516
CHAPTER16 Carbohydrates
lilt|
Chitin,heporin,and ocid mucopolysa'cchorides
AIM: To nomeond choroderizethe sourceof socchorides
contoining functional groups other than hydroxyl ond
corbonyl.
Saccharides may contain
fu nctional groups other ttran
carbonyl and hydrorvl.
T\tro monosaccharides that contain functional groups o_.therthari-carbonyl
and hydroryl are glucuronic acid and glucosamine. They areg€lated structurally and stereochemically to o-glucose. N-Acetylglucosamin? is also
found in many polysaccharides and is formed from glucosamine.
Glucuronic acid
Glucosamine
tH,on
J-O
t/t
\
KoH )*oH
"oH NH
I
zzc'..
o
cH3
N-Acetylglucosamine
Chitin is an example of a polysaccharide that contains N-acerylglucosamine. Chitinforms the shells of crustaceans:crabs,lobsters;.and shrimp. It
is also a major constituent of the hard skeletons of insects. Chitin is composed of repeating units of N-acetylglucosamine:
. -e
cH2oH
/
i-"vA
J\*'/
/
f---l
NH
(
NH
(
-C
trr,
,C
t"r,
Chitin
.C
l6.lO Chitin,Heparin,and AcidMucopolysaccharidesjl7
chitin is insoluble in water and is very resistant to hydrolysis of its component saccharides.
Acid mucopolysaccharides are uiscouspolysaccharidesthat containN acetylglucosamine and glucuronic acid. Hyah,tronic acid is an acid
mucopolysaccharide. It consists of repeating units of N-acetylglucosamine
linked to glucuronic acid. The bonding pattern is
o
co2H
cH2oH /'
l-o
Ho\
\rofr
Aq" ,/
/-\
l-1"
,/
o-t-1
"J\,
,/
T'
l'",,
NH
I
/c".
o
cH.
uronic acid
Hyaluronic acid is found in the connective tissue of animals, where it acts
as a glue that helps to hold cells together. Another acid mucopolysaccharide is heparin, an important natural btood anticoagulant:
Grucuronicacid
tt\
fr?*'"
surrateunitt"T1t^"\L_{o'
oso3H
Glucosamine
sulfate unit
NHSO3H
Heparin
The use of anticoagulant
drugs such as heparin may cause
abnormal bleeding in different
parts of the body. Treatment is
monitored through the use of
periodic blood clotting tests.
Using aspirin or alcoholwhen
taking anticoagulant drugs can
increase the chance of abnormal
bleeding.
Heparin is sometimes used to reduce the possibility of the formation of
blood clots in the arteries of people who are at risk of heart attack or who
have undergone heart bypass surgery.
518
CHAPTER
l6 Carbohvdrates
PRACTICE
EXERCISE
I6.I6
Howmanyfunctional groups canyou identiffin the following structure?
cH2oH
/-\
\9H
noHl /
HOI
o
I
H
CH,
,f-",t-LJ \
Kq"X 'l \:/
roH
OH
su&,1ffiRRV
Simple sugars, called monosaccharides,are polyhydroxy aldehydes (aldoses)or ketones (ketoses).
All sugarscontain at least one asyrnmetric carbon.
An important aspect of sugar chemistry is stereochemistry-relating the positions of groups of a
compound in space.There is one pair of stereoisomers for compounds containing one asymmetric
carbon. Stereoisomers have the same molecular
formula, but they are nonsuperimposable mirror
images. Stereoisomersmay be called optical isomers becausethey rotate plane-polarized light.
Straight-chainaldosesand ketosesform hemiacetal and hemiketal rings, respectively.The heterocyclic ether rings are five-membered (furanoses)and
six-membered(pyranoses).Fischerprojections represent straight-chain sugan; Haworth projections represent sugarsin ring forms. Cyclization of a straightchain sugar to a pyranose or furanose ring createsa
new asymmetric carbon in the molecule. Molecules
whose stereochemistrydiffers only at the newly created asgnmetric carbon are called anomers.
Simple sugars are often linked to other sugars
through glycosidic bonds to create disaccharides.
Polysaccharides are sugars containing many
monosaccharideunits.
Starchesare polymers of glucose from plants.
One form, which is a linear polymer, is amylose.
Another, which is a branched polymer, is amylopectin. Glycogen is the animal form of starch; it
is more highly branched than amylopectin. Cellulose is another linear polymer of glucose.Cellulose
is more resistant to hydrolysis than starch. Many
other polymers of monosaccharides are found in
nature, where they have many diverse functionsfrom forming the hard shells of crabs,like chitin, to
acting as a blood anticoagulant, like heparin.
Reducing sugars give positive results in the
form of a red precipitate with Benedict'sreagent or
a silver mirror with Tollens' reagent. Nonreducing
sugars do not. Most monosaccharides and disaccharides except sucroseare reducing sugars.Most
polysaccharidesare nonreducing sugars.
K M Yg g R € W S
Acid mucopolysaccharide
(16.10)
Aldose(16.1)
Anomer (16.4)
As1'rnmetriccarbon (16.l)
Carbohydrate(16.1)
Cellulose(16.6)
Disaccharide(16.7)
Fischerprojection (16.1)
Furanosering system
(r6.3)
Glycogen(16.6)
Glycoside(16.5)
Glycosidicbond (16.5)
Haworth projection (16.4)
Invert sugar (16.8)
Ketose(16.2)
Monosaccharide(16.2)
Nonreducingsugar (16.9)
Nonsuperimposable
mirror image (16.1)
Optical isomer (16.1)
Plane-polarized light
(16.1)
Polysaccharide(f 6.6)
Pyranosering system
(16.3)
Reducingsugar (16.9)
Simple sugar (16.2)
Starch(16.6)
Stereoisomer(16.1)
Sugar(16.1)