Chapter 12 Outline
12.1 Monosaccharides - Aldose and ketose
-Glyceraldehyde, Stereoisomers (Mirror image = enantiomer), D and L
isomers of Glyceraldehyde
- Linear forms of: Glucose, fructose, galactose, ribose
12.3 Monosaccharides in Cyclic Forms
-Cyclic form of Glucose, Fructose and Ribose
- a and b anomers of the Glucose, Fructose, and Ribose
12.4 Disaccharides and Oligosaccharides
-Maltose, Cellobiose, lactose, sucrose
12.5 Polysaccharides: amylose, amylopectin, cellulose, glycogen, chitin,
chondroitin sulfate, hyaluronic acid
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Classification of Monosaccharides
• Aldoses - those that contain an aldehyde group.
• Ketoses - those that contain a ketone group.
• Trioses have 3 carbon atoms; tetroses have
four carbon atoms; pentoses have 5 carbon
atoms, and so on.
• An aldohexose is an aldehyde sugar with 6
carbon atoms.
• (The “ose” ending indicates that the molecule
being named is a carbohydrate).
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Chiral carbon gives rise to
stereoisomers.
(chiral carbon = asymetric carbon)
Mirror image
molecules = enantiomers
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-OH on the right side for D-isomers
Stereoisomers
• Carbohydrates contain a chiral carbon atom and
have stereoisomers.
• Enantiomers are represented using a Fischer
projection.
– In Fischer projections, chiral carbon atoms sit at the
intersection of a vertical line and a horizontal line.
– The horizontal lines represent bonds pointing toward the
viewer, and the vertical lines are for bonds pointing away
from the viewer.
– For monosaccharides, Fischer projections are drawn with
the carbon atoms running vertically and the aldehyde or
ketone group at or near the top.
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D and L sugars
• When drawn in a Fischer projection, the -OH attached to
the chiral carbon atom next to the last carbon atom (just
above the last carbon atom) points to the right in a Dmonosaccharide and to the left in an Lmonosaccharide.
• In nature, most monsaccharides are D sugars, so Dglyceraldehyde is commonly found, while Lglyceraldehyde is not.
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O
C
H
HO
H
CH2OH
OH
C
H
HO
O
C H
C H
O
H
OH
H
H
H
H
OH
H
OH
H
OH
H
OH
H
OH
H
OH
H
OH
H
OH
CH2OH
O
CH2OH
CH2OH
Ribose
CH2OH
2-dexoyribose
Fructose
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Glucose – blood sugar; the main fuel molecule for
our bodies.
Fructose – sugar from fruit
Galactose – sugar found in lactose (in milk)
Ribose – a composition of RNA
2-Deoxyribose – a composition of DNA
Important Monosaccharides
• D-Glucose is also known as blood sugar. One form of energy
storage in the body involves combining glucose molecules to
produce glycogen.
• D-Galactose is combined with glucose to produce lactose, a
disaccharide that gives milk its sweetness.
• D-Fructose, or fruit sugar, is the ketose found most often in
nature. Fructose plays a key role in energy production.
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Important Monosaccharides
• Pentoses and hexoses are the most abundant
monosaccharides found in nature.
– D-ribose and D-2-deoxyribose are aldopentoses that are often
incorporated into larger biomolecules, including NADPH, NAD+,
and the nucleic acids RNA and DNA.
– The structural difference between these two monosaccharides is
that 2-deoxyribose lacks an -OH group at carbon atom #2, hence
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the “2-deoxy” part of the name.
Examples of other kinds
of monosaccharides or
sugars. You don’t need to
know any of these
structures, just so that if
you see the carboxylic
acid, amide, amine, etc..
you recognize that these
are different sugars.
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12.3 Cyclic Hemiacetal Formation
• When the carbonyl group of an aldehyde or ketone reacts
with the hydroxyl group (-OH group) of an alcohol, a
hemiacetal forms. In D-glucose the #5 –OH group reacts
with the carbonyl group of C #1.
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Cyclic form of Glucose:
O
pyranose ring
These two forms of
Glucose are said to be
anomers (a and b
anomers).
O
furanose ring
- Mutarotation is the
interconversion of
the a and b anomer.
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Anomers
• The one with the hemiacetal -OH on
carbon 1 pointing down is called the
alpha (a) anomer and that with the -OH
group pointing up is the beta (b) anomer.
HOH2C
HOH2C
O
HO
OH
O
H
OH
OH
Which glucose anomer is this?
HO
OH
OH
H
OH
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Cyclic forms of Fructose, Ribose and Deoxyribose
HOH2C
O
CH2OH
HO
HO
HOH2C
O
H
OH
aD-fructofuransoe (or just aD-fructose)
HOH2C
OH
aD-ribofuranose
(or just aD-ribose)
H
OH
OH
HO
O
HO
aD-2-deoxyribofuranose
(or just aD-2-deoxyribose)
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12.4: Disaccharides are sugars which contain
two monosaccharide residues.
• Examples:
– Maltose (2 glucoses, a(14) bond)
– Cellobiose (2 glucoses, b(14) bond)
– Lactose (galactose –glucose, b(14) bond)
– Sucrose (glucose-fructose)
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15
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These are our
Glycolipids! Can you
spot the sphingosine
and the fatty acyl
group?
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Roles of Disaccharides:
* Maltose – form the constituents or building blocks
of amylose, amylopectin and Glycogen; use for
energy.
* Cellobiose – form the constituents or building blocks
of cellulose (cellulose fiber); leading to structural role,
not energy role.
* Galactose – milk sugar.
* Sucrose – table sugar; energy role.
Polysaccharieds:
• Carbohydrates that contain many monosaccharide residues
linked together are called polysaccharides.
• In living things, some polysaccharides help provide
structure (structural rigidity) and some act as energy storage
molecules.
We will study these polysaccharies only:
Starch (consists of amylose and amylopectin), glycogen, cellulose,
chitin, chondroitin sulfate, hiyaluronic acid
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Polysaccharides
In plants:
• Starch is produced by plants as a way to store energy.
• Starch consists of two different polysaccharides, amylose and
amylopectin, each of which is composed entirely of maltose (or
glucoses) building blocks.
Amylose – single long chain of glucoses, no branching.
Amylopectin – one long main chain of glucoses attached to branchings
(every 25 – 30 glucose residues)..
In animals or human:
• Glycogen – an energy storage polysaccharide in animals and human,
not in plants. The structure of Glycogen looks like that of
amylopectin, except it is more branching (every 8 – 12 glucose
residues).
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Amylose structure
Amylopectin or
Glycogen
structure. The
branch is the one
on top.
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• Cellulose is of major importance to the structure of
plants (wood is about 50% cellulose) because it provides
support to stems and stalks and provides a tough waterinsoluble protective barrier.
• Most animals do not produce enzymes required to
hydrolyze cellulose into cellubiose and individual
glucose molecules, so cellulose is not a good animal
food source.
• Bacteria found in the digestive tracts of horses, cows,
and termites contain cellulases (enzymes) that break
down the cellulose, which is digested.
• Chitin makes up the exoskeleton of crustaceans and
insects, and is present in the cell walls of some algae and
fungi.
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This is the
structure of
cellulose. There
is no branching.
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Structure
of chitin
Cartoon pictures
of Glycogen and
Amylopectin.
Note glycogen is
more branching.
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Other polysaccharides
• Hyaluronic acid, found to be important components of the
lubricating fluid that surrounds joints in animals (or human) body, and
in the vitreous humor (clear gel) inside the eye; it is made up of
alternating residues of N-acetyl-D-glucosamine and D-glucuronate;
contains nitrogen.
• Heparin, is a natural anticoagulant substance; it inhibits blood clotting
mechanisms.
• Chondroitin 4-sulfate consists of N-acetyl-D-galactosamine-4-sulfate
residues alternating with D-glucuronate residues. These
heteropolysaccharides are present in cartilage, tendons, and other
connective tissues; contains nitrogen and sulfate.
(Note: you don’t have to memorize anything about these two
polysaccharides.)
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Hyaluronic
acid
Chondroitin
sulfate
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Heparin
CO2-
CH2OSO3-
OH
OH
O
O
OSO3-
D-glucuronate-2-sulfate
O
NHOSO3N-sulfo-D-glucosamine-6-sulfate
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