Chemistry 121(01) Winter 2010-11
Introduction to Organic Chemistry and Biochemistry
Instructor Dr. Upali Siriwardane (Ph.D. Ohio State)
E-mail: upali@chem.latech.edu
Office: 311 Carson Taylor Hall ; Phone: 318-257-4941;
Office Hours: MWF 8:00 am - 10:00 am;
TT 9:00 – 10:00 am & 1:00-2:00 pm.
December 17, 2010 Test 1 (Chapters 12-13)
January 19, 2011 Test 2 (Chapters 14,15 & 16)
February 7, 2011 Test 3(Chapters 17, 18 & 19)
February 23, 2011 Test 4 (Chapters 20, 21 & 22)
February 24, 2011
Comprehensive Make Up Exam:
Chemistry 121, Winter 2011, LA Tech
18-1
Chapter 18:Carbohydrates
Chemistry 121, Winter 2011, LA Tech
18-2
Chapter 18: Carbohydrates
18.1 Biochemistry--An Overview
18.2 Occurrence and Functions of Carbohydrates
18.3 Classification of Carbohydrates
18.4 Chirality: Handedness in Molecules
18.5 Stereoisomerism: Enantiomers and Diastereomers
18.6 Designating Handedness Using Fischer Projections
18.7 Properties of Enantiomers
18.8 Classification of Monosaccharides
18.9 Biochemically Important Monosaccharides
18.10 Cyclic Forms of Monosaccharides
18.11 Haworth Projection Formulas
18.12 Reactions of Monosaccharides
18.13 Disaccharides
18.14 General Characteristics of Polysaccharides
18.15 Storage Polysaccharides
18.16 Structural Polysaccharides
18.17 Acidic Polysaccharides
18.18 Glycolipids and Glycoproteins
18.19 Dietary Considerations and Carbohydrates
Chemistry 121, Winter 2011, LA Tech
18-3
Biochemistry
Biochemistry is the study of the chemical processes in
living organisms. It deals with the structure and function
of cellular components, such as proteins, carbohydrates,
lipids, nucleic acids, and other biomolecules.
• Carbohydrates
• Lipids
• Proteins
• Nucleic Acids
• Use of carbohydrates as an energy source
Chemistry 121, Winter 2011, LA Tech
18-4
The Study of Living Things
Biochemistry is the study of the chemical
substances found in living organisms and the
chemical interactions of these substances with
each other.
A biochemical substance is a chemical substance
found within a living organism.
Two types of biochemical substances:
bioinorganic substances and bioorganic
substances.
• Bioinorganic substances : water and inorganic salts.
• Bioorganic substances : carbohydrates, lipids,
proteins, and nucleic acids
Chemistry 121, Winter 2011, LA Tech
18-5
Occurrence and Functions of Carbohydrates
“hydrates of carbon”: Cn (H2O)2
Occurrence
Different objects such as sheets of paper, insect skeletons,
fruits, cotton fabrics and ropes have one common feature:
they all contain carbohydrates.
Functions
The chemical structure of carbohydrates, with their many
hydroxyl groups and the ability to assume
various spatial configurations, makes it possible for them to
form nearly unlimited combinations
with other carbohydrate molecules, as well as with proteins
and lipids. The resulting structures
perform important biological functions.
Chemistry 121, Winter 2011, LA Tech
18-6
Classification of Carbohydrates
Monosaccharides
They consist of one sugar containing 3,4,5,6 and 7 carbon atoms and are
usually colorless, water-soluble, crystalline solids. Some
monosaccharides have a sweet taste. Examples of monosaccharides
include glucose (dextrose), fructose (levulose), galactose, xylose and
ribose.
Disaccharides
a sugar (a carbohydrate) composed of two monosaccharides.
Oligosaccharide
An oligosaccharide is a saccharide polymer containing a small number
(typically 3-10 monosaccharides
Polysacharides
Are relatively complex carbohydrates. They are polymers made up of
many monosaccharides joined together by glycosidic bonds. They
are insoluble in water, and have no sweet taste.
Chemistry 121, Winter 2011, LA Tech
18-7
Classification of Sugars
Number of carbon atoms
Triose sugar: three carbon atoms
Tetroses sugar: four carbon atoms
Pentoses sugar five carbon atoms
Hexoses sugar: six carbon atoms
Number fo units (Saccharide-sugar units)
Monosaccharide (one sugar unit);
Disaccharide (two sugar units);
Oligosaccharide (2 to 10 sugar units);
Polysaccharide (over 10 sugar units).
Chemistry 121, Winter 2011, LA Tech
18-8
Chirality: Handedness in Molecules
A "chiral" molecule is one that is not superimposable with its mirror image. Like left and right
hands that have a thumb, fingers in the same order, but are mirror images and not the same,
chiral molecules have the same things attached in the same order, but are mirror images and not
the same.
Chemistry 121, Winter 2011, LA Tech
18-9
Monosaccharides
Glyceraldehyde contains a stereocenter and exists
as a pair of enantiomers
CHO
CHO
H
C
OH
CH2 OH
(R)-Glyceraldehyde
Chemistry 121, Winter 2011, LA Tech
HO
C
H
CH2 OH
(S)-Glyceraldeh yd e
18-10
Fischer Projection Formulas
Fischer projection: a two dimensional
representation for showing the configuration of a
tetrahedral stereocenter
• horizontal lines represent bonds projecting forward
• vertical lines represent bonds projecting to the rear
• the first and last carbons in the chain are written in full;
others are indicated by the crossing of bonds
CHO
H
C
OH
CH2 OH
(R)-Glyceraldeh yd e
Chemistry 121, Winter 2011, LA Tech
con vert to
a Fischer
projection
CHO
H
OH
CH2 OH
(R)-Glyceraldeh yd e
18-11
Stereoisomerism: Enantiomers and Diastereomers
A Fischer projection is the most useful projection for
discovering enantiomers. Compare the Glyceraldehyde
enantiomer structures in this diagram.
D- and L-Monosaccharides
CHO
H
OH
CH2 OH
CHO
HO
H
CH2 OH
D -Gly ceraldehy de
L-Gl yceraldehy de
[]25
= +13.5°
D
[]25
= -13.5°
D
D-monosaccharide: a monosaccharide that, when written as a
Fischer projection, has the -OH on its penultimate carbon on the
right
L-monosaccharide: a monosaccharide that, when written as a
Fischer projection, has the -OH on its penultimate carbon on the
Chemistry 121, Winter 2011, LA Tech
18-12
left
Properties of Enantiomers
Enantiomers have, when present in a symmetric
environment, identical chemical and physical properties
except for their ability to rotate plane-polarized light by
equal amounts but in opposite directions.
A mixture of equal parts of an optically active isomer and
its enantiomer is termed racemic and has a net rotation of
plane-polarized light of zero.
Enantiomers of each other often do have different
chemical properties related to other substances that are
also enantiomers. Since many molecules in the bodies of
living beings are enantiomers themselves, there is often a
marked difference in the effects of two symmetrical
enantiomers on living beings, including human beings.
Chemistry 121, Winter 2011, LA Tech
18-13
Diastereomers
Have more than one chiral centers
Diastereomers (or diastereoisomers) are
stereoisomers that are not enantiomers (nonsuperposable mirror images of each other).
Diastereomers can have different physical
properties and different reactivity. In another
definition diastereomers are pairs of isomers that
have opposite configurations at one or more of
the chiral centers but are not mirror images of
each other.
Chemistry 121, Winter 2011, LA Tech
18-14
Diastereomers of Tartaric acid
Tartaric acid contains two asymmetric centers, but two of the "isomers"
are equivalent and together are called a meso compound. This
configuration is not optically active, while the remaining two isomers
are D- and L- mirror images, i.e., enantiomers. The meso form is a
diastereomer of the other forms.
Chemistry 121, Winter 2011, LA Tech
18-15
What is Plane Polarized Light?
Chemistry 121, Winter 2011, LA Tech
18-16
Optically active of enantiomers
CHO
H
OH
CH2 OH
CHO
HO
H
CH2 OH
D -Gly ceraldehy de
L-Gl yceraldehy de
[]25
= +13.5°
D
[]25
= -13.5°
D
Chemistry 121, Winter 2011, LA Tech
18-17
D- and L-Monosaccharides
In 1891, Emil Fischer made the arbitrary
assignments of D- and L- to the enantiomers of
glyceraldehyde
CHO
H
OH
CH2 OH
CHO
HO
H
CH2 OH
D -Gly ceraldehy de
L-Gl yceraldehy de
[]25
= +13.5°
D
[]25
= -13.5°
D
Chemistry 121, Winter 2011, LA Tech
18-18
Functional Groups
Aldoses:
Monosaccarides with aldehyde functional
group. E.g. D-glucose
Ketoses:
Monosaccarides with keto functional
group. E.g. D-fructose
Chemistry 121, Winter 2011, LA Tech
18-19
Aldoses
Chemistry 121, Winter 2011, LA Tech
18-20
Aldoses
Hexoses
Chemistry 121, Winter 2011, LA Tech
18-21
Cyclization of D-glucose
CH
 -D - glucose
OH
2
H
O
H
H
H
C
OH
OH
H
C
OH
HO
C
H
H
C
OH
H
C
OH
CH
H
OH
O
2
OH
H
CH
2
 - D - glucose
OH
O
H
H
OH
OH
H
OH
H
H
Chemistry 121, Winter 2011, LA Tech
OH
OH
18-22
Fischer & Haworth Projection
In solutions less than 1% of a sugar will be in the
linear form shown as Fischer projection
The normal form of most sugars is in a cyclic
hemiacetal form shown as Haworth projection
Chemistry 121, Winter 2011, LA Tech
18-23
Converting Fischer to Haworth
Projection
Chemistry 121, Winter 2011, LA Tech
18-24
-Cyclic form of Gulose
Chemistry 121, Winter 2011, LA Tech
18-25
Aldopentoses
Chemistry 121, Winter 2011, LA Tech
18-26
Chemistry 121, Winter 2011, LA Tech
18-27
Two monsaccharides connected by a bridging O atom called a
glycosidic bond as in sucrose.
Chemistry 121, Winter 2011, LA Tech
18-28
D- and L-Monosaccharides
According to the conventions proposed by Fischer
• D-monosaccharide: a monosaccharide that, when
written as a Fischer projection, has the -OH on its
penultimate carbon on the right
• L-monosaccharide: a monosaccharide that, when
written as a Fischer projection, has the -OH on its
penultimate carbon on the left
Chemistry 121, Winter 2011, LA Tech
18-29
D- and L-Monosaccharides
Following are
• the two most common D-aldotetroses and
• the two most common D-aldopentoses
CHO
CHO
H
OH
H
OH
CHO
HO
H
H
OH
CH2 OH
D-Erythrose
CH2 OH
D-Threose
Chemistry 121, Winter 2011, LA Tech
H
H
H
OH
OH
OH
CH2 OH
D-Ribose
CHO
H
H
H
H
OH
OH
CH2 OH
2-Deoxy-Dribose
18-30
D- and L-Monosaccharides
• and the three common D-aldohexoses
CHO
H
OH
HO
H
H
H
OH
OH
CH2 OH
D-Glucose
Chemistry 121, Winter 2011, LA Tech
CHO
H
OH
HO
H
HO
H
CHO
H
N H2
HO
H
H
H
OH
CH2 OH
H
D-Galactose
OH
OH
CH2 OH
D-Glucosamine
18-31
D- and L-Monosaccharides
Amino sugars
H
HO
H
H
CHO
NH2
H
OH
OH
CH2 OH
H2 N
HO
H
H
CHO
2
H
H
OH
OH
CH2 OH
CHO
H
NH2
HO
H
HO 4 H
H
OH
CH2 OH
D -Gl ucosami ne D -M an nosamin e
D -G al actosami ne
(C-2 stereoi somer (C-4 stereo iso mer
o f D -g luco sami ne) o f D -g luco sami ne)
H
HO
H
H
CHO O
NHCCH3
H
OH
OH
CH2 OH
N -A cetyl -D g luco samine
• N-acetyl-D-glucosamine is a component of many
polysaccharides, including connective tissue such as
cartilage; it is also a component of chitin, the hard
shell-like exoskeleton of lobsters, crabs, and shrimp
Chemistry 121, Winter 2011, LA Tech
18-32
Classification of Monosaccharides
Monosaccharides have the general formula CnH2nOn
the most common have from 3 to 9 carbons
Triose (3) , tetrose(4), pentose(5), hexose(6)
• aldose: a monosaccharide containing an aldehyde
group: E.g. D-glucose
• ketose: a monosaccharide containing a ketone group:
E.g. D-Fructose
Chemistry 121, Winter 2011, LA Tech
18-33
Carbohydrates: Monosaccharides
Carbohydrate: a polyhydroxy aldehyde, a polyhydroxy
ketone, or a polymeric substance that gives these
compounds on hydrolysis
Monosaccharide: a carbohydrate that cannot be hydrolyzed
to a simpler carbohydrate
• monosaccharides have the general formula CnH2nOn
• the most common have from 3 to 9 carbons
• aldose: a monosaccharide containing an aldehyde
group: E.g. D-glucose
• ketose: a monosaccharide containing a ketone group:
E.g. D-Fructose
Chemistry 121, Winter 2011, LA Tech
18-34
Monosaccharides
• monosaccharides are classified by their number of
carbon atoms
Name
trios e
tetrose
pentose
Chemistry 121, Winter 2011, LA Tech
Formula
C3 H6 O3
C4 H8 O4
hexose
C5 H10 O5
C6 H12 O6
heptose
octose
C7 H14 O7
C8 H16 O8
18-35
Aldoses: Trioses, Tetroses and Pentoses
Chemistry 121, Winter 2011, LA Tech
18-36
Aldoses: Hexoses
Chemistry 121, Winter 2011, LA Tech
18-37
Important ketoses:
pentoses
Chemistry 121, Winter 2011, LA Tech
hexose
heptoses
18-38
Monosaccharides
• there are only two trioses
CHO
CH2 OH
CHOH
C=O
CH2 OH
Glycerald ehyde
(an aldotrios e)
CH2 OH
D ihydroxyacetone
(a ketotriose)
• often aldo- and keto- are omitted and these compounds
are referred to simply as trioses
• although this designation does not tell the nature of the
carbonyl group, it at least tells the number of carbons
Chemistry 121, Winter 2011, LA Tech
18-39
Biochemically Important Monosaccharides
• Glucose is the most common monosaccharide consumed
and is the circulating sugar of the bloodstream.
-Insulin and glucagon regulate blood levels of glucose.
• Galactose, a component of lactose (milk sugar) is also
found in some plant gums and pectins.
-Galactosemia results from inability to metabolize galactose.
-If treated, galactosemia can be managed medically.
Untreated galactosemia may result in mental retardation,
liver damage, or death.
• Fructose is slightly sweeter than glucose. It is an
intermediary in metabolism and is found in many fruits.
• Ribose and deoxyribose are aldopentose components of
DNA and RNA.
Chemistry 121, Winter 2011, LA Tech
18-40
Cyclic Forms of Monosaccharides
Intramolecular cyclization of simple sugars tend to exist
primarily in cyclic form through hemiacetal or hemiketal
formation. It is the most stable arrangement.
CH2OH
C
CH2OH
H
OH
C
C
C
C
aldehyde
Chemistry 121, Winter 2011, LA Tech
C
O
O
C
C
C
C
hemiacetal
18-41
OH
 - and  - anomers
The -OH group that forms can be above or
below the ring resulting in two forms anomers
 and  are used to identify the two forms.
 - OH group is down compared to CH2OH
(trans).
 - OH group is up compared to CH2OH (cis).
Chemistry 121, Winter 2011, LA Tech
18-42
 - and  forms of D-glucose
 -D - glucose
CH 2 OH
H
O
H
H
OH
O
H
C
H
OH
OH
H
C
OH
HO
C
H
H
C
OH
H
C
OH
OH
H
 - D - glucose
CH 2 OH
O
H
H
CH 2 OH
OH
H
OH
Chemistry 121, Winter 2011, LA Tech
OH
H
H
OH
18-43
Haworth Projection Formulas
• the anomers of D-glucopyranose
1
CHO
H
OH
HO
H
H
H
red raw to sh ow th e -OH
on carbon-5 close to the
aldeh yd e on carbon-1
OH
5
CH2 OH
OH
H5
O
H
OH H C
1 H
HO
OH
H
CH2 OH
D -Glucose
anomeric
carbon
CH2 OH
O
H
OH (  )
H
OH H
HO
H
H OH
-D -Glucopyranose
(-D -Glucose)
Chemistry 121, Winter 2011, LA Tech
OH
anomeric
carb on
CH2 OH
O
H
H
H
+
OH H
HO
OH(  )
H OH
-D -Glucopyranose
( -D -Glucos e )
18-44
Converting Fischer to Haworth
Projection
Chemistry 121, Winter 2011, LA Tech
18-45
Haworth Projections
• 5- and 6-membered hemiacetals are represented as
planar pentagons or hexagons viewed through the
edge
• most commonly written with the anomeric carbon on
the right and the hemiacetal oxygen to the back right
• - means that -OH on the anomeric carbon is cis to the
terminal -CH2OH; - means it is trans
• a 6-membered hemiacetal is shown by the infix -pyran• a 5-membered hemiacetal is shown by the infix -furan-
O
Furan
Chemistry 121, Winter 2011, LA Tech
O
Pyran
18-46
Cyclic Structures in Haworth Projections
Aldopentoses also form cyclic hemiacetals
• the most prevalent forms of D-ribose and other
pentoses in the biological world are furanoses
HOCH2
H
H
O
H
OH ( )
OH
OH
-D -Rib ofuranose
(-D -Ribose)
H
HOCH2
H
H
OH ( )
O
H
H
OH
H
-2-D eoxy-D -ribofu ran os e
(-2-D eoxy-D -ribose)
• the prefix deoxy- means “without oxygen”
Chemistry 121, Winter 2011, LA Tech
18-47
Cyclic Structures
D-Fructose, a 2-ketohexose, also forms a cyclic
hemiacetal
HOCH2
5
1
O
H HO
H
CH2 OH
2
OH ()
HO
H
- D -Fructofuranose
(- D -Fru ctose)
1
HOCH2
5
OH
H HO
CH2 OH
2
O
H
H
HO
HOCH2
5
O
H HO
OH ()
2
H
CH2 OH
1
H
anomeric
HO
carbon
 -D -Fructofu ran os e
( - D -Fructose)
Chemistry 121, Winter 2011, LA Tech
18-48
Fischer & Haworth Projection
In solutions less than 1% of a sugar will be in the
linear form shown as Fischer projection
The normal form of most sugars is in a cyclic
hemiacetal form shown as Haworth projection
Chemistry 121, Winter 2011, LA Tech
18-49
-Cyclic form of Gulose
Chemistry 121, Winter 2011, LA Tech
18-50
Aldopentoses
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18-51
Aldoxeoses
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18-52
Reactions of Monosaccharides
Reduction: The carbonyl group of a monosaccharide can be
reduced to an hydroxyl group by a variety of reducing
agents, including NaBH4
Oxidation: The -CHO group can be oxidized to –COOH
Reducing sugar: any carbohydrate that reacts with an
oxidizing agent to form an aldonic acid
Oxidation: OH to –COOH
Enzyme-catalyzed oxidation of the 1° alcohol at carbon-6 of
a hexose gives a uronic acid
Glucose Assay: The analytical procedure most often
performed in the clinical chemistry laboratory is the
determination of glucose in blood, urine, or other
biological fluid
Chemistry 121, Winter 2011, LA Tech
18-53
Reduction to Alditols
The carbonyl group of a monosaccharide can be
reduced to an hydroxyl group by a variety of
reducing agents, including NaBH4
Chemistry 121, Winter 2011, LA Tech
18-54
Reduction to Alditols
• name alditols by replacing the -ose of the name of the
monosaccharide by -itol
• sorbitol is found in the plant world in many berries and
in cherries, plums, pears, apples, and seaweed; it is
about 60% as sweet as sugar
• other common alditols include
CH2 OH
H
OH
H
OH
CH2 OH
Eryth ritol
Chemistry 121, Winter 2011, LA Tech
CH2 OH
HO
H
HO
H
H
OH
H
OH
CH2 OH
D -Mann itol
CH2 OH
H
OH
HO
H
H
OH
CH2 OH
Xylitol
18-55
Oxidation to Aldonic Acids
The -CHO group can be oxidized to -COOH
• reducing sugar: any carbohydrate that reacts with an
oxidizing agent to form an aldonic acid
Chemistry 121, Winter 2011, LA Tech
18-56
Oxidation to Uronic Acids
Enzyme-catalyzed oxidation of the 1° alcohol at
carbon-6 of a hexose gives a uronic acid
Chemistry 121, Winter 2011, LA Tech
18-57
Oxidation to Uronic Acids
• the body uses glucuronic acid to detoxify foreign
alcohols and phenols
• these compounds are converted in the liver to
glycosides of glucuronic acid and then excreted in the
urine
• the intravenous anesthetic propofol is converted to the
following water-soluble glucuronide and excreted
-
COO
HO
HO
HO
O
O
OH
Prop ofol
Chemistry 121, Winter 2011, LA Tech
A u rin e-soluble glucuron ide
18-58
Glucose Assay
The analytical procedure most often performed in
the clinical chemistry laboratory is the
determination of glucose in blood, urine, or other
biological fluid
• this need arises because of the high incidence of
diabetes in the population
Chemistry 121, Winter 2011, LA Tech
18-59
Glucose Assay
The glucose oxidase method is completely specific
for D-glucose
HO
HO
CH 2 OH
O
OH
 - D-Glucopyranose
OH
glucos e
+ O2 + H 2 O oxidase
H 2 O2
Hydrogen
peroxide
+
H
HO
H
H
CO2 H
OH
H
OH
OH
CH 2 OH
D-Gluconic acid
Chemistry 121, Winter 2011, LA Tech
18-60
Glucose Assay
• O2 is reduced to hydrogen peroxide, H2O2
• the concentration of H2O2 is proportional to the
concentration of glucose in the sample
• in one procedure, hydrogen peroxide is used to oxidize
o-toluidine to a colored product, whose concentration
is determined spectrophotometrically
NH2
CH3
+
H2 O2
peroxid ase
colored p rodu ct
2-Meth ylan iline
(o-Tolu idin e)
Chemistry 121, Winter 2011, LA Tech
18-61
Ascorbic Acid (Vitamin C)
L-Ascorbic acid (vitamin C) is synthesized both
biochemically and industrially from D-glucose
CHO
H
OH
HO
H
H
OH
H
OH
CH 2 OH
D -Glucos e
Chemistry 121, Winter 2011, LA Tech
both bioch emial
and in dus trial
synth eses
CH2 OH
H
OH O
H
HO
O
OH
L-A scorbic acid
(Vitamin C)
18-62
Ascorbic Acid (Vitamin C)
• L-ascorbic acid is very easily oxidized to Ldehydroascorbic acid
• both compounds are physiologically active and are
found in most body fluids
CH2 OH
H
CH 2 OH
OH O
O
H
HO
red uction
OH
L-A scorbic acid
(Vitamin C)
Chemistry 121, Winter 2011, LA Tech
oxid ation
H
OH O
O
H
O
O
L-D eh yd roascorbic acid
18-63
Disaccharides
A disaccharide forms by reaction of the -OH group on the
anomeric carbon of one monosaccharide with an –OH
group of a second monosaccharide.
• The linkage between monosaccharides in a disaccharide is
referred to as a glycosidic linkage and is named
according to the number of the carbon at which the
linkage begins and the carbon on the second
monosaccharide at which the linkage ends.
-The glycosidic linkage is also designated  or β, depending
upon whether the conformation at the anomeric carbon is
up or down.
Chemistry 121, Winter 2011, LA Tech
18-64
Disaccharides
Two monsaccharides connected by a bridging O atom called a glycosidic
bond as in sucrose.
Chemistry 121, Winter 2011, LA Tech
18-65
Sucrose
Table sugar, obtained from the juice of sugar cane
and sugar beet
Chemistry 121, Winter 2011, LA Tech
18-66
Lactose
The principle sugar present in milk
• about 5 - 8% in human milk, 4 - 5% in cow’s milk
Chemistry 121, Winter 2011, LA Tech
18-67
Maltose
From malt, the juice of sprouted barley and other
cereal grains
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18-68
Polysaccharides
Uses for polysaccharides
• Storage polysaccharides
Energy storage - starch and glycogen
• Structural polysaccharides
Used to provide protective walls or lubricative
coating to cells - cellulose and
mucopolysaccharides.
• Structural peptidoglycans
• Bacterial cell walls
Chemistry 121, Winter 2011, LA Tech
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Starch
Starch is used for energy storage in plants
• it can be separated into two fractions; amylose and
amylopectin
• amylose is composed of unbranched chains of up to
4000 D-glucose units joined by -1,4-glycosidic bonds
• amylopectin is a highly branched polymer of Dglucose; chains consist of 24-30 units of D-glucose
joined by -1,4-glycosidic bonds and branches created
by -1,6-glycosidic bonds
Chemistry 121, Winter 2011, LA Tech
18-70
Starch
• at the cellular level, the biochemical basis for this
classification is a group of relatively small membranebound carbohydrates
Chemistry 121, Winter 2011, LA Tech
18-71
Amylose starch
•
Straight chain that forms coils  (1
CH2OH
O
O
H
HOH2C
HO
O
HOH2C
O
H
OH
HO
H
OH
H
OH
H
H
OH
O
4) linkage.
CH2OH
O
OH
H
HO
O
H
CH2OH
O
OH
H
O
H
HO
O
O
O H
HOH2C
HO
OH
H
Chemistry 121, Winter 2011, LA Tech
H
HO
OH
CH2OH
H O
O
18-72
Glycogen
• Energy storage of animals.
• Stored in liver and muscles as granules.
• Similar to amylopectin but more highly
branched.
O
 (1
O
6) linkage
at crosslink
O
O
O
c
O
O
O
c
O
O
O
O
O
O
Chemistry 121, Winter 2011, LA Tech
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Glycogen
The reserve carbohydrate for animals
• a nonlinear polymer of D-glucose units joined by -1,4and -1,6-glycosidic bonds
• the total amount of glycogen in the body of a wellnourished adult is about 350 g (about 3/4 of a pound)
divided almost equally between liver and muscle
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Structural Polysaccharides: Cellulose
•
CH2OH
OH
Most abundant polysaccharide.
 (1
4) glycosidic linkages.
Result in long fibers - for plant structure.
H
O
H
O
•
•
HO
OH
H
O
H
OH
CH2OH
CH2OH
Chemistry 121, Winter 2011, LA Tech
OH
H
O
H
O
HO
OH
H
O
O
H
OH
CH2OH
CH2OH
OH
H
O
H
O
HO
OH
H
O
O
H
OH
CH2OH
18-75
Cellulose
Cellulose is a linear polymer of D-glucose units
joined by -1,4-glycosidic bonds
• it has an average molecular weight of 400,000,
corresponding to approximately 2800 D-glucose units
per molecule
• both rayon and acetate rayon are made from
chemically modified cellulose
Chemistry 121, Winter 2011, LA Tech
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Mucopolysaccharides: lubricative coatings
• These materials provide a thin, viscous, jellylike coating to cells.
• The most abundant form is
hyaluronic acid.
H
CH2OH
O
H
4)
COO
H
(1
3)
H
CH2OH
O
OH
O
H
H
O
HO
H
H
H
NH
C O
CH3
HO
H
H
H
H
•
O
O
H
COO-
OH
O
H
-
O
H
OH
O
H
COOH
O
HO
O
H
(1
CH2OH
O
H
H
H
H
H
NH
C O
CH3
OH
NH
C O
CH3
OH
Alternating units of N-acetylglucosamine
and D-glucuronic acid.
OH
Chemistry 121, Winter 2011, LA Tech
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Glycolipids and Glycoproteins
Glycolipids: are carbohydrate-attached lipids. Their role is
to provide energy and also serve as markers for cellular
recognition.
Glycoproteins: are the proteins covalently attached to
carbohydrates such as glucose, galactose, lactose,
fucose, sialic acid, N-acetylglucosamine, Nacetylgalactosamine, etc.
The antigens which determine blood types belong to
glycoproteins and glycolipids (more info later).
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Cyclic Structure
Monosaccharides have hydroxyl and carbonyl
groups in the same molecule and exist almost
entirely as five- and six-membered cyclic
hemiacetals
• anomeric carbon: the hemiacetal carbon of a cyclic
form of a monosaccharide
• anomers: monosaccharides that differ in configuration
only at their anomeric carbons
Chemistry 121, Winter 2011, LA Tech
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Glycosides
Glycoside: a carbohydrate in which the -OH on its
anomeric carbon is replaced by -OR
anomeric
carbon
CH2 OH
O OH
H
+
H
H
+ CH3 OH
OH H
-H2 O
HO
H
H OH
-D -Glu copyran os e
(-D -Glu cose)
glycos idic
bond
CH2 OH glycos idic
bond
O
H
H
H
+
OH H
HO
OCH 3
H OH
H OH
Methyl -D -glu copyran os ide Methyl -D -glu copyran os ide
(Methyl -D -glu coside)
(Methyl -D -glucos ide)
Chemistry 121, Winter 2011, LA Tech
CH2 OH
O OCH 3
H
H
OH H
H
HO
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Glycosides
Glycosidic bond: the bond from the anomeric
carbon of the glycoside to an -OR group
To name a glycoside, name the alkyl or aryl group
bonded to oxygen followed by the name of the
carbohydrate; replace the ending -e by -ide
• methyl -D-glucopyranoside
• methyl -D-ribofuranoside
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N-Glycosides
• the anomeric carbon of a cyclic hemiacetal also reacts
with an N-H of an amine to form an N-glycoside
• especially important in the biological world are the Nglycosides of D-Ribose and 2-deoxy-D-ribose with the
following heterocyclic aromatic amines
O
NH2
HN
O
N
H
Uracil
O
N
O
N
H
Cytosin e
HN
O
Pyrimidine b ases
Chemistry 121, Winter 2011, LA Tech
N
H
Thymine
NH2
CH3
O
N
N
N
H
Aden in e
N
N
HN
H2 N
N
N
H
Gu anine
Purine bas es
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N-Glycosides
• following is the -N-glycoside formed between Dribofuranose and cytosine
NH2
N
O
HOCH2
O
H
H
Chemistry 121, Winter 2011, LA Tech
N
a -N -glycosid ic
bond
H
H
HO
OH
anomeric
carbon
18-83
Blood Group Substances
Membranes of animal plasma cells have large
numbers of relatively small carbohydrates
• these membrane-bound carbohydrates are part of the
mechanism by which cell types recognize each other;
they act as antigenic determinants
• among the first discovered of these antigenic
determinants are the blood group substances
In the ABO system, individuals are classified
according to four blood types: A, B, AB, and O
Chemistry 121, Winter 2011, LA Tech
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Blood Group Substances
• one of these membrane-bound monosaccharides is Lfucose
An L-mon os acch arid e;
this -OH is on the left in
the Fischer projection
HO
H
H
HO
CHO
H
OH
Carbon 6 is -CH 3 rath er
OH rath er th an -CH OH
2
H
CH3
L-Fucose
Chemistry 121, Winter 2011, LA Tech
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Blood Group Substances
A, B, AB, and O blood types
Type A N -Acetyl-D galactos amin e
(-1,4)
D -Galactose
(-1,2)
(-1,3)
N-Acetyl-D glu cosamine
Red
blood
cell
N-Acetyl-D glu cosamine
Red
blood
cell
L-Fucose
Type B
D -galactos e
(-1,4)
D -Galactose
(-1,2)
(-1,3)
L-Fucose
Type O
(-1,3) N-Acetyl-D D -Galactose
glu cosamine
(-1,2)
Red
blood
cell
L-Fucose
Chemistry 121, Winter 2011, LA Tech
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Polysaccharides
• These are biopolymers composed of
hundreds to thousands of simple
sugar units (monosaccharides).
O
H
C
• The most common
monosaccharide used
H
C
OH
HO
C
H
H
C
OH
C
OH
in polysaccharides is glucose.
H
CH
Chemistry 121, Winter 2011, LA Tech
2
OH
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Polysaccharides
•
•
•
•
Uses for polysaccharides
Storage polysaccharides
Energy storage - starch and glycogen
•
Structural polysaccharides
Used to provide protective walls or
lubricative coating to cells - cellulose and
mucopolysaccharides.
• Structural peptidoglycans
• Bacterial cell walls
Chemistry 121, Winter 2011, LA Tech
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Starch
•
•
•
•
•
Energy storage used by plants
Long repeating chain of -D-glucose
• Chains up to 4000 units
Amylose
straight chain
Amylopectin branched structure
Starch is a mixture of about 75% amylopectin and 25%
amylose.
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Amylose starch
• Straight chain that forms coils  (1
linkage.
CH2OH
O
O
H
HOH2C
HO
O
HOH2C
O
H
OH
HO
H
OH
H
OH
H
H
OH
O
4)
CH2OH
O
OH
H
HO
O
H
CH2OH
O
OH
H
O
H
HO
O
O
O H
HOH2C
HO
OH
H
Chemistry 121, Winter 2011, LA Tech
H
HO
OH
CH2OH
H O
O
18-90
Amylose starch
Example showing coiled structure
- 12 glucose units
- hydrogens and side chains are omitted.
Chemistry 121, Winter 2011, LA Tech
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Amylopectin starch
• Amylopectin differs from amylose only in that it has
side chains. These are formed from
  (1
6) links
• Side chains occur every 24-30 units.
• Starch is stored as starch grains. They cannot
diffuse from the cell and have little effect on the
osmotic pressure of the cell.
Chemistry 121, Winter 2011, LA Tech
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Glycogen
• Energy storage of animals.
• Stored in liver and muscles as granules.
• Similar to amylopectin but more highly
branched.
O
 (1
O
6) linkage
at crosslink
O
O
O
c
O
O
O
c
O
O
O
O
O
O
Chemistry 121, Winter 2011, LA Tech
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Cellulose
• Most abundant polysaccharide.
•  (1
4) glycosidic linkages.
• Result in long fibers - for plant
structure.
CH2OH
OH
H
O
H
O
HO
OH
H
O
H
OH
CH2OH
CH2OH
Chemistry 121, Winter 2011, LA Tech
OH
H
O
H
O
HO
OH
H
O
O
H
OH
CH2OH
CH2OH
OH
H
O
H
O
HO
OH
H
O
O
H
OH
CH2OH
18-94
Mucopolysaccharides
• These materials provide a thin, viscous, jelly-like
coating to cells.
• The most abundant form is hyaluronic acid.
H
CH2OH
O
O
H
OH
O
H
COO-
H
•
(1
COO
H
(1
3)
H
•
H
•
COOO
HO
H
H
H
HO
H
H
H
H
NH
C O
CH3
O
O
H
OH
O
H
OH
O
H
-
O
HO
O
H
4)
CH2OH
O
CH2OH
O
H
H
H
H
H
H
NH
C O
CH3
OH
NH
C O
CH3
• Alternating units of
N-acetylglucosamine
and D-glucuronic acid.
OH
OH
Chemistry 121, Winter 2011, LA Tech
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Reducing and Nonreducing sugar.
Monosaccharides both aldoses and ketoses
Disaccharides with free hemiacetal or hemiketal
ends:maltose and lactose
Aldoses
Aldehyde sugars should show positive test for the
Benedict's test
Ketoses
give a positive test for Benedict's test because of
the ability of ketoses to get converted to aldoses
(aldehydes) via enediol.
Chemistry 121, Winter 2011, LA Tech
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Enediol Intermediate
Chemistry 121, Winter 2011, LA Tech
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Galactosemia and Lactose
Intolerance.
Galactosemia
Lack of enzymes necessary for the
conversion of galactose to phosphorylated
glucose which is used in the cellular
metabolism or glycolysis
Lactose Intolerance.
Lack of diagestive enzyme, lactase to
break down lactose to glucose and
galactose
Chemistry 121, Winter 2011, LA Tech
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Practice Exercise
Chemistry 121, Winter 2011, LA Tech
Answers:
a. Not a chiral center
b. Not a chiral center
c. Chiral center
d. Not a chiral center
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Exercise
Chemistry 121, Winter 2011, LA Tech
18-100
Interactions Between Chiral
Compounds
Our body responds differently to different
enantiomers:
One may give higher rate or one may be
inactive
• Example: Body response to D form of hormone
epinephrine is 20 times greater than its L isomer
Chemistry 121, Winter 2011, LA Tech
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Exercise
Chemistry 121, Winter 2011, LA Tech
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Cyclic Hemiacetal Forms of D-Glucose
Dominant form of monosaccharides with 5 or more C atoms is
cyclic - cyclic forms are in equilibrium with open chain form
Cyclic forms are formed by the reaction of carbonyl group
(C=O) with hydroxyl (-OH) group on carbon 5
Chemistry 121, Winter 2011, LA Tech
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Practice Exercise
Which of the monosaccharides glucose, fructose, galactose, and
ribose has each of the following structural characteristics?
(There may be more than one correct answer for a given
characteristic)
a. It is a pentose.
b. It is a ketose.
c. Its cyclic form has a 6-membered ring.
d. Its cyclic form has two carbon atoms outside the ring.
Answers:
a. Ribose
b. Fructose
c. Glucose, galactose
d. Fructose
Chemistry 121, Winter 2011, LA Tech
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Five important reactions of monosaccharides:
•
•
•
•
•
Oxidation to acidic sugars
Reduction to sugar alcohols
Glycoside formation
Phosphate ester formation
Amino sugar formation
These reactions will be considered with
respect to glucose.
Other aldoses, as well as ketoses, undergo
similar reactions.
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Oxidation
Oxidation to acidic functional groups present in
sugars: The redox chemistry of
monosaccharides is closely linked to the
alcohol and aldehyde
Oxidation can yield three different types of acidic
sugars depending on the type of oxidizing
agent used:
• Weak oxidizing agents such as Tollens and
Benedict’s solutions oxidize the aldehyde
end to give an aldonic acid.
• A reducing sugar is a carbohydrate that
gives a positive test with Tollens and
Benedict’s solutions.
Chemistry 121, Winter 2011, LA Tech
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Oxidizing Agents
Strong oxidizing agents can oxidize both ends
of a monosaccharide at the same time (the
carbonyl group and the terminal primary
alcohol group) to produce a dicarboxylic
acid:
• Such polyhydroxy dicarboxylic acids are known
as aldaric acids.
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Oxidization
In biochemical systems enzymes can oxidize
the primary alcohol end of an aldose such as
glucose, without oxidation of the aldehyde
group, to produce an alduronic acid.
Chemistry 121, Winter 2011, LA Tech
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Amino Sugar Formation
Amino sugar formation: An amino sugar - one
of the hydroxyl groups of a monosaccharide
is replaced with an amino group
In naturally occurring amino sugars the carbon
2 hydroxyl group is replaced by an amino
group
Amino sugars and their N-acetyl derivatives
are important building blocks of
polysaccharides such as chitin
Chemistry 121, Winter 2011, LA Tech
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Cellobiose
Cellobiose is produced as an intermediate in
the hydrolysis of the polysaccharide
cellulose:
• Cellobiose contains two b - D-glucose
monosaccharide units linked through a b (1—4)
glycosidic linkage.
CH2OH
 (1-4)
CH2OH
O
O
O
OH
H
OH
OH
OH
OH
OH
Cellobiose
Chemistry 121, Winter 2011, LA Tech
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Chitin
• Similar to cellulose in both function and structure
• Linear polymer with all b (14) glycosidic linkages - it has a
N-acetyl amino derivative of glucose
• Function is to give rigidity to the exoskeleton s of crabs,
lobsters, shrimp, insects, and other arthropods
HO
O
HO
HO
O
O
OH
HN
O
OH
O
HN
HN
HN
O
OH
O
O
OH
O
HO
O
O
O
N-Acetyl
-D-Glucoseamine
O
Chemistry 121, Winter 2011, LA Tech
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Acidic polysaccharides - polysaccharides with a repeating
disaccharide unit containing an amino sugar and a sugar with a
negative charge due to a sulfate or a carboxyl group.
Structural polysaccharide present in connective tissue associated
with joints, cartilage, synovial fluids in animals and humans
• Primary function is lubrication necessary for joint
movement
• These are heteropolysaccharides - have more than one type
of monosaccharide monomers is present.
Examples:
• Hyaluronic acid
• Heparin
Chemistry 121, Winter 2011, LA Tech
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Hyaluronic Acid and Heparin
Hyaluronic acid:
• Alternating residues of Nacetyl-b-D-glucosamine
and D-glucuronic acid.
• Highly viscous - serve as
lubricants in the fluid of
joints and part vitreous
humor of the eye.
Heparin:
• An anticoagulant-prevents
blood clots.
• Polysaccharide with 15–
90 disaccharide residues
per chain.
Chemistry 121, Winter 2011, LA Tech
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A glycolipid is a lipid molecule that has one or
more carbohydrate (or carbohydrate
derivative) units covalently bonded to it.
A glycoprotein is a protein molecule that has
one or more carbohydrate (or carbohydrate
derivative) units covalently bonded to it.
Chemistry 121, Winter 2011, LA Tech
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Nutrition
Foods high in carbs content constitute over 50% of the diet of
most people of the world -- a balanced dietary food should
contain about 60% of carbohydrate:
• Corn in South America
• Rice in Asia
• Starchy root vegetables in parts of Africa
• Potato and wheat in North America
Nutritionist divide dietary carbs into two classes:
• Simple carb: dietary monosaccharides or disaccharides sweet to taste commonly referred to as sugars - 20 % of the
energy in the US die
• Complex carbs: Dietary polysaccharides -- starch and
cellulose - normally not sweet to taste
Chemistry 121, Winter 2011, LA Tech
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Glycemic Foods
A developing concern about intake of
carbohydrates involves how fast the given
dietary carbs are broken down to glucose
within the human body
Glycemic effect refers to:
•
•
•
how quickly carbs are digested
how high blood glucose rise
how quickly blood glucose levels return to
normal
Glycemic index (GI) has been developed for
rating foods
Chemistry 121, Winter 2011, LA Tech
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