Biomolecules Part

7/23/2019 Biomolecules Part

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Biomolecules 5

CHAPTER CONTENTS

11.1 Carbohydrates 11.7 Lipids

11.2 Monosaccharides 11.8 Energy cycle or Metabolism

11.3 Disaccharides 11.9 Digestion of food

11.4 Polysaccharide (Starch and

cellulose)11.10 Vitamins

11.5 Proteins and amino acids 11.11 ormones

11.6 !ucleic acids

Assignment (Basic and Advance Level)Answer Sheet of Assignment

261

Chapter

""

Chapter

""



6 Biomolecules

All living bodies are composed of several lifeless substances which are present in

their cells in a very complex but highly organised form. These are called biomolecules.

Some common examples are carbohydrates, proteins, enzymes, nucleic acids, lipids,

amino acids, fats etc :

Livi! "r!ai#$s Or!a# Ti##%e# Ce&&# Or!ae&&e# 'i"$"&e(%&e#.

11.1 Carbohydrates.

#he carbohydrates are naturally occurring organic substances$ #hey are present in both

plants and animals$ #he dry mass of plants is composed of %& to '& of the polymeric

carbohydrate cellulose$ Carbohydrates are formed in the plants by photosynthesis from carbon

dioide and *ater$

++lChlorophyl

Light++ )( nOOCHOnHnCO n + → +

,nimals do not synthesise carbohydrates but depends on plants for their supply$

(1) Defination : -Carbohydrates are de.ned as a class of compounds that include polyhydric

aldehydes or polyhydric /etones and large polymeric compounds that can be bro/en do*n

(hydrolysed) into polyhydric aldehydes or /etones$0

Carbohydrates contain OC => and OH− groups$ , carbonyl compound reacts *ith analcohol to form hemiacetal$

emiacetal

,lcohol

,ldehyde

1

1

1OH

RO

H

CRRHOO

H

CR

′

−− → ′+=−

2n carbohydrates3 the carbonyl group combine *ith an alcoholic group of the same

molecules to form an internal hemiacetal thus the correct de.nation of carbohydrates is as

follo*s

-, polyhydroy compound that has an aldehydic or a /etonic functional group either free oras hemiacetal or acetal$0

262

H OH

C

CHOH1

CHOH1

CHOH1

CH1

CH+OH

1

,n internalhemiacetal

O

H O

C

CHOH1

CHOH1

CHOH1

CHOH1

CH+OH

1

4lucose (C5H

"+O

5)



Biomolecules 7

2n general3 carbohydrates are *hite solids3 sparingly soluble in organic sol6ents and (ecept

certain polysaccharides) are soluble in *ater$ Many carbohydrates of lo* molecular masses ha6e

a s*eet taste$(2) omenclat!re : #he name of simpler carbohydrates end is 7ose$ Carbohydrate *ith an

aldehydic structure are /no*n as aldoses and those *ith /etonic structure as /etoses$ #he

number of carbon atom in the molecule is indicated by 4ree/ pre.$N%$)er "* (ar)" at"$# i

the $"&e(%&e

A&+"#e ,et"#e

8 ,ldotriose 9etotriose: ,ldotetrose 9etotetrose% ,ldopentose 9etopentose5 ,ldoheose 9etoheose; ,ldoheptose 9etoheptose

(3) Classification : #he complete class.cation of carbohydrates may be depicted in short in

the follo*ing chart <

11." #onosaccharides.

#hese are the simplest one unit non=hydrolysable sugars$ #hey ha6e the general formula

nnn OHC + *here n 6aries from 8 to > carbon atoms$ ,bout +& monosaccharides occur in nature$

#he simplest are trioses (n?8)

#riose858 OHC @

hyde4lyceralde+

1

1

OHCH

OHCH

OCH

−−

=−

@

cetoneDihydroya+

+

1

1

OHCH

OC

OHCH

=

#he most important naturally occurring monosaccharides are pentoses and heoses$ ,

common pentose is ribose and t*o common heoses are glucose and fructose$

Ecept /etotriose Adihydroyacetone3 all aldose and /etoses Amonosaccharides contain

asymmetric carbon atoms and are optically acti6e$ !umber of isomers depand upon the numberof asymmetric carbon atom in the molecules of monosaccharide and is deri6ed by the formula + n

*here n is the number of asymmetric carbon atoms in the molecules$

Carbohydrates

Sugars !on=sugars(Polysaccharides

)

omopoly 7saccharides

eteropoly 7saccharides

Monosaccharides ligosaccharides

,ldoses 9etoses

Disaccharides

#risaccharides

#etrasaccharides

$$ $$ $$



8 Biomolecules

N%$)er "* (ar)" at"$# N". "* a#-$$etri( (ar)"

at"$#

N". "* i#"$er#

#rioses 8 CH+OHCHOHCHOCH+OHCOCH+OH

"7

+7

#etroses :CH+OH(CHOH)+CHO

CH+OHCHOHCOCH+OH

+

"

:

+

Pentoses %CH+OH(CHOH)8CHO

CH+OH(CHOH)+COCH+OH

8

+

'

:

eoses 5CH+OH(CHOH):CHO

CH+OH(CHOH)8COCH+OH

:

8

"5

'

C&a## "&e(%&ar *"r$%&a Str%(t%ra& *"r$%&a E/a$p&e#

A&+"#e#

,ldotrioses C8H5O8 CH+OHCHOHCHO 4lyceraldehyde

,ldotetroses C:H'O: CH+OH(CHOH)+CHO Erythrose3 #hreose,ldopentoses C%H"&O% CH+OH(CHOH)8CHO ,rabinose3 ibose3 Fylose3 Lyose

,ldoheoses C5H"+O5 CH+OH(CHOH):CHO 4lucose3 4alactose3 Mannose3

,llose3 #alose3 4ulose3 2dose3 etc$

,et"#e#

9etotrioses C8H5O8 CH+OHCO.CH+OH Dihydroyacetone

9etotetroses C:H'O: CH+OH.CO.CHOH.CH+OH Erythrulose

9etopentoses C%H"&O% CH+OH$CO$(CHOH)+CH+OH ibulose3 Fylulose

9etoheoses C5H"+O5 CH+OH.CO(CHOH)8CH+OH Gructose3 Sorbose3 #angatose3

Psicose

(1) D and L$designation : By ("veti" a molecule is assigned D=con.guration if the 7OH

group attached to the carbon adHacent to the 7CH+OH group (last chiral carbon) is on the righthand side irrespecti6e of the position of other groups$ n the other hand3 the molecule is

assigned L=con.guration if the 7OH group attached to the carbon adHacent to the 7CH+OH group is

on the left$

o*e6er3 it may be noted that D= and L= do not represent detrorotatory or lae6orotatory$

#he optical acti6ity of the molecule is represented by (I) and (7) *hich represent the direction of

rotation of plane polariJed light *hether detrorotatory or lae6orotatory$

(2) Config!ration : Con.guration of Monosaccharides

(i) Aldotriose

(ii) Aldotetrose

So it has four isomers3 i.e., D3 L=Erythrose and D, L=#hreose$

CHO.CHOHCH+OH

CHO

H – C – OH1

1CH

+OH

D=4lyceraldehyde

isomers (+)" ? +

CHO

OH – C – H1

1CH

+OH

L=4lyceraldehyde

CHO.CHOH.CHOH.CH+OH

CHO

H – C – OH1

1

CH+OHD=Erythrose

H – C – OH1

CHO

HO – C – H1

1

CH+OHD=#hreose

H – C – OH1

isomers (+)+?:

L-Erythrose L- #hreose



Biomolecules 9

(iii) Aldopentose : CHO.CHOH.CHOH.CHOH.CH+OH3 isomers (+)8 ? '

So aldopentoses has eight isomers3 i.e.3 D= and L=ibose3 D= and L=,rabinose3 D= and L=

Fylose and D, L=Lyose(i6) Aldohexose : CHO.(CHOH):CH+OH, isomers (+): ? "5

(3) %l!cose& C'1"'& Aldo$he*ose : 4lucose is /no*n as +e/tr"#e because it occurs in nature

as the optically acti6e detrorotatory isomer$ 2t is also called grape sugar as it is found in most

s*eet fruits especially grapes$ 2t is present in honey also$ 2t is essential constituent of human

blood$ #he blood normally contains 5% to ""& mg of glucose per "&& mL (hence named Blood

sugar)$ 2n combined form3 it occurs in cane sugar and polysaccharides such as starch and

cellulose$ 2t is also present in 6arious glycosides li/e a$-!+a&i and #a&i(i.

(i) Preparation(a) Laboratory method

Gructose5"+5

4lucose5"+5+

(Sucrose)sugarCane

""++"+ OHCOHCOHOHC H

+ → ++

!ote < HCl (dil$) is used for hydrolysis$ 4lucose being much less soluble in alcohol

than fructose separates out by crystallising on cooling$

(b) Manufacture 2t is obtained on a large scale by the hydrolysis of starch (corn starch or

potato starch) *ith dilute sulphuric acid or hydrochloric acid$

4lucose5"+5+

Starch%"&5 )( OHnCOnHOHC

Hn → +

+

, thin paste of starch is boiled *ith dilute acid till the hydrolysis is complete$ #he ecess of acid is neutralised *ith chal/ (calcium carbonate) and the .ltrate containing glucose is

D=Erythrose

CHO

H – C – OH1

1CH

+OH

D=ibose

H – C – OH1

H – C – OH1

CHO

OH – C – H1

1CH

+OH

D=,rabinose

H – C – OH1

H – C – OH1

D=#hreose

CHO

H – C – OH1

1CH

+OH

D=Fylose

HO – C – H1

H – C – OH1

CHO

HO – C – H1

1CH

+OH

D=Lyose

HO – C – H1

H – C – OH1

D=ibose

CHO

H – C – OH1

1CH

+OH

D=,llose

H – C – OH1

H – C – OH1

H – C – OH

1

CHO

HO – C – H1

1CH

+OH

D=,ltrose

H – C – OH1

H – C – OH1

H – C – OH

1

D=,rabinose

CHO

H – C – OH1

1CH

+OH

D=4lucose

HO – C – H1

H – C – OH1

H – C – OH1

CHO

HO – C – H1

1CH

+OH

D=Mannose

HO – C – H1

H – C – OH1

H – C – OH1

D=Fylose

CHO

H – C – OH1

1CH

+OH

D=4ulose

H – C – OH1

HO – C – H1

H – C – OH

1

CHO

HO – C – H1

1CH

+OH

D=2dose

H – C – OH1

HO – C – H1

H – C – OH

1

D=Lyose

CHO

H – C – OH1

1CH

+OH

D=4lactose

HO – C – H1

HO – C – H1

H – C – OH

1

CHO

HO – C – H1

1CH

+OH

D=#alose

HO – C – H1

HO – C – H1

H – C – OH

1



10 Biomolecules decolourised *ith animal charcoal$ #he solution is concentrated and e6aporated under reducedpressure$ 4lucose is obtained in crystalline form$

(ii) Physical properties 2t is a colourless crystalline solid3 melts at Co":5 $ 2t is readilysoluble in *ater$ Grom aKueous solution3 it separates as a crystalline monohydrate

)$( +5"+5 OHOHC *hich melts at Co'5 $ 2t is sparingly soluble in alcohol but insoluble in ether$ 2t

is less s*eet (three=fourth) than cane sugar$ 2t is optically acti6e and the ordinary naturallyoccuring form is (I) glucose or detro form$ 2t sho*s $%tar"tati".

(iii) hemical properties 4lucose is a polyhydroy aldehyde i.e. aldoheose$ 2t has .6e 7OH groups and one aldehydic group$ 2t sho*s characteristics of hydroyl and aldehydic group$2mportant chemical reaction of the glucose are the follo*ing <

(a) !lcoholic reaction (Reaction due to –OH grou")

• eaction *ith acid chlorides and acid anhydride

HCl

OOCCHCH

CHOOCCH

CHO

COClCH

OHCH

CHOH

CHO

#nCl %

1

)(

1

%

1

)(

1

acetate=penta4lucose8+

:8chloride,cetyl

8

4lucose+

:+ + → +

#his sho*s that a molecule of glucose contains % 7 OH groups$

• eaction *ith $Cl%

HCl$OCl

ClCH

CHCl

CHO

$Cl

OHCH

CHOH

CHO

%%1

)(

1

%1

)(

1

8

chloride)=penta(4lucose

osechlorogluc=Penta+

:%

4lucose+

: ++ → +

• eaction *ith metallic hydroides <

OHOHCaOOHCOHCaOHOHOHC +glucosateCalcium

%""5hydroideCalcium4lucose

%""5 LLLLLL + → +

!ote < 4lucose beha6es as a *ea/ acid$ 2nstead of +)(OHCa *e can ta/e other

metallic hydroide li/e +++ )(3)(3)( OHCuOH%r OH&a etc to form glucosate *hich is soluble in

*ater$

• Gormation of glycosides < OHOCHOHCOCHHOHOHC HCl+

glucosideMethyl=andN=8%""58%""5 L + → +

#his reaction sho*s the presence of ring structure in glucose$

H OCH8

(CHOH)8

1

C1

CH1CH

+OH

α=Methylglucoside

O

CH'O H

(CHOH)8

1

C1

CH1CH

+OH

β=Methylglucoside

O



Biomolecules 11

(b) Reaction of carbonyl grou" (!ldehydic grou")

• eduction <Sorbitol

+:+

4lucose

:+ )(+)(+

OHCHCHOHOHCHHCHOCHOHOHCH

OH

Hg)a → +

−

n prolonged heating *ith concentrated H* and red phosphorus at Co""& 3 glucose forms a

miture of +=iodoheane and n=heane$

• idation

eaction *ith Gehling solution <

ppt$)(red+

acid4luconic:+

4lucose:+ )(+)( OCuCOOHCHOHOHCHCuOCHOCHOHOHCH + → + $

eaction *ith #ollenOs reagent <

ppt$Qor blac/(Mirror)

:++:+ +)()( !gCOOHCHOHOHCHO !gCHOCHOHOHCH + → +$

eaction *ith Bromine *ater <acid4luconic

:+R

4lucose:+ )(Q)( ++ COOHCHOHOHCHOCHOCHOHOHCH OH&r → + $

eaction *ith !itric acid < OHCOOHCHOHCOOHOCHOCHOHOHCHC

H)O

C+

)(acidSaccharic:

)(4lucose:+

5

8

5

)(Q8)( + → + $

• eaction *ith HC <OH

C)

CHCHOHOHCHHC)CHOCHOHOHCHncyanohydri4lucose:+:+ )()( → + $

• eaction *ith hydroyl amine

OH)OHCHCHOHOHCHOH)HCHOCHOHOHCH +oime4lucose

:++:+ )()( +=→+ $

• eaction *ith Phenyl hydraJine (Gischers mechanism) < Then *armed *ith ecess of phenyl hydraJine3 glucose .rst forms phenylhydraJone by condensation *ith 7 CHO group$

#he adHacent 7 CHOH group is then oidised by a second molecule of phenyl hydraJine$

#he resulting carbonyl compounds reacts *ith a third molecule of phenyl hydraJine to yield

glucosaJone$

CHO1CHOH1

(CHOH)'

1CH

+OH

4lucose

+ H+HC

5H

%Phenyl hydraJine

Tarm

CH1CHOH1

(CHOH)'

1CH

+OH

4lucose phenylhydraJone

HC5H

%

CH

1C O1

(CHOH)'

1CH

+OH

9eto compound of4lucose phenyl

hydraJone

HC5H

%

+ C5H

%H

+ I H

8

CH

1CHOH1

(CHOH)'

1CH

+OH

HC5H

%

+ H+HC

5H

%

CH1C

1(CHOH)

'1CH

+OH

4lucosaJone

HC5H

%

HC5

H%

I H+

O

CH1C O

1(CHOH)

'1CH

+OH

HC5H

%

+ H+HC

5H

%



12 Biomolecules

(c) Micellaneou reaction

• Germentation < +Ethanol

%+4lucose

5"+5 ++ COOHHCOHC #yma(e+ →

• Dehydration < Then heated strongly or *hen treated *ith *arn concentrated sulphuric

acid3 glucose is dehydrated to gi6e a blac/ mass (sugar carbon)$

• eaction *ith al/alies < Then *armed *ith concentrated al/ali3 glucose .rst turns yello*@

then bro*n and .nally gi6es a resinous mass$

, dilute solution of glucose3 *hen *armed *ith dilute solution of al/ali3 some glucose is

con6erted into fructose and mannose$ !!&%("#e and !$a"#e are epi$er#$

• ,ction of concentrated hydrochloric acid

OHHCOOHCOOHCHCOCHCHOHC HClConc+

acidLae6ulic++8

$5"+5 ++ →

n treatment *ith conc$ 3HCl glucose can also form hydroymethyl furfural$

#his on acid treatment gi6es lae6ulic acid

(i6) "ses

(a) 2n the preser6ation of fruits and preparation of Hams and Hellies$(b) 2n the preparation of confectionary and as a s*eetening agent$

(c) ,s a food for patients3 in6alids and children$

CH O1

H C OH

4lucose …

CH OH11

C OH

Enol …

CH+OH

1

C O

Gructose

…

HO CH11

HO C

Enol …

CH O1

HO C H

Mannose …

C

HO – C – H1

1CH

+OH

D(+) Mannose

HO – C – H1

H – C – OH

1

H – C – OH1

O H

C

H – C – OH1

1CH

+OH

D(+) 4lucose

HO – C – H1

H – C – OH

1

H – C – OH1

O H

Epimers

C5H

"+O

5CH CH11 11

HOCH+ C C CHO

Oydroymethyl

furfural

+ 8H+O



Biomolecules 13

(d) 2n the form of calcium glucosate as medicine in treatment of calcium de.ciency$

(e) ,s a reducing agent in sil6ering of mirrors$

(f) ,s a ra* material for alcoholic preparations$(g) 2n industrial preparation of 6itamin=C$

(h) 2n the processing of tobacco$

(i) ,s an intra6enous inHection to the patients *ith lo*er glucose content in blood$

(6) Test of glucose

(a) Then heated in a dry test tube3 it melts3 turns bro*n and .nally blac/3 gi6ing a

characteristic smell of burnt sugar$

(b) Then *armed *ith a little conc$ :+%OH 3 it lea6es a charred residue of carbon$

(c) Then it is boiled *ith dilute )aOH solution3 it .rst turns yello* and then bro*n$

(d) Molich tet < #his is a general test for carbohydrates$ , drop or t*o of alcoholic

solution of α=naphthol is added to +mL of glucose solution$ " mL of concentrated :+%OH is

added carefully along the sides of the test tube$ #he formation of a 6iolet ring3 at the Hunction of

t*o liKuids con.rms the presence of a carbohydrate$

(e) %il/er mirror tet < , miture of glucose and ammonical sil6er nitrate is *armed in a test

tube$ ,ppearance of sil6er mirror on the inner *alls con.rms glucose$

(f) 0ehling olution tet < , little glucose is *armed *ith GehlingOs solution$ , red

precipitate of cuprous oide is formed$

(g) Oa1one formation < 4lucose on heating *ith ecess of phenyl hydraJine in acetic acid

gi6es a yello* crystalline compound3 m$pt$ Co+&% $

(6i) Structure of glucose < #he structure of glucose has been established as follo*s

(a) O"en chain tructure < 2t is based on the follo*ing points <

• Elemental analysis and molecular mass determination sho* that the molecular formula of

glucose is 5"+5 OHC $

• 4lucose on complete reduction *ith H* and red phosphorus .nally gi6es n-heane$ #his

indicates that it contains a straight chain of si carbon atoms$

• 2t reacts *ith acetic anhydride and forms penta=acetate deri6ati6e$ #his sho*s the

presence of .6e hydroyl groups each lin/ed to a separate carbon atom as the molecule is

stable$

• 4lucose combines *ith hydroyl amine to form a monoime$ 2t also combines *ith one

mole of HC) to form a cyanohydrin$ #hese reactions indicate the presence of a carbonyl group3OC => 3 in the molecule$

• Mild oidation of glucose *ith bromine *ater gi6es gluconic acid$ #his sho*s the presence

of an aldehyde group$

n the basis of abo6e obser6ations3 the follo*ing open chain structure can be *ritten for

glucose$

#here are four asymmetric carbon atoms mar/ed by asteris/s (U) in the molecule$ #his

representation is incomplete3 because a de.nite con.guration to these asymmetric centres has

H C C C C C C O1

1U1

U1

U1

U1 1

1111

H H H H H

OH OH OH OH OH H



14 Biomolecules not been assigned$ #he con.guration of D=glucose *as pro6ed by E$i& i#(her$ #he structure of

D=glucose as elucidated by Emil Gischer is3

Evi+e(e a!ai#t "pe (hai #tr%(t%re #he open chain formula of glucose accountsfor most of the reactions satisfactorily but fails to eplain the follo*ing

E6en though an aldehyde group is present3 the glucose does not react *ith 8)aH%O and

8)H $

4lucose does not gi6e the SchiOs test for aldehydes$ 4lucose does not react *ith 4rignard reagents$ 4lucose penta=acetate does not react *ith hydroyl=amine$

#*o isomeric methyl glucosides (α and β) are obtained by heating glucose *ith methyl

alcohol in presence of dry HCl gas$

4lucose eists in t*o stereoisomeric forms (α and β)$ α= glucose *ith speci.c rotationo""&+ is obtained by crystalliJing glucose from alcohol or acetic acid solution3 *hereas β=glucose

*ith speci.c rotation o;$">+ is obtained by crystalliJing glucose from pyridine solution$

,n aKueous solution of glucose sho*s $%tar"tati" i.e., its speci.c rotation gradually

decreases from o""&+ to o%$%++ in case of α=glucose and increases from o;$">+ to I o%$%+ in

case of β=glucose$,ll these obser6ation indicate that free aldehydic group is not present in the molecule$(b) Cyclic tructure of glucoe < D=glucose eists in t*o optically acti6e forms /no*n as α=D=

glucose and β=D=glucose$

α=D=glucose has speci.c rotation of o""&+ and β=D=glucose has speci.c rotation of o;$">+ $

#he t*o isomers are intercon6ertible in aKueous solution$ #he eKuilibrium rotation is o%++ $ #heeKuilibrium miture has 85 α=glucose3 5: β=glucose$ 4lucose forms a stable cyclic hemiacetal(according to Gischer) bet*een CHO− group and the OH− group of the .fth carbon atom inpyranose structure$ 2n this process .rst carbon atom becomes asymmetric gi6ing t*o isomers (2)and (22) *hich dier only in the con.guration of the .rst asymmetric carbon$

"C

H – C – OH1

1

CH+OH

D-4lucose

HO – C – H1

H – C – OH1

H – C – OH1

H O

+

8

:

%

5

"C

CHOH1

1CH

+OH

D-4lucose

CHOH1

CHOH1

CHOH1

H O

+

8

:

%

5

"

C

CHOH1

1CH

+OH

α -D-4lucose (2)

CHOH1

CHOH1

CH1

H OH

+

8

:

%

5

O

"

C

CHOH1

1CH

+OH

β -D-4lucose (22)

CHOH1

CHOH1

CH1

HO H

+

8

:

%

5

O

QαD ? I %+$%o

α=4lucose85

QαD ? I ""&o

pen chain form&$&+

QαD ? I ">$;o

β=4lucose5:



Biomolecules 15

Carbon=" in both con.guration (2) and (22) is called an anomeric carbon atom$ Due to

anomeric carbon3 glucose eists in t*o forms$ Both the forms ha6e dierent physical properties

and are called anomers$

#he ring structure eplains all the reactions of glucose$ #he obHections against the open

chain structure of glucose ha6e also been satisfactory eplained3 e$g$3

• α= and β=glucose on treatment *ith OHCH8 in presence of dry HCl gas forms α= and β=

methyl glucosides respecti6ely$

• N" rea(ti" ith #$3 a+ #a$S%3 #he glucose ring is not 6ery stable$ 2t is easilybro/en up by #tr"! rea!et# li/e HC3 H+OH and C5H%HH+3 etc$3 to gi6e the intermediate

aldehyde form3 *hich reacts *ith them Hust li/e an aldehyde$

But *ea/ reagents li/e H8 and aH%O8 are unable to open the chain and cannot react *ith

it$ #his eplains the inability of glucose to form aldehyde ammonia and bisulphite compound$

• t e/p&ai# $%tar"tati" rdinary glucose is α=glucose3 *ith a fresh aKueous solution

has speci.c rotation3 $""&Q oD +α n /eeping the solution for some time@ α=glucose slo*ly

changes into an eKuilibrium miutre of α=glucose (85) and β=glucose (5:) and the miture has

speci.c rotation I %+$%o$

Similarly a fresh aKueous solution of β=glucose ha6ing speci.c rotation3o

D ;$">Q +α 3 on/eeping (standing) gradually changes into the same eKuilibrium miutre (ha6ing3 speci.c rotation

H – C – OH1

1CH

+OH

α -D=4lucose (2)

HO – C – H1

H – C – OH1

H – C – OH

H – C1

O + CH8OH

(Dry HCl gas)

H – C – OH1

1CH

+OH

α -D=Methyl glucoside

HO – C – H1

H – C – OH1

H – C – OCH8

H – C1

O

H – C – OH1

1CH

+OH

β -D=4lucose (22)

HO – C – H1

H – C – OH1

HO – C – H

H – C1

O + CH8OH

(Dry HCl gas)

H – C – OH1

1CH

+OH

β -D=Methyl glucoside

HO – C – H1

H – C – OH1

CH'O – C – H

H – C1

O



16 Biomolecules

)$;$%+ o+ So an aKueous solution of glucose sho*s a physical property3 /no*n as $%tar"tati"3

i$e$3 a change in the 6alue of speci.c rotation (muta?change@ rotation ? speci.c rotation) is

called $%tar"tati".

• eth"+# *"r +eter$ii! the #ie "* ri!# Gischer and #ollenOs proposed that the

ring or the internal hemiacetal is formed bet*een "C and :

C $ 2t means the ring is %ra t-pe

or %=membered ring@ this is called %ra"#e #tr%(%tre

o*e6er according to a*orth and irst the ring is formed bet*een "C and %

C $ 2t means

the ring is P-ra t-pe or 5=membered ring3 this is called P-ra"#e #tr%(t%re.

#he t*o forms of D=glucose are also sho*n by Ha"rth proHection formula *hich are gi6en

belo*@

#he abo6e proHection formulae sho* that the si membered ring is planar but actually thering has a chain structure similar to cycloheane$

2n a*orth formula all the OH groups on the right in GischerOs formula are directed belo* the

plane of the ring *hile those on the left go abo6e the plane$ #he terminal OHCH + proHects

abo6e the plane of the ring$(4) +r!ctose, fr!it s!gar C 'H 1"O ', -etohe*ose : 2t is present in abundance in fruits and hence is

called *r%it #%!ar. 2t is also present in cane sugar and honey along*ith glucose in combinedform$ #he polysaccharide i%&i is a polymer of fructose an gi6es only fructose on hydrolysis$Since naturally occurring fructose is lae6orotatory3 it is also /no*n as &aev%&"#e$

(i) Preparation

(a) Hydrolyi of cane ugar Gructose=D

5"+54lucose=D

5"+5Tarm

(dil$)+

sugarCane""++"+

:+ OHCOHCOHOHC %OH+ → +

#he solution ha6ing eKual molecules of D=glucose and D=fructose is termed ivert #%!arand the process is /no*n a# iver#i"$

!ote < #he ecess of sulphuric acid is neutralised by adding mil/ of lime$ , little

more of lime is added *hich con6erts both glucose and fructose into calcium glucosate and

calcium fructose respecti6ely$

CH CH|| ||

CH CH

O"

+%

: 8

Guran

HC CH|| ||

HC CH

O"

+5

% 8

Pyran

CH+

:

CH+OH

OHOHOH

H

H

OH

HH

H

O

"

+8

:

%

5

α -D glucose

CH+OH

HOHOH

OH

H

OH

HH

H

O

"

+8

:

%

5

β -D glucose



Biomolecules 17

8Gructose

5"+5+fructoseCalcium

%""5 CaCOOHCCOCaOHOOHC + → +−−

(b) Hydrolyi of *nulin 2ith dilute ul"huric acid Gructose

5"+5(dil$)+2nulin

%"&5:+)( OHnCOnHOHC %OHn → +

(ii) Properties #he anhydrous fructose is a colourless crystalline compounds$ 2t melts at

$"&+ Co 2t is soluble in *ater but insoluble in benJene and ether$ 2t is less soluble in *ater than

glucose$ 2t is the s*eetestU of all sugars and its solution is lae6orotatory$ Li/e glucose3 it also

sho*s $%tar"tati".

Gructose is a pentahydroy /etone and its open=chain and closed=chain structures can be

represented as <

(5) Comarison between gl!cose and fr!ctose

Pr"pert- &%("#e r%(t"#eMolecular formula C5H"+O5 C5H"+O5

!ature Polyhydroy aldehyde$ Polyhydroy /etone

Melting point ":5oC "&+oC

ptical acti6ity of natural form Detrorotatory Lae6orotatory

Tith ethyl alcohol ,lmost insoluble More soluble

idation

(a) Tith bromine *ater

(b) Tith nitric acid

4luconic acid

Saccharic acid (4lucaric acid)

!o reaction

Miture of glycollic acid3 tartaric acid

and trihydroy glutaric acid

eduction Sorbitol Miture of sorbitol and mannitol

Calcium hydroide Gorms calcium glucosate3 soluble in

*ater

Gorms calcium fructosate3 insoluble in

*ater

MolischOs reagent Gorms a 6iolet ring Gorms a 6iolet ring

GehlingOs solution 4i6es red precipitate 4i6es red precipitate

#ollenOs reagent Gorms sil6er mirror Gorms sil6er mirror

Phenyl hydraJine Gorms osaJone Gorms osaJone

esorcinol I HCl (dil$)

(Seli6anoOs test)

!o colouration 4i6es red or bro*n colour or

precipitate

Greshly prepared ammonium

molybdate sol$ I fe* drops of

acetic acid (Pi"# te#t)$

Light blue colour Bluish green colour on heating

,lcoholic α=naphthol I HCl

(conc$) (%r*%ra& te#t)

!o colouration , purple colour (6iolet) on boiling

C O

HO – C – H1

1CH

+OH

D-0ructoeQα

D ? 7 >+o

1

H – C – OH

H – C – OH1

CH+OH

1

or

C O

(CHOH)8

1

1

CH+OH

1

CH+OH

C

HO – C – H1

1CH

+

α - D- Gructose

QαD ? 7 +"o

1H – C – OH

H – C – OH1

HOH+C

O

OH

C

HO – C – H1

1CH

+

β - D- Gructose

QαD ? 7 "88o

1H – C – OH

H – C – OH1

CH+OH

O

OH



18 Biomolecules

!ote < Gructose gi6es reactions similar to glucose$ #he dierence in properties is due

to the fact that it contains a /etonic group *hile glucose contains an aldehydic group$

(6) /nterconversions

(i) hain &engthening of Aldoses '(illiani)*ischer synthesis+ #he con6ersion of an

aldose to the net higher member in6ol6es the follo*ing steps <

(a) Gormation of a cyanohydrin$

(b) ydrolysis of 7 C to 7 COOH forming aldonic acid$

(c) Con6ersion of aldonic acid into lactone by heating$

(d) #he lactone is .nally reduced *ith sodium amalgam or sodium borohydride to gi6e the

higher aldose$

(ii) hain Shortening of Aldoses 'u- !egradation+

(a) ,n aldose can be con6erted to the net lo*er member by R% :e!ra+ati". 2t in6ol6est*o steps<

• idation of the aldose to aldonic acid by using bromine *ater$

• #he aldonic acid is treated *ith 8CaCO to gi6e the calcium salt *hich is then oidised by

GentonOs reagent ( +++OH ferric sulphate) to form the net lo*er aldose$

(b) &y 3ohl method < 2t in6ol6es the follo*ing steps

• Gormation of oime *ith hydroyl amine$

• eating of oime *ith acetic anhydride undergoes dehydration into cyano compound3

*hereas the hydroyl groups get acetylated$

• #he acetyl deri6ati6e is *armed *ith ammonical sil6er nitrate *hich remo6es the acetyl

group by hydrolysis and eliminates a molecule of HC$

CHO1

(CHOH)8

1

CH+OH

,rabinose(,ldopentose)

HC

C1

CHOH1

(CHOH)8

1

CH+OH

H+O4H+

&a(OH)+

CHOH1

(CHOH)8

1

CH+OH

COOH1

4luconic acid

heat

–H+O CHOH

1

1

CH+OH

CHOH1

CHOH

O C –1

CH1

γ =Lactone

Oa – Hg

in acidsolution

O C – H1

(CHOH)8

1

CH+OH

CHOH1

4lucose(,ldoheose)

&r +

H+O

,ldoheose(D=4lucose)

CHO1

(CHOH)8

1CH

+OH

CHOH1

COOH1

(CHOH)8

1CH

+OH

CHOH1

,ldonic acid

Ca- alt

H+O+I0e8I

CHO1

(CHOH)8

1CH

+OH

,ldopentose(D=,rabinose)

H+OH

4lucose(,ldoheose)

CH O1

(CHOH)8

1

CH+OH

CHOH1

CH OH1

(CHOH)8

1

CH+OH

CHOH1

ime

!gOH

*arm(CH

8CO)

+O

C1

(CHO.COCH8)

8

1

CH+O.COCH

'

CHO.COCH'

1

C1

(CHOH)8

1

CH+OH

CHO H1 – HC

,ldopentose

(CHOH)8

1

CH+OH

CHO1



Biomolecules 19

(iii) onversion of an Aldose to the isomeric (etose #hree steps are in6ol6ed <

(a) #reatment of aldose *ith ecess of phenyl hydraJine to form osaJone$

(b) ydrolysis of osaJone *ith dil$ HCl to form osone$

(c) eduction of osone *ith Jinc and acetic acid to form /etose$

(i6) onversion of a (etose to the isomeric Aldose #*o steps are in6ol6ed3

(a) eduction of a /etose *ith )iH R+ to form polyhydric alcohol$

(b) idation *ith GentonOs reagent to form aldose$

11.0 Disaccharides.

#he disaccharides yield on hydrolysis t*o monosaccharides$ #hose disaccharides *hich

yield t*o heoses on hydrolysis ha6e a general formula $""++"+ OHC #he heoses obtained on

hydrolysis may be same or dierent$

Gructose5"+5

4lucose5"+5

Sucrose""++"+

+ OHCOHCOHCH

OH+ →

+

Lactose+

→ H

OH+

4lucose I 4alactose

Maltose+

→ H

OH+

4lucose I 4lucose

#he hydrolysis is done by dilute acids or enJymes$ #he enJymes *hich bring hydrolysis of

sucrose3 lactose and maltose are in/ertae, lactae and maltae, respecti6ely$ ut of the three

disacchrides3 sucrose (cane=sugar) is the most important as it is an essential constituent of our

diet$

C5H

%HH

+

(56ce)

4lucose

CHO1

(CHOH)8

1

CH+OH

CHOH1

HCHC5H

%1

(CHOH)8

1

CH+OH

CHC5H

%1

saJone

7H+O4H+

(–7C5H

%HH

+)

CO1

(CHOH)8

1CH

+OH

sone

HCO

1

7H

#nRCH8COOH

Gructose

CH+OH

1

(CHOH)8

1

CH+OH

CO1

H+ 4i

Gructose

CH+OH

1

(CHOH)8

1

CH+OH

CO1

CH+OH

1

(CHOH)8

1

CH+OH

CHOH1

QO

H+O

+ + 0e8I

4lucose

CHO

1

(CHOH)8

1

CH+OH

CHOH1



20 Biomolecules

2n disaccharides3 the t*o monosaccharides are Hoined together by glycoside lin/age$ ,

glycoside bond is formed *hen hydroy group of the hemiacetal carbon of one monosaccharide

condenses *ith a hydroy group of another monosaccharide gi6ing 7 7 bond$(1) S!crose& Cane$s!gar C 1"H ""O 112 : 2t is our common table sugar$ 2t is obtained from sugar

cane and sugarbeets$ 2t is actually found in all photosynthetic plants$

(i) Properties 2t is a colourless3 odourless3 crystalline compound$ 2t melts at "'% 7 "'5oC$

2t is 6ery soluble in *ater3 slightly soluble in alcohol and insoluble in ether$ 2t is detrorotatory but

does not sho* $%tar"tati". 2t is a non=reducing sugar as it does not reduce #ollenOs or

GehlingOs reagent$ Sucrose3 on heating slo*ly and carefully3 melts and then if allo*ed to cool3 it

solidi.es to pale yello* glassy mass called WBarley sugarO$ Then heated to +&& oC, it loses *ater

to form bro*n amorphous mass called Caramel. n strong heating3 it chars to almost pure

carbon gi6ing smell of burnt sugar$ 2t is composed of α=D=glucopyranose unit and a β=D=

fructofuranose unit$ #hese units are Hoined by α=β=glycosidic lin/age bet*een C 7" of the glucoseunit and C 7 + of the fructose unit$

(ii) "ses

(a) ,s a s*eetening agent for 6arious food preparations3 Hams3 syrups s*eets3 etc$

(b) 2n the manufacture of sucrose octa=acetate reKuired to denature alcohol3 to ma/e paper

transparent and to ma/e anhydrous adhesi6es$

(2) /nversion of cane$s!gar : #he hydrolysis of sucrose by boiling *ith a mineral acid or byenJyme in6ertase3 produces a miture of eKual molecules of D=glucose and D=fructose$

ory)lae6orotatismiture(#hisGructose=D

5"+54lucose=D

5"+5+Sucrose

""++"+ OHCOHCOHOHC H

+ → +

+

Sucrose solution is detrorotatory$ 2ts speci.c rotation is $%$55 o+ But on hydrolysis3 it

becomes lae6orotatory$ #he speci.c rotation of D=glucose is o%++ and of D=fructose is $>+o−

#herefore3 the net speci.c rotation of an eKuimolar miture of D=glucose and D=fructose is$

ooo

+&+

>+%+−=

−+

#hus3 in the process of hydrolysis of sucrose3 the speci.c rotation changes from o%$55+ too+&− 3 i.e., from detro it becomes lae6o and it is said that in6ersion has ta/en place$ #he

process of hydrolysis of sucrose is thus termed as iver#i" "* #%!ar and the hydrolysed

Structure ofsucrose

4lycoside lin/age

1C

(CHOH)8

1HC

1

CH+OH

H O

O

1C

(CHOH)+

1

HC1

CH+OH

"

%

5

1CH

+OH"

+

%

5

O

orO

CH+OH

OHOH

OH

4lycosidelin/age

O

"

+8

:

%

5

CH+OH5

OH

OH+

8:

%

CH+OH

"

O



Biomolecules 21

miture ha6ing eKual molar Kuantities of D=glucose and D=fructose is called ivert #%!ar. #he

enJyme that brings the in6ersion is named as iverta#e.

(3) Distinction between gl!cose and s!croseTe#t &%("#e S%(r"#e

Tith conc$ H+%O: in cold !o eect Charring occurs and turns blac/

MolischOs reagent Violet ring is formed Violet ring is formed

Tith aOH #urns yello* !o eect

Tith #ollenOs Solution 4i6es sil6er mirror !o eect

Tith GehlingOs solution 4i6es red precipitate of Cu+O !o eect

n heating *ith phenyl hydraJine 4i6es yello* precipitate of

glucosaJone

!o eect3 i$e$3 does not form

osaJone

,Kueous solution I resorcinol I

HCl (conc$)

!o eect eddish=bro*n precipitate *hich

dissol6es in ethanol$

11.3 4olysaccharide : Starch and cell!lose2.

Polysaccharides are polymers of monosaccharides$ #he most important polysaccharides are

starch and cellulose$ #hey ha6e a general formula $)( %"&5 nOHC Starch (,mylum) is most *idely

distributed in 6egetable /ingdom$ 2t is found in the lea6es3 stems3 fruits3 roots and seeds$Concentrated form of starch is present in *heat3 corn3 barley3 rice3 potatoes3 nuts3 etc$ 2t is themost important food source of carbohydrates$

(1) Starch and its derivatives : Starch is a *hite amorphous substance *ith no taste or smell$

Then heated to a temperature bet*een 3+%&+&& Co

− it changes into detrin$ ,t higher

temperature charring occurs$ Then boiled *ith dilute acid3 starch ultimately yields glucose$

4lucose5"+5

Maltose""++"+

Detrin

%"&5Starch

%"&5 ")()( OHCOHCOHCOHCnn → → →

Both n and 3"n are un/no*n3 but n is belie6ed to be greater than "n $

Then treated *ith enJyme3 diatae, it yields maltose$

Maltose""++"++%"&5 )(+ OHnCOnHOHC n → +

Starch solution gi6es a blue colour *ith a drop of iodine *hich disappears on heating to

Co'&;%− and reappears on cooling$ #he eact chemical nature of starch 6aries from source to

source$ E6en the starch obtained from same source consists of t*o fractions (i) amylose and (ii)amylopectin$

,mylose is a linear polymer *hile amylopectin is a highly branched polymer$ Both arecomposed of α=D=glucose units lin/ed by glycosidic lin/ages$ #he number of D=glucose units inamylose range from 5& 7 8&&$ 2t is soluble in hot *ater3 ,mylopectin consists of D=glucose unitsfrom 8&& 7 5&&$ 2t is insoluble in *ater$

α="3 :=4lycoside bonds

CH+OH

OOH

OH

O

O

CH+OH

OOH

OH

O

CH+OH

OOH

OH

O

epeating monomer

Structure of amylose

n

CH+OH

OOH

OH

O

O

CH+OH

OH

OH

O

nepeating monomer

α="3 :=4lycoside bonds epeating monomer

Structure of

CH+OH

OOH

OH

O

CH+OH

OOH

OH

O

O

CH+

OOH

OH

O

α="3 5=4lyoside bondsO



22 Biomolecules

;#e# Starch and its deri6ati6es are used

(i) ,s the most 6aluable constituent of food as rice3 bread3 potato and corn=Xour3 etc$

(ii) 2n the manufacture of glucose3 detrin and adhesi6es (starch paste)$

(iii) 2n paper and tetile industry$

(i6) 2n calico printing as a thic/ening agent for colours$

(6) !itro starch is used as an eplosi6e$

(6i) Starch=acetate is a transparent gelatin li/e mass and is used mainly for ma/ing s*eets$

:i#ti(ti" )etee !&%("#e #%(r"#e #tar(h

Te#t &%("#e S%(r"#e Star(hTith iodine solution !o eect !o eect Blue colour

Tith GehlingOs solution 4i6es red precipitate !o eect !o eect

Tith #ollenOs reagent 4i6es sil6er mirror !o eect !o eect

Tith phenyl hydraJine Gorms yello* osaJone !o eect !o eect

Solubility in *ater Soluble Soluble 2nsoluble

#aste S*eet S*eet !o taste

(2) Cell!lose and its !ses : 2t is found in all plants and so is the most abundant of all

carbohydrates$ 2t is the material used to form cell *alls and other structural features of the

plants$ Tood is about %& cellulose and the rest is lignin$ Cotton and paper are largely

composed of cellulose$Pure cellulose is obtained by successi6ely treating cotton3 *ool3 Xa or paper *ith dilute

al/ali3 dilute HCl or H0 $ #his treatment remo6es mineral matter3 *ater3 alcohol and ether$

Cellulose is left behind as a *hite amorphous po*der$

Cellulose is insoluble in *ater and in most of the organic sol6ents$ 2t decomposes on heating

but does not melt$ 2t dissol6es in ammonical copper hydroide solution (Sch*itJerOs reagent)$

Cellulose also dissol6es in a solution of Jinc chloride in hydrochloric acid$

Then it is treated *ith concentrated :+%OH in cold3 it slo*ly passes into solution$ #he

solution *hen diluted *ith *ater3 a starch li/e substance amyloid is precipitated and is called

par(h$et paper. Then boiled *ith dilute:+

%OH 3 it is completely hydrolysed into D=glucose$

4lucose5"+5+

Cellulose%"&5 )( OHnCOnHOHC n → +



Biomolecules 23

#he cattle3 goats and other ruminants can feed directly cellulose (grass3 stra*3 etc$) as they

ha6e digesti6e enJymes (celluloses) capable of hydrolysing cellulose into glucose$ Man and many

other mammals lac/ the necessary enJymes in their digesti6e tract and thus cannot usecellulose as food stu$

Cellulose is a straight chain polysaccharide composed of D=glucose units *hich are Hoined by

&=glycosidic lin/ages bet*een C=" of one glucose unit and C=: of the net glucose unit$ #he

number of D=glucose units in cellulose ranges from 8&& to %&&&&$

;#e# Cellulose is used

(i) ,s such in the manufacture of cloth (cotton)3 can6as and gunny bags (Hute) and paper(*ood3 bamboo3 stra*3 etc$)

(ii) 2n the form of cellulose nitrates for the manufacture of eplosi6es (gun=po*der)3medicines3 paints and lacKuers$ #he cellulose nitrates *ith camphor yield celluloid *hich is usedin the manufacture of toys3 decorati6e articles and photographic .lms$

(iii) 2n the form of cellulose acetate for the manufacture of rayon (arti.cial sil/) and plastics$

11.5 4roteins and amino acids.

Pr"tei# Proteins are a class of biologically important compounds$ #hey are crucial to6irtually all processes in li6ing systems$ Some of them are hormones *hich ser6e as chemical

messengers that coordinate certain biochemical acti6ities$ 2nsulin3 for eample3 controls the le6el of sugar in the blood stream$ Some proteins ser6e to transport the substances through the organism$aemoglobin3 for instance3 carries oygen in blood stream and deli6ers to dierent parts of the body$α =/eratin3 ser6es as a maHor constituent of hairs3 nails and s/in3 *hile collegen is the primeconstituent of tendons$ Proteins are also found in toins (poisonous materials) as *ell as inantibiotics$

A$i" a(i+# ,n amino acid is a bifunctional organic molecule that contains both acarboyl group3 7 COOH3 as *ell as an amine group3 7H+$ #hey are classi.ed as acidicbasic or neutral according to number of amine and carboyl groups in a molecule$ !eutral aminoacids contain only one amine and one carboyl group$ #hey are further classi.ed according tothe position of amine group in relation to carboyl group into α =3 β =3 γ =and δ -amino acids$ ut of

these α =amino acids are most important as they are building bloc/s of bio=proteins$2n an α =amino acid3 the amine group is located on the carbon atom adHacent to the carboyl

group (the α =carbon atom)$ #he general structure of the α =amino acids is represented as

may be al/yl3 aryl or any other group$

#he proteins dier in the nature of R=group bonded to α =carbon atom$ #he nature of R=group

determines the properties of proteins$ #here are about +& amino acids *hich ma/e up the bio=

H8C8

H+

R – – COOH

← ,mine group

α =Carbon atom

Carboyl group

7O

H

CH+OH

O

HOH

H OH

H

O

H

OH H

HO

CH+OH

OHH

O

H H H

OH H

OHH

H

O

CH+OH

O

H OHH

CH+OH

O

H

OHH

H H

O

CH+OH

H

H

O

H H

O

H OH

OH

H

OCH

+OH

H OH

H

O7H OH H

Structure of celluose



24 Biomolecules proteins$ ut of these "& amino acids (non=essential) are synthesised by our bodies and rest are

essential in the diet (essential amino acids) and supplied to our bodies by food *hich *e ta/e

because they cannot be synthesised in the body$ #he α =amino acids are classi.ed into thefollo*ing four types$

A$i" a(i+# ith " p"&ar #i+e (hai Eamples are <

Na$e Str%(t%re Three &etter

#-$)"&

Oe &etter

("+e

4lycine9ly 9

,lanine

!la !

Valine :al :

Leucine Leu L

2soleucine *L5 *

Phenyl alanine $H5 0

Proline $ro$

Amino acids with polar but neutral side chain: 56am"le are

#ame StructureThree letter

symbol

%ne letter

code

#ryptophan ;r". 3

CH+

H+

COOH

CH8CH

H+

COOH

(Essential)

(CH8)

+CH7CH

H+

COOH

(CH8)+CH7CH+CH

H+

COOH(Essential)

H+C CH

+

H+C CHCOOH

H

H+

COOHC

+H

%7CH–CH8

CH8

(Essential)H

+

COOHC

5H

%CH

+CH

(Essential)

H8

CH81C

– CH+

– COOH

H+

8

(Essential)



Biomolecules 25

Serine %er %

#hreonine ;hr ;

#yrosine ;yr <

Cysteine Cy C

Methionine Met M

,spargine !n

4lutamine 9ln =

Amino acids with acidic side chains : 56am"le are

,spartic acid !" D

4lutamic acid 9lu 5

Amino acids with basic side chains : 56am"le are

Lysine Ly >

,rginine !rg R

HO–CH+–CH

H+

COOH

CH8CHOH–CH

H+

COOH(Essential)

HO CH+7CH–COOH

H+

8

H%–CH+–CH

H+

COOH

H+

COOH

H+

O

C?CH+?CH

+YCH

H+

COOH

H+

O

C?CH+YCH

CH8?%?CH

+?CH

+?CH

H+

COOH

(Essential)

H+

COOH

HOOC?CH+?CH

H+

COOH

HOOC?CH+?CH

+CH

H+

COOH

H+!(CH

+)

:CH

(Essential)

(Essential)

H+

COOH

C?H.(CH+)

8CH

H+

H



26 Biomolecules

istidine Hi H

(Essential)

H+

COOH

C CH+ CH

CH

H

HC

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Biomolecules Part