CBSE Class–12 Subject Chemistry NCERT Exemplar Solutions ...

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1 / 12 CBSE Class–12 Subject Chemistry NCERT Exemplar Solutions Chapter 14 Biomolecules Multiple Choice Questions (Type-I) 1. Glycogen is a branched chain polymer of α-D-glucose units in which chain is formed by C 1 —C 4 glycosidic linkage whereas branching occurs by the formation of C 1 -C 6 glycosidic linkage. Structure of glycogen is similar to __________. (i) Amylose (ii) Amylopectin (iii) Cellulose (iv) Glucose Ans. (ii) Amylopectin Explanation: Polysaccharides contain a large number of monosaccharide units joined together by glycosidic linkages. These are the most commonly encountered carbohydrates in nature. Amylopectin is insoluble in water and constitutes about 80-85% of starch. It is a branched chain polymer of alpha-D-glucose units in which chain is formed by C 1 -C 4 glycosidic linkage whereas branching occurs by C 1 -C 6 glycosidic linkage. 2. Which of the following polymer is stored in the liver of animals? (i) Amylose (ii) Cellulose (iii) Amylopectin (iv) Glycogen Ans. (iv) Glycogen Explanation: The carbohydrates are stored in animal body as glycogen. It is also known as animal starch because its structure is similar to amylopectin and is rather more highly CAREER POINT www.ecareerpoint.com

Transcript of CBSE Class–12 Subject Chemistry NCERT Exemplar Solutions ...

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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

NCERTExemplarSolutions

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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