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20 Chapter 20, actually (CHPT 19)
Carbohydrates
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20-1
20 Carbohydrates
•Carbohydrate: a polyhydroxyaldehyde or polyhydroxyketone,
•or a substance that gives these compounds on hydrolysis.
Most simple carbos = Saccharides
e.g. monosaccharides,, oligosaccharides, polysachrides,
dep. On # of simple sugars attached
•Monosaccharide: a carbohydrate that cannot be
•hydrolyzed to a simpler carbohydrate.
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20-2
20 Monosaccharides
• general formula CnH2nOn, where n varies from 3 to 8.
C6H12O6
Two Types:
Aldose: a monosaccharide containing an
aldehyde group.
Ketose: a monosaccharide containing a
ketone group.
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20-3
20 Monosaccharides
• classified by their number of carbon atoms.
Name
Formula
Triose
Tetrose
Pentose
C3 H6 O3
C4 H8 O4
Hexose
Heptose
Octose
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C5 H1 0 O 5
C6 H1 2 O 6
C7 H1 4 O 7
C8 H1 6 O 8
20-4
20 Monosaccharides
• There are only two trioses:
CHO
CH2 OH
CHOH
C= O
CH2 OH
CH2 OH
Glyceraldehyde
(an aldotriose)
D ihydroxyacetone
(a ketotriose)
•Often aldo- and keto- are omitted
•compounds are referred to simply as trioses.
•Although “triose” does not tell the nature of the carbonyl group,
•it at least tells the number of carbons.
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20-5
20 Monosaccharides
• Glyceraldehyde, the simplest aldose, contains a
stereocenter and exists as a pair of enantiomers.
Fig 19.1
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20-6
20 Monosaccharides
•Fischer projection: a two dimensional representation
showing the configuration of stereocenters.
•Horizontal lines represent bonds projecting forward from the stereocenter.
•Vertical lines represent bonds projecting to the rear.
•Only the stereocenter is in the plane.
2,3 hydroxy propanal
CHO
H
C
R
OH
CH2 OH
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con vert to
a Fischer
projection
CHO
H R OH
CH2 OH
20-7
20 D,L Monosaccharides
• 1891, E. Fischer  arbitrary assignments D/L to
the enantiomers of glyceraldehyde.
NOTE:
R=D
L=S
CHO
H
OH
CHO
HO
H
CH2 OH
(R) D-Glyceraldehyde
[]25 = +13.5°
D
Dextrorotatory
CH2 OH
(S) L-Glyceraldehyde
[]25 = -13.5°
D
levatory
•D-monosaccharide: the -OH on penultimate carbon on right
•L-monosaccharide: the -OH on penultimate carbon on left
in a Fischer projection.
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20-8
20 D,L Monosaccharides
• Suffix “ose” indicates compound = carbo
Nature predominately makes the D form
as well “D amino acids” discussed later…
•The most common D-tetroses and D-pentoses are:
CHO
CHO
H CHOOH
HOCHO
H
HH
OH
HOH H
OH
OH
H
OH
H
OH
CH2 OH
CH2 OH
CH2 OH
CH2 OH
D-Erythrose
D-Threose
D-Erythrose D-Threose
CHO
CHO
H CHO
OH
H CHOH
HH OH
HH
H
OH
OH
H
HH OH
H OH
OH
OH
H
OH
H
OH
CH2 OH
CH2 OH
CH2 OH 2-Deoxy-D-ribose
CH2 OH
D-Ribose
D-Ribose
2-Deoxy-D-ribose
Note: “D,L” specifies configuration @ stereocenter
farthest from Carbonyl
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20-9
20 D,L Monosaccharides
The three most common D-hexoses are:
H
HO
H
H
CHO
OH
H
OH
OH
CH2 OH
D-Glucose
CHO
CHO CH2 OH CHO
H
OHH
OH C= O H
OH
HO
HHO
HO
H HO
H
H
HO H H
OHH OHHO H
H OH H
OHH OH H OH
CH2 OH CH OHCH2 OH CH OH
2
2
D-Galactose D-GlucoseD-Fructose D-Galactose
CH2 OH
C= O
HO
H
H OH
H OH
CH2 OH
D-Fructose
aka blood sugar
Human blood~65-110 mg glucose/100ml blood
I.V. bags contain 5% glucose solut.
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20-10
20 Amino Sugars
• Amino sugars: Have -NH2 group in place of an -OH group.
Only three amino sugars are common in nature:
D-glucosamine, D-mannosamine, and D-galactosamine
H
HO
H
H
CHO
OH
H
OH
OH
CH2 OH
D-Glucose
CHO
CHO
CH
OH
O O
CHO
CHO
CHO
2 CHO
2 N 2 H
N HCCH
O
H 2 NHC=
2 H
H HN H2N H2 H HN HCCH
3
3
HO
HO HOH
H H
HO HOH H
HO HOH H
4
HH H
OH
OH OH
HO 4HOH H
H HOH OH
HH H
OH
OH OH
H HOH OH
H HOH OH
CH
OH
CH22CH
OH2 OH
CH2CH
OH2 OH
CH2CH
OH2 OH
D-Galactose
D-Fructose
D-Glucosamine
D-Mannosamine D-Galactosamine
D-Galactosamine N-Acetyl-DN-Acetyl-DD-Glucosamine
D-Mannosamine
stereois
stereois
glucos
amine
(C-2(C-2
stereois
omeromer(C-4(C-4
stereois
omeromerglucos
amine
of D-glucosamineof D-glucosamine)
of D-glucosamine)
of D-glucosamine
CHO
CHO
CHO
NH
H HHN HOH
2 2
HOH HH
HOHO
HHOHOHHOH
OH
H HHOHOH
CH2 2OH
OH
CHCH
2 OH
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20-11
20 Amino Sugars
HO
N H2
H
H
OH
H2 OH
samine
is omer
amine)
H
HO
H
H
CHO O
N HCCH 3
H
OH
OH
CH2 OH
N-Acetyl-Dglucos amine
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20-12
20 Cyclic Structure of monosaccharides
•
RECALL: 17.7
•
Aldehydes and ketones react with alcohols to form hemiacetals.
•From one stereocenter (aldehyde/alcohol)  to two (hemiacetal)
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20-13
20 Haworth Projections
• D-Glucose forms these cyclic hemiacetals.
1
1 1CHO
red raw to sh ow th e -OH
CH2 OH
CHO
redraw
rawtotoshshow
owththeto
e-OH
-OH
CHO
red
on
carbon-5
close
the
OH
CH
H
OH
2OH
2 OH
5 CH
carbon-5
close
the
carbon-5
close
totothe
H5 5
OH onon
HH OH
aldeh
yd
e
on
carbon-1
OH O
HH OH
H
HO
H
aldeh
yd
e
on
carbon-1
aldeh
yd
e
on
carbon-1
HO HH
HO
H HCCCOO
H
OH
H
OH
OHHH111 H
OH
HO
OH
HH 5 OH
HO
HO
HH
H 5 5 OH
New stereogenic center
H OH
OH
HH OH
HH OH
= anomeric carbon
OH
CH2 OH
CH
CH
2 OH
2 OH
anomeric
CH2 OH anomeric
CH2 OH
D -Glucose
CH
OH anomeric
CH
CH
OH
CH
carb on
-Glucose
DD-Glucose
2O
2 OH
2O
2 OH
H
carbonon
H
H carb
OH (  )
O
O
H
H
HHH OOOH
H
HH
OH( ( ) )
+
H
H
OH
H H
H
OH
++
H
OH
OH
OH
OH
HO
HO
HHOH(  )
HHH
HO
HO
HO
HO
( ( 
))
OH
OH
HH
H OH
H OH
HH OH
HH OH
OH
OH
-D -Glucopyranose
-D -Glucopyranose
-D
-Glucopyranose
-D
-Glucopyranose
-D
-Glucopyranose
-D
-Glucopyranose
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(-D
-Glucose)
( -D -Glucos e )
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(-D
(-D-Glucose)
-Glucose)
( -D
-Glucos
( -D
-Glucose )e )
20-14
20 Haworth Projections
1
•
CHO
H
OH
HO
H
red raw to sh ow th e -OH
on carbon-5 close to the
aldeh yd e on carbon-1
In the terminology of carbohydrate chemistry,
H
OH
5
H are
OH called anomers
Stereoisomers that differ in configuration only at anomeric carbon
CH2 OH
CHO
red raw to sh ow th e -OH
D -Glucose
CH2 OH
on carbon-5 close to the
H
OH
OH
H5
aldeh
yd
e
on
carbon-1
O -CH2OH.
HOcarbon
H
anomeric
same side of ring as theH terminal
OH H C1
H
OH
HO
H
1
• β means -OH on
H
•α
5
OH
CH2 OH
H
OH
CH2 OH anomeric
CH2 OH
carb on
OH
means -OH on anomeric carbon is on side
of
the
ring H
O OH
H
( )
H
H
+
opposite from the terminal -CH2OH.
OH H
OH H
HO
HO
OH(  )
H
H OH
H OH
-D -Glucopyranose
-D -Glucopyranose
(-D -Glucose)
( -D -Glucos e )
D -Glucose
CH2 OH
O OH (  )
H
H
OH H
HO
H
H OH
-D -Glucopyranose
(-D -Glucose)
six-membered hemiacetal ring :pyranose,
five-membered hemiacetal ring: furanose.
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O
O
Furan
Pyran
20-15
20 Haworth Projections
• Aldopentoses also form cyclic hemiacetals.
The most prevalent forms of D-ribose/ other
pentoses are furanoses.
HOCH
HOCH22 OO
HOCH
HOCH22 OO
HH
OH
OH ()
()
HOCH2
HOCH2
H
OH ()
HH O
HH
HH O
HH
H
H
H
H
HH
OH
OH()
()
HH
HH
H OH
OH ()
H OH
OH
OH
OH
OH
HHH
OH
OH
H
-2-D
-2-DOH
eoxy-D
eoxy-D-ribofuranose
-ribofuranose
-D
-D-Ribofuranose
-Ribofuranose
-2-D
eoxy-D
-ribofuranose
-D -Ribofuranose
(-2-D
(-2-D
eoxy-D
eoxy-D
-rib
-ribos
ose)
e)
(-D
(-D-Rib
-Ribos
ose)
e)
(-2-D eoxy-D -rib os e)
(-D -Rib os e)
•The prefix “deoxy” means “without oxygen.”
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20-16
20 Haworth Projections
• D-Fructose (a 2-ketohexose) also forms a fivemembered cyclic hemiacetal.
HOCH2
5
1
O
H HO
CH2 OH
2
OH( )
H
HO
H
 -D -Fructofuranose
( - D -Fructos e)
1
CH2 OH
2
C=O
HO
H
H
OH
H 5 OH
CH2 OH
D -Fru ctose
Where is the anomeric carbon?
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HOCH2
5
O
H HO
H
OH ( )
2
CH2 OH
HO
H
1
 - D -Fru ctofu ran os e
(- D -Fructose)
20-17
20 Chair Conformations >> Haworth projected
anomeric
anomeric
carbon
carbon
CH
OH six-membered ring is more
CH
2 the
2 OH
• For pyranoses,
OO
HO
HO
HO
accuratelyHO
represented
OH()
OH()as a chair conformation.
OH
OH
 -D-D
-Glu
-Glucopyran
copyranososee
( (-D
-Glucos
-D
-Glucose)e)
anomeric
carbon
CH
CH22OH
OH
CH2 OH
HO
HO
OH
OH
O
HO
HO
HO
O
O
HO
OH()
CC
OH
OH
OH
HH
 -D -Glu copyran os e
-Glucosee
DD-Glucos
( - D -Glucos e)
CH2 OH
HO form
Most common
OH
HO vs axial
O
b/c OH in equatorial
C
(more stable)
OH H
The above
D -Glucos
e
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HO
HO
HO
HO
CH22OH
OH
O
O
HO
HO OH( )
OH( )
-- D -Glu copyran
copyranos
osee
(( 
--D
D -Glucose)
-Glucose)
CH2 OH
O
HO
OH( )
are in equilib. In aqueous
solut.
- D -Glu copyran os e
(  - D -Glucose)
20-18
20 Chair Conformations
• In both Haworth projections and chair conformations,
the orientations of groups on carbons 1- 5 of -Dglucopyranose are up, down, up, down, and up.
6
CH2 OH
5
O OH()
H
H
4 OH
1
H
HO
H
3
2
H OH
-D -Glucop yranose
(Haw orth p rojection)
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6
CH2 OH
4
HO
HO
O
5
3
2
OH 1
OH( )
 - D -Glucopyranose
(ch air con formation)
20-19
20 Mutarotation
•change in mea. specific rotation that accompanies the
equilibration of alpha and beta anomers in aqueous solution.
• e.g : -D-glucose or -D-glucose into H2O . . .
specific rotation of solution changes to an equilibrium
of +52.7°(64% beta & 36% alpha forms).
HO
HO
CH2 OH
O
OH
OH
-D -Glucopyranose
[] D 2 5 = + 18.7°
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HO
HO
CH2 OH
OH
O
C
HO
H
Open-chain form
HO
HO
CH2 OH
O
HO
OH
-D -Glucopyranose
[] D 2 5 = +112°
20-20
20 Physical Properties
• Monosaccharides are colorless crystalline solids,
very soluble in water, but only slightly soluble in
ethanol
• Sweetness relative to sucrose:
S w eetness
Relative to
Carbohydrate
S ucrose
fructos e
1.74
sucrose (tab le sugar) 1.00
honey
0.97
glu cose
0.74
maltose
0.33
galactos e
0.32
lactose (milk su gar)
0.16
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S w eetness
Relative to
Artificial
Sw eetener
S ucrose
saccharin
450
acesu lfame-K
200
aspartame
180
20-21
20 Formation of Glycosides
• Treatment of a monosaccharide, all of which exist
almost exclusively in cyclic hemiacetal forms,
with an alcohol gives an acetal.
anomeric
carbon
CH2 OH
O OH
H
+
H
H
+ CH3 OH
OH H
-H2 O
HO
H
glycos idic
H OH
CH2 OH
bond
-D -Glu copyran os e
O OCH3
H
(-D -Glu cose)
H
+
OH H
H
HO
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CH2 OH
OH
H
H
OH H
HO
OCH3
H OH
H OH
Methyl -D -glu copyran os ide Methyl -D -glu copyran os ide
(Methyl -D -glu coside)
(Methyl -D -glucos ide)
20-22
20 Formation of Glycosides
• A cyclic acetal derived from a monosaccharide is called
a glycoside.
• The bond from the anomeric carbon to the -OR group is
called a glycosidic bond.
• Mutarotation is not possible in a glycoside because an
acetal, unlike a hemiacetal, is not in equilibrium with
the open-chain carbonyl-containing compound.
• Glycosides are stable in water and aqueous base, but
like other acetals, are hydrolyzed in aqueous acid to an
alcohol and a monosaccharide.
• Glycosides are named by listing the alkyl or aryl group
bonded to oxygen followed by the name of the
carbohydrate in which the ending -e is replaced by -ide.
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20-23
20 Reduction to Alditols
• The carbonyl group of a monosaccharide can be
reduced to an hydroxyl group by a variety of
reducing agents, including NaBH4 and H2 in the
presence of a transition metal catalyst.
• The reduction product is called an alditol.
HO
HO
CH2 OH
O
OH
OH
-D -Glucop yranose
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CHO
H OH
HO H
NaBH4
H OH
H OH
CH2 OH
D -Glu cose
CH2 OH
H OH
HO H
H OH
H OH
CH2 OH
D -Glucitol
(D -Sorbitol)
20-24
20 Reduction to Alditols
• Sorbitol is found in the plant world in many berries and
in cherries, plums, pears, apples, seaweed, and algae.
• It is about 60 percent as sweet as sucrose (table sugar)
and is used in the manufacture of candies and as a
sugar substitute for diabetics.
• These three alditols are also common in the biological
world.
CH2 OH
CH2 OH
H
OH
H
OH
CH2 OH
Erythritol
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HO
HO
H
H
H
H
OH
OH
CH2 OH
D -Mannitol
CH2 OH
H
OH
HO
H
H
OH
CH2 OH
Xylitol
20-25
20 Oxidation to Aldonic Acids
• The aldehyde group of an aldose is oxidized under
basic conditions to a carboxylate anion.
• The oxidation product is called an aldonic acid.
• A carbohydrate that reacts with an oxidizing agent to
form an aldonic acid is classified as a reducing sugar
(it reduces the oxidizing agent).
O
H
C
HO
HO
CH2 OH
O
OH
- D-Glucopyranose
(- D-Glucose)
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OH
H
HO
H
H
OH oxidizing
agent
H
OH
basic
OH solution
CH2 OH
D-Glucose
O-
O
C
H
HO
H
H
OH
H
OH
OH
CH2 OH
D-Gluconate
20-26
20 Oxidation to Uronic Acids
• Enzyme-catalyzed oxidation of the primary
alcohol at C-6 of a hexose yields a uronic acid.
• Enzyme-catalyzed oxidation of D-glucose, for example,
yields D-glucuronic acid.
CHO
enzymeH
OH
catalyzed
HO
H
oxidation
H
OH
H
OH
CH2 OH
D-Glucose
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CHO
H
OH
COOH
O
HO
H
HO
H
OH
HO
OH
H
OH
COOH
D-Glucuronic acid
(a uronic acid)
OH
20-27
20 D-Glucuronic Acid
• D-Glucuronic acid is widely distributed in the plant and
animal world.
• In humans, it is an important component of the acidic
polysaccharides of connective tissues.
• It is used by the body to detoxify foreign phenols and
alcohols; in the liver, these compounds are converted
to glycosides of glucuronic acid and excreted in the
urine.
COOHO
HO
HO
O
O
OH
Propofol
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A u rin e-s olu ble glucuronide
20-28
20 Phosphate Esters
• Mono- and diphosphoric esters are intermediates
in the metabolism of monosaccharides.
• For example, the first step in glycolysis is conversion
of D-glucose to -D-glucose 6-phosphate.
• Note that at the pH of cellular and intercellular fluids,
both acidic protons of a diphosphoric ester are ionized,
giving it a charge of -2.
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CHO
H
OH
HO
H
H
OH
H
OH O
CH2 O-P- O OD-Glucose 6-phosphate
O
O P OO
CH2
HO
HO
O
HO
OH
-D-Glucose 6-phosphate
20-29
20 Disaccharides
• Sucrose (table sugar)
• Sucrose is the most abundant disaccharide in the
biological world; it is obtained principally from the juice
of sugar cane and sugar beets.
• Sucrose is a nonreducing sugar.
CH2 OH
O
OH
1
HO
HO
OH
HO
OH
O
O
HO 2
CH2 OH
1
OH
HOCH2
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a unit of -Dglucopyranose
CH2 OH
O
HOCH2
O
HO
1
O
2
-1,2-glycosidic bond
a unit of -Dfructofuranose
CH2 OH
OH
1
20-30
20 Disaccharides
• Lactose
• Lactose is the principal sugar present in milk; it makes
up about 5 to 8 percent of human milk and 4 to 6
percent of cow's milk.
• It consists of D-galactopyranose bonded by a -1,4glycosidic bond to carbon 4 of D-glucopyranose.
• Lactose is a reducing sugar.
CH2 OH
OH
O
CH2 OH
O
OH
4
1
OH
CH2 OH
-1,4-glycosid ic bond
O
4
O
OH
OH
OH
HO
1
OH
O
HO
CH2 OH
O
OH
OH
OH
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20-31
20 Disaccharides
• Maltose
• Present in malt, the juice from sprouted barley and
other cereal grains.
• Maltose consists of two units of D-glucopyranose
joined by an -1,4-glycosidic bond.
• Maltose is a reducing sugar.
1
HOCH2 O
HO
CH2 OH
4
O
OH
OH
HO
OH
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HO
O OH HO
-1,4-glycosidic
bond
CH2 OH
O
1
OH 4 CH2 OH
O
O
OH
HO
OH
20-32
20 Polysaccharides
• Polysaccharide: a carbohydrate consisting of
large numbers of monosaccharide units joined by
glycosidic bonds.
• Starch: a polymer of D-glucose.
• Starch can be separated into amylose and amylopectin.
• Amylose is composed of unbranched chains of up to
4000 D-glucose units joined by -1,4-glycosidic bonds.
• Amylopectin contains chains up to 10,000 D-glucose
units also joined by -1,4-glycosidic bonds; at branch
points, new chains of 24 to 30 units are started by 1,6-glycosidic bonds.
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20-33
20 Polysaccharides
• Figure 20.3 Amylopectin.
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20-34
20 Polysaccharides
• Glycogen is the energy-reserve carbohydrate for
animals.
• Glycogen is a branched polysaccharide of
approximately 106 glucose units joined by -1,4- and 1,6-glycosidic bonds.
• The total amount of glycogen in the body of a wellnourished adult human is about 350 g, divided almost
equally between liver and muscle.
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20-35
20 Polysaccharides
• Cellulose is a linear polysaccharide of D-glucose
units joined by -1,4-glycosidic bonds.
• It has an average molecular weight of 400,000 g/mol,
corresponding to approximately 2200 glucose units per
molecule.
• Cellulose molecules act like stiff rods and align
themselves side by side into well-organized waterinsoluble fibers in which the OH groups form numerous
intermolecular hydrogen bonds.
• This arrangement of parallel chains in bundles gives
cellulose fibers their high mechanical strength.
• It is also the reason why cellulose is insoluble in water.
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20-36
20 Polysaccharides
• Figure 20.4 Cellulose is a linear polymer
containing as many as 3000 units of D-glucose
joined by -1,4-glycosidic bonds.
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20-37
20 Polysaccharides
• Cellulose (cont’d)
• Humans and other animals cannot use cellulose as
food because our digestive systems do not contain glucosidases, enzymes that catalyze hydrolysis of glucosidic bonds.
• Instead, we have only -glucosidases; hence, the
polysaccharides we use as sources of glucose are
starch and glycogen.
• Many bacteria and microorganisms have glucosidases and can digest cellulose.
• Termites have such bacteria in their intestines and can
use wood as their principal food.
• Ruminants (cud-chewing animals) and horses can also
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digest grasses and hay.
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20 Acidic Polysaccharides
• Acidic polysaccharides: a group of
polysaccharides that contain carboxyl groups
and/or sulfuric ester groups, and play important
roles in the structure and function of connective
tissues.
• There is no single general type of connective tissue.
• Rather, there are a large number of highly specialized
forms, such as cartilage, bone, synovial fluid, skin,
tendons, blood vessels, intervertebral disks, and
cornea.
• Most connective tissues are made up of collagen, a
structural protein, in combination with a variety of
acidic polysaccharides.
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20 Acidic Polysaccharides
• Hyaluronic acid
• contains from 300 to 100,000 repeating units.
• is most abundant in embryonic tissues and in
specialized connective tissues such as synovial fluid,
the lubricant of joints in the body, and the vitreous of
the eye where it provides a clear, elastic gel that
maintains the retina in its proper position
D -glucu ronic acid
N-Acetyl-D -glu cosamine
-
4
HO
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COO
4
O HO
O
1
CH2 OH
O
1
NH
C
H3 C
O
The rep eating unit of h yalu ronic acid
3
OH
O
3
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20 Acidic Polysaccharides
• Heparin: a heterogeneous mixture of variably
sulfonated polysaccharide chains, ranging in
molecular weight from 6,000 to 30,000 g/mol.
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20 Acidic Polysaccharides
• Heparin (cont’d)
• Heparin is synthesized and stored in mast cells of
various tissues, particularly the liver, lungs, and gut.
• The best known and understood of its biological
functions is its anticoagulant activity.
• It binds strongly to antithrombin III, a plasma protein
involved in terminating the clotting process.
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20-42
20 Carbohydrates
End
Chapter 20
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20-43