cbse class-12 chemistry quick revision notes
TRANSCRIPT
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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