261
Biomolecules 5
Chapter Chapter
""
CHAPTER CONTENTS 11.1 Carbohydrates 11.2 Monosaccharides 11.3 Disaccharides 11.4 Polysaccharide (Starch and cellulose) 11.5 Proteins and amino acids 11.6 !ucleic acids
11.7 Lipids 11.8 Energy cycle or Metabolism 11.9 Digestion of food 11.10 Vitamins 11.11 ormones Assignment (Basic and Advance Advance Level) Answer Sheet of Assignment Assignment
262 6 Biomolecules
All living bodies are composed of several lifeless lifeless substances which are present in their cells in a very complex but highly organised form. These are called biomolecules. biomolecules. Some common examples are carbohydrates, proteins, enzymes, nucleic acids, lipids, amino acids, fats etc : Livi! "r!ai#$s "r!ai#$ s
Or!a#
Ti##%e#
Ce&&#
Or!ae&&e#
'i"$"&e(%&e#.
11.1 Carbohydrates. Carbohydrates. #he carbohydrates are naturally occurring organic substances$ #hey are present in both plant plants s and and anim animal als$ s$ #he #he dry dry mass mass of plan plants ts is comp compos osed ed of %& to '& '& of the the poly polyme meri ric c carbohydrate cellulose$ Carbohydrates are formed in the plants by photosynthesis from carbon dioide and *ater$ nCO+
+
Light
→ (CH +O)n nH+O
Chlorophyl l
+
nO+
,nimals do not synthesise carbohydrates carbohydrates but depends on plants for their supply$ supply$ (1) Defination Defination : -Carbohydrates are de.ned as a class of compounds that include polyhydric aldehy aldehydes des or polyhy polyhydri dric c /etones etones and large large polym polymeri eric c compou compounds nds that that can be bro/ bro/en en do*n do*n (hydrolysed) (hydrolysed) into polyhydric aldehydes or /etones$0 /etones$0 Carbohydr Carbohydrates ates contain contain > C = O an and − OH groups$ , carbonyl compound reacts *ith an alcohol to form hemiacetal$ R− C 1 H
=
O
+
,ldehyde
H 1 ′ → → − HOR R C − OH ,lcohol 1 OR′ emiacetal
2n carb carboh ohyd ydra rate tes3 s3 the the carb carbon onyl yl grou group p comb combin ine e *ith *ith an alco alcoho holic lic grou group p of the the same same molecules molecules to form form an internal internal hemiaceta hemiacetall thus the corre correct ct de.nation de.nation of carbohydr carbohydrates ates is as follo*s -, polyhydroy compound that has an aldehydic or a /etonic functional group either free or as hemiacetal or acetal$0 H
O C 1 CHOH 1 CHOH 1 CHOH 1 CHOH 1 CH+OH
4lucose (C (C5H"+O5)
H
OH
C 1 CHOH 1 CHOH 1 CHOH 1 CH 1 CH+OH ,n internal hemiacetal
O
Biomolecules 7 2n general3 carbohydrates are *hite solids3 sparingly soluble in organic sol6ents and (ecept certain polysaccharides) are soluble in *ater$ 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 8 : % 5 ;
A&+"#e
,et"#e
,ldotriose ,ldotetrose ,ldopentose ,ldoheose ,ldoheptose
9etotriose 9etotetrose 9etopentose 9etoheose 9etoheptose
(3) Classification : #he complete class.cation of carbohydrates may be depicted in short in
the follo*ing chart <
Carbohydrates
Sugars
Monosaccharides
,ldoses
!on=sugars (Polysaccharides ) eteropoly 7 saccharides
omopoly 7 saccharides
ligosaccharides
9etoses
Disaccharide s 11." #onosaccharides.
#risaccharide s
#etrasaccharid es
$$
$$
$$
#hese are the simplest one unit non=hydrolysable sugars$ #hey ha6e the general formula Cn H +nOn *here n 6aries from 8 to > carbon atoms$ ,bout +& monosaccharides occur in nature$ #he simplest are trioses (n?8) H
C8 H 5O8 @ #riose
−C =
O
1 H − C − OH @ 1 CH +OH 4lyceralde hyde
CH +OH
1 C
=
O
1 CH +OH Dihydroya cetone
#he most important naturally occurring monosaccharides are pentoses and heoses$ , common pentose is ribose and t*o common heoses are glucose and fructose$ Ecept /etotriose Adihydroyacetone3 all aldose and /etoses Amonosaccharides contain asymmetric carbon atoms and are optically acti6e$ !umber of isomers depand upon the number of asymmetric carbon atom in the molecules of monosaccharide and is deri6ed by the formula + n *here n is the number of asymmetric carbon atoms in the molecules$
8 Biomolecules N%$)er "* (ar)" at"$#
#rioses 8 #etroses : Pentoses % eoses 5
CH+OHCHOHCHO CH+OHCOCH+OH CH+OH(CHOH)+CHO CH+OHCHOHCOCH+OH CH+OH(CHOH)8CHO CH+OH(CHOH)+COCH+OH CH+OH(CHOH):CHO CH+OH(CHOH)8COCH+OH
N". "* a#-$$etri( (ar)" at"$# "
+ 7 : + ' : "5 '
7 + " 8 + : 8
C&a##
"&e(%&ar *"r$%&a
,ldotrioses ,ldotetroses ,ldopentoses ,ldoheoses
C8H5O8 C:H'O: C%H"&O% C5H"+O5
Str%(t%ra& *"r$%&a A&+"#e# CH+OHCHOHCHO CH+OH(CHOH)+CHO CH+OH(CHOH)8CHO CH+OH(CHOH):CHO
C8H5O8 C:H'O: C%H"&O% C5H"+O5
,et"#e# CH+OHCO.CH+OH CH+OH.CO.CHOH.CH +OH CH+OH$CO$(CHOH)+CH+OH CH+OH.CO(CHOH)8CH+OH
9etotrioses 9etotetroses 9etopentoses 9etoheoses
N". "* i#"$er#
E/a$p&e#
4lyceraldehyde Erythrose3 #hreose ,rabinose3 ibose3 Fylose3 Lyose 4lucose3 4alactose3 Mannose3 ,llose3 #alose3 4ulose3 2dose3 etc$ Dihydroyacetone Erythrulose ibulose3 Fylulose Gructose3 Sorbose3 #angatose3 Psicose
(1) D and L$designation : By ("veti" a molecule is assigned D=con.guration if the 7 OH
group attached to the carbon adHacent to the 7CH+OH group (last chiral carbon) is on the right hand side irrespecti6e of the position of other groups$ 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 CHO.CHOHCH OH isomers (+)" ? + +
CHO 1 H – C – OH 1 CH+OH
CHO 1 OH – C – H 1 CH+OH
D=4lyceraldehyde
L=4lyceraldehyde
(ii) Aldotetrose CHO.CHOH.CHOH.CH+OH CHO 1 H – C – OH 1 H – C – OH 1 CH+OH D=Erythrose
CHO 1 HO – C – H 1 H – C – OH 1 CH+OH D=#hreose
isomers (+)+?:
L-Erythrose
So it has four isomers3 i.e., D3 L=Erythrose and D, L=#hreose$
L- #hreose
Biomolecules 9 (iii) Aldopentose : CHO.CHOH.CHOH.CHOH.CH +OH3 isomers (+) 8 ? ' D=Erythrose CHO 1 H – C – OH 1 H – C – OH 1 H – C – OH 1 CH+OH
D=#hreose
CHO 1 OH – C – H 1 H – C – OH 1 H – C – OH 1 CH+OH
D=ibose
D=,rabinose
CHO 1 H – C – OH 1 HO – C – H 1 H – C – OH 1 CH+OH
CHO 1 HO – C – H 1 HO – C – H 1 H – C – OH 1 CH+OH
D=Fylose
D=Lyose
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 D=ibose
D=Fylose
D=,rabinose
D=Lyose
CHO CHO CHO CHO CHO CHO CHO CHO 1 1 1 1 1 1 1 1 H – C – OH HO – C – H H – C – OH HO – C – H H – C – OH HO – C – H H – C – OH HO – C – H 1 1 1 1 1 1 1 1 H – C – OH H – C – OH HO – C – H HO – C – H H – C – OH H – C – OH HO – C – H HO – C – H 1 1 1 1 1 1 1 1 HO – C – H HO – C – H HO – C – H HO – C –H H – C – OH H – C – OH H – C – OH H – C – OH 1 1 1 1 1 1 1 1 H – C – OH H – C – OH H – C – OH H – C – OH H – C – OH H – C – OH H – C – OH H – C – OH 1 1 1 1 1 1 1 1 CH OH CH OH CH OH CH OH CH+OH CH+OH CH+OH CH+OH + + + + D=,llose
D=,ltrose
D=4lucose
D=Mannose
D=4ulose
D=2dose
D=4lactose
D=#alose
(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$-!+a&i and #a&i(i. (i) Preparation (a) Laboratory method H+
C"+H ++O""+ H +O → C5 H"+O5 + C5 H"+O5 Canesugar (Sucrose)
4lucose
Gructose
!ote <
HCl (dil$) 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$ +
H (C5 H"&O% )n + nH+O → nC5 H"+O5 Starch
4lucose
, 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 reduced pressure$ 4lucose is obtained in crystalline form$ (ii) Physical properties 2t is a colourless crystalline solid3 melts at ":5o C $ 2t is readily soluble in *ater$ Grom aKueous solution3 it separates as a crystalline monohydrate (C 5 H "+O5 $H +O) *hich melts at '5o C $ 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 naturally occuring 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 7 OH 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 CHO
CHO
1
1 #nCl+
(CHOH): + %CH 8COCl →(CHOOCCH 8): + %HCl ,cetylchloride
1
1
CH +OH
CH +OOCCH 8
4lucose
4lucosepenta =acetate
#his sho*s that a molecule of glucose contains % 7 OH groups$ • eaction *ith $Cl% CHO
CHO
1 1 → (CHCl ): + %$OCl 8 (CHOH ): + %$Cl % 1 CH +OH 4lucose
+
%HCl
1 CH +Cl
Penta=chlorogluc ose (4lucosepenta =chloride)
• eaction *ith metallic hydroides < C5 H""O% L OH + H O L Ca L OH → C5 H""O% L O L Ca L OH + H +O 4lucose
Calciumhydroide
Calciumglucosate
!ote <
4lucose beha6es as a *ea/ acid$ 2nstead of Ca(OH )+ *e can ta/e other metallic hydroide li/e &a(OH)+3 %r (OH )+3Cu(OH )+ etc to form glucosate *hich is soluble in *ater$ HCl → C5 H ""O%OCH 8 + H +O • Gormation of glycosides < C5 H""O% L OH + H OCH8 N= and=Methylglucoside
H
OCH8
C 1 (CHOH)8 1 CH 1 CH+OH α=Methyl glucoside
CH'O
O
H C 1 (CHOH)8 1 CH 1 CH+OH
O
β=Methyl glucoside
#his reaction sho*s the presence of ring structure in glucose$
Biomolecules 11 (b) Reaction of carbonyl grou" (!ldehydic grou") )a− Hg → CH +OH(CHOH ): CH +OH • eduction < CH +OH(CHOH): CHO+ +H H O
4lucose
Sorbitol
+
n prolonged heating *ith concentrated H* and red phosphorus at ""&o C 3 glucose forms a miture of +=iodoheane and n=heane$ • idation eaction *ith Gehling solution < CH +OH(CHOH ): CHO+ +CuO → CH +OH(CHOH ): COOH + Cu+O $ 4lucose
4luconicacid
eaction
(red ppt$)
*ith
#ollenOs
→ CH + OH(CHOH ): COOH CH +OH(CHOH ): CHO + !g+O
eaction eaction
+!g
+
reagent
<
$
(Mirror) Qor blac/ppt$
&r + R H +O *ith Bromine *ater < CH +OH(CHOH): CHO+ QO → CH +OH(CHOH): COOH $
4lucose
4luconicacid
H)O8
*ith !itric acid < CH +OH(CHOH): CHO+ 8QO → COOH(CHOH ): COOH+ H +O $ 4lucose(C5)
Saccharic acid(C5 )
C)
• eaction *ith HC < CH +OH(CHOH ): CHO + HC) → CH +OH(CHOH ): CH 4lucosecyanohydri n
$ OH
• eaction *ith hydroyl amine
CH +OH(CHOH ): CHO + )H +OH
→
CH +OH(CHOH ): CH 4lucoseoime
=
)OH + H +O $
• eaction *ith Phenyl hydraJine (Gischers mechanism) < Then *armed *ith ecess of phenyl hydraJine3 glucose .rst forms phenylhydraJone by condensation *ith 7 CHO group$ CHO + H+HC5H% Phenyl hydraJine 1 CHOH 1 Tarm (CHOH)' 1 CH+OH
CH HC5H% 1 CHOH 1 (CHOH)' 1 CH+OH
4lucose
#he adHacent 7 CHOH group is then CH HC5H% 1 CHOH + H+HC5H% 1 (CHOH)' 1 CH+OH
#he resulting carbonyl glucosaJone$
4lucose phenyl hydraJoneby oidised
CH HC5H% 1 C O + C5H%H+ I H8 1 (CHOH)' 1 CH+OH
9eto compound of 4lucose phenyl hydraJone compounds reacts *ith
CH HC5H% 1 C O + H+HC5H% 1 (CHOH)' 1 CH+OH
a second molecule of phenyl hydraJine$
a third molecule of phenyl hydraJine to yield
CH HC5H% 1 C HC5H% I H+O 1 (CHOH)' 1 CH+OH 4lucosaJone
12 Biomolecules
(c) Micellaneou reaction #yma(e → +C+H %OH + +CO+ • Germentation < C5H"+O5 4lucose
Ethanol
• 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# $ CH OH 11 C OH
CH O 1 H C OH
… Enol
… 4lucose
O
O
H
CH+OH 1 CO
HO CH 11 HO C
… Gructose
Enol
CH O 1 HO C H
…
H
C 1 HO – C – H 1 HO – C – H 1 H – C – OH 1 H – C – OH 1 CH+OH
C 1 H – C – OH 1 HO – C – H 1 H – C – OH 1 H – C – OH 1 CH+OH
D(+) Mannose
D(+) 4lucose
Epimers
• ,ction of concentrated hydrochloric acid Conc$ HCl → CH 8COCH +CH +COOH + HCOOH C5 H "+O5
+
H +O
Lae6ulicacid
n treatment *ith conc$ C5H"+O5
HCl3 glucose
can also form hydroymethyl furfural$
CH CH + 8H O + 11 11 HOCH+ C C CHO O ydroymethyl 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$
… Mannose
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$ H +%O: 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 H +%O: 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$pt$ +&%o C $ (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 C 5 H "+O5 $ • 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 group3 > C = O 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$ OH OH OH OH OH H 1 1 1 1 1 1 U U U U HCCCCCCO 1 1 1 1 1 H H H H H
#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
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 H
O
C" 1+ H – C – OH 18 HO – C – H 1: H – C – OH 1% H – C – OH 15 CH+OH D-4lucose
Evi+e(e a!ai#t "pe (hai #tr%(t%re #he open chain formula of glucose accounts for 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 )aH%O8 and )H 8 $ 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 rotation o + ""& 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= β=D=glucose$ glucose and 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 $ #he eKuilibrium 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 in H 2n O pyranose structure$ this process .rstHcarbon gi6ing t*o isomers (2) HOasymmetric H OH atom becomes " and (22) *hich dier only in the con.guration of the .rst asymmetric carbon$ " C" 1+ CHOH 18 CHOH 1: CHOH 1% CHOH 15 CH+OH
C 1+ CHOH 18 CHOH 1: CHOH 1% CH 15 CH+OH
D-4lucose
QαD ? I %+$% α=4lucose 85
o
O
C 1+ CHOH 18 CHOH 1: CHOH 1% CH 15 CH+OH
O
α -D-4lucose (2)
β -D-4lucose (22)
QαD ? I ""& o
QαD ? I ">$;o
pen chain form &$&+
β=4lucose 5:
Biomolecules 15
Carbon=" in both con.guration (2) and (22) is called an anomeric carbon atom$ 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$3 • α= and β=glucose on treatment *ith methyl glucosides respecti6ely$ H – C – OH 1 H – C – OH 1 HO – C – H 1 H – C – OH 1 H–C 1 CH+OH
O
CH 8OH
in presence of dry
+ CH8OH
(Dry HCl gas)
α -D=4lucose (2)
HCl
gas forms α= and β=
H – C – OCH 8 1 H – C – OH 1 HO – C – H 1 H – C – OH 1 H–C 1 CH+OH
O
α -D=Methyl glucoside
HO – C – H 1 H – C – OH 1 HO – C – H 1 H – C – OH 1 H–C 1 CH+OH
O
+ CH8OH
(Dry HCl gas)
β -D=4lucose (22)
CH'O – C – H 1 H – C – OH 1 HO – C – H 1 H – C – OH 1 H–C 1 CH+OH
O
β -D=Methyl glucoside
• N" rea(ti" ith #$3 a+ #a$S%3 #he glucose ring is not 6ery stable$ 2t is easily bro/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 Qα D
o
+ ""& $
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 rotation3 Qα D + ">$;o 3 on /eeping (standing) gradually changes into the same eKuilibrium miutre (ha6ing3 speci.c rotation
16 Biomolecules +
%+$;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 :
8
|| %
|| +
CH CH CH
CH
"
O
Guran
o*e6er according to a*orth and irst the ring is formed bet*een C " and the ring is P-ra t-pe or 5=membered ring3 this is called P-ra"#e #tr%(t%re.
C
%
$ 2t means
CH+
: 8
%
HC
CH
||+
|| 5
HC
CH
"
O
Pyran
#he t*o forms of D=glucose are also sho*n by Ha"rth proHection formula *hich are gi6en belo*@ 5CH+OH %
H :
H OH
5CH+OH
O H
OH
H "
:
OH 8
+
OH H α -D glucose
%
H H OH
O H
OH "
OH
H 8
+
OH H β -D glucose
#he abo6e proHection formulae sho* that the si membered ring is planar but actually the ring 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 CH +OH 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 combined form$ #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 H +%O: (dil$) H ++O""+ H +O → C5 H "+O5 + C5 H "+O5 (a) Hydrolyi of cane ugar C"+ Tarm Canesugar D=4lucose D=Gructose
#he solution ha6ing eKual molecules of D=glucose and D=fructose is termed ivert #%!ar and the process is /no*n a# iver#i"$
!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$
Biomolecules 17 C 5 H ""O% − O − CaOH+ CO + → C 5 H "+O5 + CaCO8 Calciumfructose
Gructose
H +%O: (dil$) → nC5 H "+O5 (b) Hydrolyi of *nulin 2ith dilute ul"huric acid (C 5 H "&O% )n + nH +O 2nulin
Gructose
(ii) Properties #he anhydrous fructose is a colourless crystalline compounds$ 2t melts at "&+ C$ 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 $%tar"tati". Gructose is a pentahydroy /etone and its open=chain and closed=chain structures can be represented as < o
CH+OH 1 C O 1 HO – C – H 1 H – C – OH 1 H – C – OH 1 CH+OH
HOH+C
or
OH
C 1 HO – C – H 1 H – C – OH 1 H – C – OH 1 CH+
CH+OH 1 C O 1 (CHOH)8 1 CH+OH
D-0ructoe Qα D ? 7 >+o
(5) Comarison between gl!cose and fr!ctose
α - D- Gructose QαD ? 7 +"o
&%("#e
OH
O
CH+OH
C 1 HO – C – H 1 H – C – OH 1 H – C – OH 1 CH+
O
β - D- Gructose QαD ? 7 "88 o
Pr"pertMolecular formula !ature Melting point ptical acti6ity of natural form Tith ethyl alcohol idation
C5H"+O5 Polyhydroy aldehyde$ ":5oC Detrorotatory ,lmost insoluble
C5H"+O5 Polyhydroy /etone "&+oC Lae6orotatory More soluble
(a) Tith bromine *ater (b) Tith nitric acid
4luconic acid Saccharic acid (4lucaric acid)
eduction Calcium hydroide
Sorbitol Gorms calcium glucosate3 soluble in *ater Gorms a 6iolet ring 4i6es red precipitate Gorms sil6er mirror Gorms osaJone !o colouration
!o reaction Miture of glycollic acid3 tartaric acid and trihydroy glutaric acid Miture of sorbitol and mannitol Gorms calcium fructosate3 insoluble in *ater Gorms a 6iolet ring 4i6es red precipitate Gorms sil6er mirror Gorms osaJone 4i6es red or bro*n colour or precipitate Bluish green colour on heating
MolischOs reagent GehlingOs solution #ollenOs reagent Phenyl hydraJine esorcinol I HCl (dil$) (Seli6anoOs test) Greshly prepared ammonium Light blue colour molybdate sol$ I fe* drops of acetic acid (Pi"# te#t)$ ,lcoholic I HCl !o colouration α=naphthol (conc$) (%r*%ra& te#t)
r%(t"#e
, purple colour (6iolet) on boiling
18 Biomolecules
!ote <
Gructose gi6es reactions similar to glucose$ #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$ CHO 1 (CHOH)8 1 CH+OH
HC
,rabinose (,ldopentose)
COOH C 1 1 CHOH CHOH H+O4H+ 1 1 &a(OH)+ (CHOH) (CHOH)8 8 1 1 CH+OH CH+OH 4luconic acid
OC– 1 CHOH heat 1 –H+O CHOH 1 CH 1 CHOH 1 CH+OH
OC–H 1 CHOH a – Hg 1 in acid (CHOH)8 1 solution CH+OH
O
4lucose (,ldoheose)
γ =Lactone
(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 in6ol6es t*o steps< • idation of the aldose to aldonic acid by using bromine *ater$ • #he aldonic acid is treated *ith CaCO8 to gi6e the calcium salt *hich is then oidised by
GentonOs reagent ( H +O+ + ferric sulphate) to form the net lo*er aldose$ CHO 1 CHOH 1 (CHOH)8 1 CH+OH
&r + H+O
,ldoheose (D=4lucose)
COOH 1 CHOH 1 (CHOH)8 1 CH+OH
Ca- alt H+O+I0e8I
,ldonic acid
(b) &y 3ohl method < 2t in6ol6es the follo*ing steps
CHO 1 (CHOH)8 1 CH+OH ,ldopentose (D=,rabinose)
• 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$ CH O 1 CHOH 1 (CHOH)8 1 CH+OH
4lucose (,ldoheose)
H+OH
CH OH C 1 1 CHOH CHO.COCH ' !gOH (CH8CO)+O 1 1 *arm (CHOH)8 (CHO.COCH 8)8 1 1 CH+OH CH+O.COCH' ime
C 1 CHO CHO H 1 – HC 1 (CHOH)8 (CHOH)8 1 1 CH+OH CH+OH ,ldopentose
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$ CHO 1 CHOH 1 (CHOH)8 1 CH+OH
HCHC5H% 1 CHC5H% 1 7H+O4H+ (CHOH)8 (–7C5H%HH+) 1 CH+OH
C5H%HH+ (56ce)
4lucose
saJone
HCO 1 CO 1 (CHOH)8 1 CH+OH
7H #nRCH8COOH
sone
CH+OH 1 CO 1 (CHOH)8 1 CH+OH Gructose
(i6) onversion of a (etose to the isomeric Aldose #*o steps are in6ol6ed3 (a) eduction of a /etose *ith H + R )i to form polyhydric alcohol$ (b) idation *ith GentonOs reagent to form aldose$ CH+OH 1 CO 1 (CHOH)8 1 CH+OH
H+ 4i
CH+OH 1 CHOH 1 (CHOH)8 1 CH+OH
Gructose
QO H+O+ + 0e8I
CHO 1 CHOH 1 (CHOH)8 1 CH+OH 4lucose
11.0 Disaccharides. #he disaccharides yield on hydrolysis t*o monosaccharides$ #hose disaccharides *hich yield t*o heoses on hydrolysis ha6e a general formula C"+H ++O""$ #he heoses obtained on hydrolysis may be same or dierent$ H +O C"+H ++O"" → C5 H"+O5 + C5 H"+O5 H+
Sucrose
4lucose
Gructose
H+O
Lactose → 4lucose I 4alactose H
+
H+O
Maltose → 4lucose I 4lucose H
+
#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$
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 "'5 oC$ 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 glucose unit and C 7 + of the fructose unit$ 4lycoside lin/age
5CH+OH %
O
4lycoside lin/age :
H
"CH
OH + 1 + C C 1 1 (CHOH) (CHOH)8 + %1 %1 O O HC HC 1 1 5 5 CH+OH CH+OH O
"
OH
OH
"
+ 8
OH
or
O 5
CH+OH
%
O
: 8 Structure of
+
OH
CH+OH
"
OH
sucrose (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$s!gar : #he hydrolysis of sucrose by boiling *ith a mineral acid or by enJyme in6ertase3 produces a miture of eKual molecules of D=glucose and D=fructose$ +
H → C 5 H "+O5 + C 5 H "+O5 C"+H ++O""+ H +O Sucrose
D=4lucose
D=Gructose
(#hismitureis lae6orotat ory)
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$ o
o
+ %+ − >+
+
o
= −+&
55$%o to o − +& 3 i.e., from detro it becomes lae6o and it is said that in6ersion has ta/en place$ #he process of hydrolysis of sucrose is thus termed as iver#i" "* #%!ar and the hydrolysed #hus3 in the process of hydrolysis of sucrose3 the speci.c rotation changes from
+
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!crose Te#t Tith conc$ H+%O: in cold MolischOs reagent Tith aOH Tith #ollenOs Solution Tith GehlingOs solution n heating *ith phenyl hydraJine
&%("#e
S%(r"#e Charring occurs and turns blac/ Violet ring is formed !o eect !o eect !o eect of !o eect3 i$e$3 does not form osaJone eddish=bro*n precipitate *hich dissol6es in ethanol$
!o eect Violet ring is formed #urns yello* 4i6es sil6er mirror 4i6es red precipitate of Cu+O 4i6es yello* precipitate glucosaJone ,Kueous solution I resorcinol I !o eect HCl (conc$)
11.3 4olysaccharide : Starch and cell!lose2. Polysaccharides are polymers of monosaccharides$ #he most important polysaccharides are starch and cellulose$ #hey ha6e a general formula (C5 H"&O% )n$ 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 the most 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 +&&− +%&o C3 it changes into detrin$ ,t higher temperature charring occurs$ Then boiled *ith dilute acid3 starch ultimately yields glucose$ (C5H"&O%)n → (C5 H"&O% )n → C"+H ++O"" → C5 H"+O5 " Starch
Maltose
Detrin
4lucose
Both n and n"3 are un/no*n3 but n is belie6ed to be greater than Then treated *ith enJyme3 diatae, it yields maltose$ +(C5H"&O% )n + nH+O → nC"+H ++O""
n" $
Maltose
Starch solution gi6es a blue colour *ith a drop of iodine *hich disappears on heating to ;% − '&o C 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 are composed of α=D=glucose units lin/ed by glycosidic lin/ages$ #he number of D=glucose units in amylose range from 5& 7 8&&$ 2t is soluble in hot *ater3 ,mylopectin consists of D=glucose units from 8&& 7 5&&$ 2t is insoluble in *ater$ CH+OH
CH+OH
CH+OH O O
OH
O O
CH+OH O
OH
epeating monomer
OH
O n
OH
O
OH
O
OH
CH+OH O OH
O
OH
α="3 5=4lyoside bondsO
OH
OH epeating monomer
α="3 :=4lycoside bonds
CH+OH
CH+ Structure of amylose O
O
OH
n
CH+OH O
O OH
O
OH
O O
OH α="3 :=4lycoside bonds
Structure of
OH
O OH
epeating monomer
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(h
Tith 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
S*eet
S*eet
!o taste
#aste
(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 H +%O: 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$et paper. Then boiled *ith dilute H +%O: 3 it is completely hydrolysed into D=glucose$ (C5 H "&O% )n + nH+O → nC5 H "+O5 Cellulose
4lucose
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 use cellulose 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 %&&&&$ H H 7O OH H
H
OH
CH+OH O O OH H H H H O O O H H H H H H H OH O CH+OH H OH OH
CH+OH
H
OH
CH+OH O OH H H H H O O H OH H H H O CH+OH H OH
H OH
OH H H
H
O7
O CH+OH
Structure of celluose ;#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$) (ii) 2n the form of cellulose nitrates for the manufacture of eplosi6es (gun=po*der)3 medicines3 paints and lacKuers$ #he cellulose nitrates *ith camphor yield celluloid *hich is used in 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 to 6irtually 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 prime constituent of tendons$ Proteins are also found in toins (poisonous materials) as *ell as in antibiotics$ A$i" a(i+# ,n amino acid is a bifunctional organic molecule that contains both a carboyl group3 7 COOH3 as *ell as an amine group3 7H+$ #hey are classi.ed as acidic basic or neutral according to number of amine and carboyl groups in a molecule$ !eutral amino acids contain only one amine and one carboyl group$ #hey are further classi.ed according to the 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 Carboyl group H 8 R – C – COOH 8 H+← ,mine group α =Carbon atom 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=
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 the follo*ing four types$ A$i" a(i+# ith " p"&ar #i+e (hai Eamples are < Na$e
Str%(t%re
4lycine
9ly
9
!la
!
:al
:
Leu
L
*L5
*
$H5
0
COOH
,lanine
H+ CH8CH
COOH
Valine
H+ (CH8)+CH7CH
COOH
(Essential) Leucine
H+ (CH8)+CH7CH+CH (Essential)
2soleucine
Proline
Oe &etter ("+e
H+ CH+
Phenyl alanine
Three &etter #-$)"&
COOH H+
C+H%7CH–CH 8 COOH CH8 (Essential) H+ C5H%CH+CH COOH (Essential) H+C
CH+
H+C
CHCOOH
$ro
$
Amino acids with polar but neutral side chain: 56am"le are #ame
#ryptophan
Structure
H
H 8
H+ CH 8 81 – CH – COOH + C (Essential)
Three letter symbol ;r".
%ne letter code 3
Biomolecules 25
Serine
H+
%er
%
;hr
;
;yr
<
Cy
C
Met
M
!n
9ln
=
!"
D
9lu
5
Ly
>
!rg
R
HO–CH+–CH COOH #hreonine
H+ CH8CHOH–CH COOH (Essential)
#yrosine
H+ 8 CH+7CH–COOH
HO Cysteine
H+ H%–CH+–CH COOH
Methionine
H+ CH8?%?CH+?CH+?CH COOH
(Essential) ,spargine
H+
H+ C?CH+YCH COOH
O 4lutamine
H+
H+ C?CH ?CH YCH
+ Amino acids with acidic side chains :+ 56am"le are
COOH
O
,spartic acid
H+ HOOC?CH +?CH COOH
4lutamic acid
H+ HOOC?CH +?CH+CH
Amino acids with basic side chains : 56am"le are
COOH
Lysine
H+ H+!(CH+):CH
,rginine
H H+
COOH H+ (Essential) C?H.(CH +)8CH COOH (Essential)
26 Biomolecules
istidine
H+ HC
C CH+ CH COOH H
CH
(Essential)
Hi
H
