CHAPTER 20: Carbohydrates
General, Organic, & Biological Chemistry
Janice Gorzynski Smith
CHAPTER 20: Carbohydrates
Learning Objectives:
 Identify carbohydrates
 Describe properties and types (monosaccharides to polysaccharides)
 Draw Fischer projections of carbohydrates
 Classify as D or L
 ID multiple chiral center and draw enantiomers
 Draw common monosaccharides: glucose, galactose, fructose
 Draw cyclic monosaccharides & identify hemiacetal
  &  isomers
 draw Haworth projections
 Draw ketohexose
 Reduction & oxidation of monosaccharides
 Describe & draw disaccharides
 Polysaccharides: types and structures
 Describe blood types
CH 20 Homework:
End of Chapter problems: 30, 34, 36, 38, 40, 42, 46, 52, 56, 58, 62, 66, 68,
74, 76, 82, 84
Smith, Janice Gorzynski. General, Organic,
& Biological Chemistry 2nd Ed.
2
Carbohydrates
Definition
•Carbohydrates, called sugars and starches, are
polyhydroxy aldehydes or ketones, or compounds
that can be hydrolyzed to them.
•The simplest carbohydrates are monosaccharides.
Smith, Janice Gorzynski. General, Organic,
& Biological Chemistry 2nd Ed.
3
Carbohydrates
Monosaccharides
generally have 3 to 6 C atoms in a
chain with an aldehyde or ketone
ending and many –OH groups.
Smith, Janice Gorzynski. General, Organic,
& Biological Chemistry 2nd Ed.
Aldehyde
monosaccharides are
aldoses
ketone
monosaccharides are
ketoses.
4
Disaccharides
Carbohydrates
Disaccharides are
composed of two monosaccharide units joined
together by forming an
acetal.
Smith, Janice Gorzynski. General, Organic,
& Biological Chemistry 2nd Ed.
5
Carbohydrates
Definition
Polysaccharides are composed of three or more
monosaccharide units joined together.
Smith, Janice Gorzynski. General, Organic,
& Biological Chemistry 2nd Ed.
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Carbohydrates
Monosaccharides
•The simplest aldose is glyceraldehyde.
•The simplest ketose is dihydroxyacetone.
A monosaccharide is characterized by the number
of C atoms in its chain:
•A triose has 3 C’s.
•A tetrose has 4 C’s.
•A pentose has 5 C’s.
•A hexose has 6 C’s.
The terms are then combined with the words aldose
and ketose:
•Glyceraldehyde is an aldotriose.
•Dihydroxyacetone is a ketotriose.
Smith, Janice Gorzynski. General, Organic,
& Biological Chemistry 2nd Ed.
7
Carbohydrates
Monosaccharides
•Monosaccharides are sweet tasting, but their
relative sweetness varies greatly.
•They are polar compounds with high melting
points.
•The presence of so many polar functional groups
capable of hydrogen bonding makes the
monosaccharides very water soluble.
Smith, Janice Gorzynski. General, Organic,
& Biological Chemistry 2nd Ed.
8
Carbohydrates
Monosaccharides: Chirality
•The prefix D is used when the –OH group is drawn
on the right side of the carbon chain.
•The prefix L is used when the –OH group is drawn
on the left side of the carbon chain.
•The wedged and dashed lines can be re-drawn in
a Fischer projection formula:
Smith, Janice Gorzynski. General, Organic,
& Biological Chemistry 2nd Ed.
9
Carbohydrates
Monosaccharides: Chirality
Glucose has four chirality centers and is drawn as:
Smith, Janice Gorzynski. General, Organic,
& Biological Chemistry 2nd Ed.
10
Carbohydrates
D vs L Monosaccharides
The configuration of the chirality center farthest
from the carbonyl group determines whether
a monosaccharide is D or L.
All naturally occurring sugars are D sugars.
Smith, Janice Gorzynski. General, Organic,
& Biological Chemistry 2nd Ed.
11
Carbohydrates
Common Monosaccharides
•Glucose (dextrose) is blood sugar and the most abundant monosaccharide.
•Normal blood glucose levels are 70-110 mg/dL.
•Excess glucose is stored as the polysaccharide glycogen or as fat.
•Fructose is one of the components of the disaccharide sucrose.
•Galactose is one of the components of the disaccharide lactose.
•Patients with galactosemia lack an enzyme needed to metabolize
galactose, which accumulates and causes cataracts and cirrhosis.
Smith, Janice Gorzynski. General, Organic,
& Biological Chemistry 2nd Ed.
12
Carbohydrates
Cyclic Monosaccharides
When the aldehyde and alcohol are on the same
molecule, a stable cyclic hemiacetal is formed:
Smith, Janice Gorzynski. General, Organic,
& Biological Chemistry 2nd Ed.
13
Carbohydrates
Cyclic Monosaccharides
The C atom that is part of the hemiacetal is a new
chirality center, called the anomer carbon.
Haworth projections
Smith, Janice Gorzynski. General, Organic,
& Biological Chemistry 2nd Ed.
14
Carbohydrates
Mutarotation
The cyclization reaction exists in an equilibrium
called mutarotation.
Smith, Janice Gorzynski. General, Organic,
& Biological Chemistry 2nd Ed.
15
Carbohydrates
Haworth Projections
HOW TO Draw a Haworth Projection from an Acyclic
Aldohexose
Example
Draw both anomers of D-mannose in a
Haworth projection.
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Carbohydrates
Haworth Projections
HOW TO Draw a Haworth Projection from an Acyclic
Aldohexose
Step [1]
Place the O atom in the upper right corner of
a hexagon, and add the CH2OH group to the
right of the O atom.
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Carbohydrates
Haworth Projections
HOW TO Draw a Haworth Projection from an Acyclic
Aldohexose
Step [2]
Place the anomeric C on the first C clockwise from the O atom.
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Carbohydrates
Haworth Projections
HOW TO Draw a Haworth Projection from an Acyclic
Aldohexose
Step [3]
Add the other substituents to the remaining
carbons, clockwise around the ring.
19
Carbohydrates
Cyclic Fructose
Smith, Janice Gorzynski. General, Organic,
& Biological Chemistry 2nd Ed.
20
Carbohydrates
Reduction of Monosaccharides
The carbonyl group of an aldose is reduced to
a 1o alcohol using H2 with Pd.
Smith, Janice Gorzynski. General, Organic,
& Biological Chemistry 2nd Ed.
21
Carbohydrates
Oxidation of Aldoses
•The aldehyde group is easily oxidized to a
carboxylic acid using Benedict’s reagent.
•Aldoses can be oxized, while ketones cannot.
Smith, Janice Gorzynski. General, Organic,
& Biological Chemistry 2nd Ed.
22
Carbohydrates
Disaccharides
When acetal formation occurs between two monosaccharides, the bond that joins them together
is called a glycosidic linkage.
Smith, Janice Gorzynski. General, Organic,
& Biological Chemistry 2nd Ed.
23
Carbohydrates
Disaccharides
Smith, Janice Gorzynski. General, Organic,
& Biological Chemistry 2nd Ed.
24
Carbohydrates
Hydrolysis of Disaccharides
•Hydrolysis cleaves the C—O glycosidic linkage
and forms two monosaccharides.
•Hydrolysis of maltose yields 2 glucose molecules.
Smith, Janice Gorzynski. General, Organic,
& Biological Chemistry 2nd Ed.
25
Disaccharide Sweeteners
Carbohydrates
Sucrose (table sugar) is a
disaccharide consisting of 1
glucose ring and 1 fructose ring
Artificial Sweeteners:
Smith, Janice Gorzynski. General, Organic,
& Biological Chemistry 2nd Ed.
26
Carbohydrates
Polysaccharides
Cellulose makes up the insoluble fiber in our
diets, which is important in adding bulk to waste
to help eliminate it more easily.
Smith, Janice Gorzynski. General, Organic,
& Biological Chemistry 2nd Ed.
27
Carbohydrates
Polysaccharides
•Starch is a polymer made up of repeating glucose
units joined by alpha glycosodic linkages.
•Starch is present in corn, rice, wheat, and potatoes.
•The first main type of starch is amylose:
Smith, Janice Gorzynski. General, Organic,
& Biological Chemistry 2nd Ed.
28
Carbohydrates
Polysaccharides
•The second type of starch is amylopectin.
•Amylose is an unbranched polymer linked by 14--glycosidic linkages.
•Amylopectin is a branched polymer linked by 14- and 16-glycosidic linkages.
•Both starch molecules can be digested by humans using the enzyme
amylase.
Smith, Janice Gorzynski. General, Organic,
& Biological Chemistry 2nd Ed.
29
Carbohydrates
Polysaccharides
•Glycogen is the major form of polysaccharide
storage in animals, similar in structure to
amylopectin.
•It is stored mainly in the liver and in muscle cells.
•When glucose is needed for energy, glucose
units are hydrolyzed from the ends of the glycogen
polymer.
•Because glycogen is highly branched, there
are many ends available for hydrolysis.
Smith, Janice Gorzynski. General, Organic,
& Biological Chemistry 2nd Ed.
30
Carbohydrates
Polysaccharides
Smith, Janice Gorzynski. General, Organic,
& Biological Chemistry 2nd Ed.
31
Carbohydrates
Blood Type
•There are four blood types—A, B, AB, and O.
•Blood type is based on 3 or 4 monosaccharides
attached to a membrane protein of red blood cells.
•Each blood type has the monosaccharides below:
Smith, Janice Gorzynski. General, Organic,
& Biological Chemistry 2nd Ed.
32
Carbohydrates
Blood Types
•Type A blood contains a fourth monosaccharide:
•Type B contains an additional D-galactose unit.
•Type AB has both type A and type B carbohydrates.
Smith, Janice Gorzynski. General, Organic,
& Biological Chemistry 2nd Ed.
33
Carbohydrates
Blood Types
Smith, Janice Gorzynski. General, Organic,
& Biological Chemistry 2nd Ed.
34
Carbohydrates
Blood Types
Smith, Janice Gorzynski. General, Organic,
& Biological Chemistry 2nd Ed.
35
Carbohydrates
Blood Types
•The blood of one individual may contain antibodies
to another type.
•Those with type O blood are called universal
donors, because people with any other blood type
have no antibodies to type O.
•Those with type AB blood are universal recipients
because their blood contains no antibodies to
A, B, or O.
Smith, Janice Gorzynski. General, Organic,
& Biological Chemistry 2nd Ed.
36