaintoNH3andCO2

(ii)Maltase (b)Conversionofglucoseintoethylalcohol

(iii)Pepsin (c)Hydrolysisofmaltoseintoglucose

(iv)Urease (d)Hydrolysisofcanesugar

(v)Zymase (e)Hydrolysisofproteinsintopeptides

Ans.(i)-(d)(ii)-(c)(iii)-(e)(iv)-(a)(v)-(b)

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CBSEClass–12SubjectChemistry

NCERTExemplarSolutions

Chapter14

Biomolecules

AssertionandReasonType

Note:Inthefollowingquestionsastatementofassertionfollowedbyastatementof

reasonisgiven.Choosethecorrectansweroutofthefollowingchoices.

(i)Assertionandreasonbotharecorrectstatementsandreasonexplainstheassertion.

(ii)Bothassertionandreasonarewrongstatements.

(iii)Assertioniscorrectstatementandreasoniswrongstatement.

(iv)Assertioniswrongstatementandreasoniscorrectstatement.

(v)Assertionandreasonbotharecorrectstatementsbutreasondoesnotexplainassertion.

60.Assertion:D(+)–Glucoseisdextrorotatoryinnature.

Reason:‘D’representsitsdextrorotatorynature.

Ans.(iii)Assertioniscorrectstatementandreasoniswrongstatement.

Explanation:GlucoseiscorrectlynamedasD(+)-glucose.‘D’beforethenameofglucose

representstheconfigurationwhereas‘(+)’representsdextrorotatorynatureofthemolecule.

Theletters‘D’or‘L’beforethenameofanycompoundindicatetherelativeconfigurationof

aparticularstereoisomer.

61.Assertion:VitaminDcanbestoredinourbody.

Reason:VitaminDisfatsolublevitamin.

Ans.(i)Assertionandreasonbotharecorrectstatementsandreasonexplainstheassertion.

Explanation:Fatsolublevitaminsaresolubleinfatandoilsbutinsolubleinwater.Theycan

bestoredinliverandadipose(fatstoring)tissues.

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62.Assertion:β-glycosidiclinkageispresentinmaltose,

Reason:MaltoseiscomposedoftwoglucoseunitsinwhichC–1ofoneglucoseunitislinked

toC–4ofanotherglucoseunit.

Ans.(iv)Assertioniswrongstatementandreasoniscorrectstatement.

Explanation:

Maltoseiscomposedoftwo -D-glucoseunitsinwhichC1ofoneglucose(I)islinkedtoC4

ofanotherglucoseunit(II).

63.Assertion:Allnaturallyoccurringα-aminoacidsexceptglycineareopticallyactive.

Reason:MostnaturallyoccurringaminoacidshaveL-configuration.

Ans.(v)Assertionandreasonbotharecorrectstatementsbutreasondoesnotexplain

assertion.

Explanation:Exceptglycine,allothernaturallyoccurring -aminoacidsareoptically

active,sincethe -carbonatomisasymmetric.Theseexistbothin‘D’and‘L’forms.Most

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naturallyoccurringaminoacidshaveL-configuration.L-Aminoacidsarerepresentedby

writingthe—NH2grouponlefthandside.

64.Assertion:Deoxyribose,C5H10O4isnotacarbohydrate.

Reason:CarbohydratesarehydratesofcarbonsocompoundswhichfollowCx(H2O)y

formulaarecarbohydrates.

Ans.(ii)Bothassertionandreasonarewrongstatements

Explanation:CompletehydrolysisofDNA(orRNA)yieldsapentosesugar,phosphoricacid

andnitrogencontaininghetero-cycliccompounds(calledbases).InDNAmolecules,thesugar

moietyisβ-D-2-deoxyribose.

65.Assertion:Glycinemustbetakenthroughdiet.

Reason:Itisanessentialaminoacid.

Ans.(ii)Bothassertionandreasonarewrongstatements

Explanation:Theaminoacids,whichcanbesynthesisedinthebody,areknownasnon-

essentialaminoacids.Glycineisanexampleofnon-essentialaminoacid.

66.Assertion:Inpresenceofenzyme,substratemoleculecanbeattackedbythereagent

effectively.

Reason:Activesitesofenzymesholdthesubstratemoleculeinasuitableposition.

Ans.(i)Assertionandreasonbotharecorrectstatementsandreasonexplainstheassertion.

Explanation:Inpresenceofenzyme,substratemoleculecanbeattackedbythereagent

effectivelybecauseactivesitesofenzymesholdthesubstratemoleculeinasuitableposition.

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CBSEClass–12SubjectChemistry

NCERTExemplarSolutions

Chapter14

Biomolecules

LongAnswerType

67.WritethereactionsofD-glucosewhichcan’tbeexplainedbyitsopen-chain

structure.Howcancyclicstructureofglucoseexplainthesereactions?

Ans.Followingreactionsandfactscouldnotbeexplainedbyopenchainstructureof

glucose.

Despitehavingthealdehydegroup,glucosedoesnotgive2,4-DNPtest,Schiff’stestand

itdoesnotformthehydrogensulphiteadditionproductwithNaHSO3.

Thepentaacetateofglucosedoesnotreactwithhydroxylamineindicatingtheabsence

offree—CHOgroup.

Itwasproposedthatoneofthe—OHgroupsmayaddtothe—CHOgroupandformacyclic

hemiacetalstructure.Itwasfoundthatglucoseformsasix-memberedringinwhich—OHat

C-5isinvolvedinringformation.

68.OnthebasisofwhichevidencesD-glucosewasassignedthefollowingstructure?

Ans.Glucoseisanaldohexoseandisalsoknownasdextrose.Itisthemonomerofmanyof

thelargercarbohydrates,namelystarch,cellulose.Itisprobablythemostabundantorganic

compoundonearth.Itwasassignedthestructuregivenbelowonthebasisofthefollowing

evidences:

(i)ItsmolecularformulawasfoundtobeC6H12O6.

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(ii)OnprolongedheatingwithHI,itformsn-hexane,suggestingthatallthesixcarbonatoms

arelinkedinastraightchain.Glucosereactswithhydroxylaminetoformanoximeandadds

amoleculeofhydrogencyanidetogivecyanohydrins.Thesereactionsconfirmthepresence

ofacarbonylgroup(>C=O)inglucose.Glucosegetsoxidisedtosixcarboncarboxylicacid

(gluconicacid)onreactionwithamildoxidisingagentlikebrominewater.Thisindicates

thatthecarbonylgroupispresentasanaldehydicgroup.

69.Carbohydratesareessentialforlifeinbothplantsandanimals.Namethe

carbohydratesthatareusedasstoragemoleculesinplantsandanimals,alsonamethe

carbohydratewhichispresentinwoodorinthefibreofcottoncloth.

Ans.Starchisthemainstoragepolysaccharideofplants.Itisthemostimportantdietary

sourceforhumanbeings.Highcontentofstarchisfoundincereals.Celluloseoccurs

exclusivelyinplantsanditisthemostabundantorganicsubstanceinplantkingdom.Cell

wallofbacteriaandplantsismadeupofcellulose.Webuildfurniture,etc.fromcellulosein

theformofwoodandclotheourselveswithcelluloseintheformofcottonfibre.

70.Explainthetermsprimaryandsecondarystructureofproteins.Whatisthe

differencebetweenα-helixandβ-pleatedsheetstructureofproteins?

Ans.Primarystructureofproteins:Proteinsmayhaveoneormorepolypeptidechains.

Eachpolypeptideinaproteinhasaminoacidslinkedwitheachotherinaspecificsequence

anditisthissequenceofaminoacidsthatissaidtobetheprimarystructureofthatprotein.

Anychangeinthisprimarystructurei.e.,thesequenceofaminoacidscreatesadifferent

protein.

SecondaryStructureofProteins:Thesecondarystructureofproteinreferstotheshapein

whichalongpolypeptidechain.Thesecondarycanexist.Theyarefoundtoexistintwo

differenttypesofstructuresviz. -helixandβ-pleatedsheetstructure.Thesestructures

ariseduetotheregularfoldingofthebackboneofthepolypeptidechainduetohydrogen

bondingbetweencarbonylgroupand—NH—groupsofthepeptidebond. -Helixisoneof

themostcommonwaysinwhichapolypeptidechainformsallpossiblehydrogenbondsby

twistingintoarighthandedscrew(helix)withthecarbonyland—Nhgroupofeachamino

acidresiduehydrogenbondedtothe(>C=O)ofanadjacentturnofthehelix.

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Inβ-structureallpeptidechainsarestretchedouttonearlymaximumextensionandthen

laidsidebysidewhichareheldtogetherbyintermolecularhydrogenbonds.

71.WritethestructuresoffragmentsproducedoncompletehydrolysisofDNA.How

aretheylinkedinDNAmolecule?Drawadiagramtoshowpairingofnucleotidebases

indoublehelixofDNA.

Ans.CompletehydrolysisofDNA(orRNA)yieldsapentosesugar,phosphoricacidand

nitrogencontainingheterocycliccompounds(calledbases).InDNAmolecules,thesugar

moietyisβ-D-2-deoxyribose.

Twonucleicacidchainsarewoundabouteachotherandheldtogetherbyhydrogenbonds

betweenpairsofbases.Thetwostrandsarecomplementarytoeachotherbecausethe

hydrogenbondsareformedbetweenspecificpairsofbases.

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