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