carboydrates.ppt

Chapter 5 Lecture
General, Organic, and Biological
Chemistry: An Integrated Approach
Laura Frost, Todd Deal and Karen Timberlake
by Richard Triplett
© 2011 Pearson Education, Inc.
Carbohydrates: Life’s
Sweet Molecules
Chapter 5

Chapter 5 2
Chapter Outline
5.1 Classes of Carbohydrates
5.2 Monosaccharides
5.3 Oxidation and Reduction Reactions
5.4 Ring Formation—The Truth about
Monosaccharide Structure
5.5 Disaccharides
5.6 Polysaccharides
5.7 Carbohydrates and Blood

Chapter 5 3
Introduction to Carbohydrates
• Carbohydrates are sugars and provide energy
when consumed.
• Our bodies break down carbohydrates to extract
energy. Carbon dioxide and water are released
in the process.
• Glucose is the primary carbohydrate our bodies
use to produce energy.
• Carbohydrates are classified as biomolecules.

Chapter 5 4
Introduction to Carbohydrates, Continued
• Simple carbohydrates are referred to as
simple sugars and are often sweet to the taste.
• Consumption of more sugar than is needed for
energy results in conversion of these sugars to
fat.
• Complex carbohydrates include starches and
the plant and wood fibers known as cellulose.

Chapter 5 5
Introduction to Carbohydrates, Continued
• Carbohydrates are found on the surface of cells
where they act as “road signs” allowing
molecules to distinguish one cell from another.
• ABO blood markers found on red blood cells
are made up of carbohydrates. They allow us to
distinguish our body’s blood type from a foreign
blood type.
• Carbohydrates in our body prevent blood clots.
They are also found in our genetic material.

Chapter 5 6
• Monosaccharides are the simplest
carbohydrates. They cannot be broken down to
smaller carbohydrates.
• Disaccharides consist of two monosaccharide
units joined together; they can be split into two
monosaccharides. Sucrose, table sugar, can be
broken down into glucose and fructose.
• Oligosaccharides contain anywhere from three
to nine monosaccharide units. ABO blood
groups are oligosaccharides.

Chapter 5 7
5.1 Classes of Carbohydrates, Continued
Polysaccharides are large molecules containing
10 or more monosaccharide units. Carbohydrate
units are connected in one continuous chain or
the chain can be branched.

Chapter 5 8
5.2 Monosaccharides
• Monosaccharides contain the elements carbon,
hydrogen, and oxygen, and have the general
formula Cn(H2O)n, where n is a whole number 3
or greater.
• Monosaccharides contain several functional
groups. They contain the hydroxyl group
represented as –OH. They also contain a
carbonyl group, which is an oxygen double
bonded to a carbon atom. The carbonyl group
may be an aldehyde or a ketone.

Chapter 5 9
5.2 Monosaccharides, Continued
The functional groups of glucose are shown in
the figure below.

Chapter 5 10
Functional Groups in Monosaccharides—
Alcohols, Aldehydes, and Ketones
Alcohols
• Alcohol is an organic compound containing the
–OH group.
• Ethanol is one of the simplest alcohols and is
prepared from the fermentation of simple sugars
in grains and fruits. Ethanol is present in beer
and liquors, and is used as an alternative fuel
blend, such as gasohol and E85 (85% ethanol
and 15% gasoline).

Chapter 5 11
Alcohols
• Alcohols are classified by the number of alkyl
groups attached to the carbon atom containing
the hydroxyl group. The number of alkyl groups
impacts the reactivity of the alcohol.
• Primary (1o) alcohols have one alkyl group
attached to the alcoholic carbon.
• Secondary (2o) alcohols have two alkyl groups
• Tertiary (3o) alcohols have three alkyl groups

Chapter 5 12
Alcohols
• Monosaccharides contain both primary and
secondary alcohols.

Chapter 5 13
Aldehydes
• An aldehyde is an organic compound containing
the carbonyl group.
• Benzaldehyde, a compound responsible for the
aroma of almonds and cherries, is one example.

Chapter 5 14
Aldehydes
• Members of this family always
contain a carbonyl group with
a hydrogen atom bonded to
one side and an alkyl or
aromatic bonded to the other.
An exception is formaldehyde
(a preservative), which has
two hydrogens bonded to the
carbonyl group.

Chapter 5 15
Aldehydes
• Monosaccharides can
contain an aldehyde group
on one end of the molecule
in addition to multiple
hydroxyl groups.

Chapter 5 16
Ketones
• A ketone also contains the carbonyl group, but
has an alkyl or aromatic group on both sides of
the carbonyl group.
• Acetone is the simplest ketone. It is the main
component of fingernail polish remover.

Chapter 5 17
Ketones
• A wide variety of biologically important compounds
contain a ketone group.
• Pyruvate is a ketone-containing compound formed
during the breakdown of glucose.
• Butanedione, the flavor of butter, contains two ketone
groups.

Chapter 5 18
• Monosaccharides that contain an aldehyde
group are referred to as an aldose. Those that
contain a ketone group are referred to as a
ketose.
• Monosaccharides are classified according to the
number of carbon atoms. Most common
monosaccharides have three to six carbon
atoms.
– Triose contains three carbons.
– Tetrose contains four carbons.
– Pentose contains five carbons.
– Hexose contains six carbons.

Chapter 5 19
• Carbohydrates are further classified on whether
they contain an aldehyde or ketone group.
• For example, glucose, the most abundant
monosaccharide found is nature, contains six
carbons and an aldehyde group. It is classified
as an aldohexose.
• Fructose, known as fruit sugar, contains six
carbons and a ketone group. It is classified as a
ketohexose.

Chapter 5 20
Aldohexose and ketopentose differ in the number of
carbon atoms and in the type of carbonyl group
they contain.

Chapter 5 21
Stereochemistry in Monosaccharides
Multiple chiral centers
• Recall that a chiral center is a carbon atom that
has four different atoms or groups of atoms
attached to it.
• Glucose, a ketohexose, contains four different
chiral centers, each with a tetrahedral geometry.

Chapter 5 22
• Carbons 2 through 5 of
glucose are tetrahedral and
have four different atoms or
groups of atoms attached.
Carbons 1 and 6 are not
chiral centers. Why?

Chapter 5 23
• Groups bonded to each chiral center have two
different arrangements or mirror images, which
result in stereoisomers.
• The number of stereoisomers for a molecule
increases with the number of chiral centers in
the molecule.
• The general formula for determining the number
of stereoisomers is 2n, where n is the number of
chiral centers present in the molecule.
• Glucose has 4 chiral centers, so there are 16
stereoisomers, 24 = 16.

Chapter 5 24
Representing stereoisomers—the Fischer
projection
• Fischer projection is a simple way of indicating
chiral molecules by showing their three-
dimensional structure in two dimensions, without
showing all the wedges and dashes on all the
chiral centers.
• In the Fischer projection, horizontal lines on a
chiral center represent wedges, and vertical
lines on a chiral center represent dashes.

Chapter 5 25
• Representing stereoisomers—the Fischer
projection
– In the Fischer projection, a chiral carbon is not
shown, but is implied at the intersection of
lines.
– Consider the Fischer projection of
glyceraldehyde, the simplest aldose, shown
on the next slide.

Chapter 5 26
projection

Chapter 5 27
projection
• D and L designations of sugars are based on the
Fischer projection positioning in glyceraldehyde.
• All D-sugars have the –OH on the chiral carbon
farthest from the carbonyl group on the right side
of the molecule.
• All L-sugars have the –OH on the chiral carbon
farthest from the carbonyl group on the left side
of the molecule.
• Most sugars in nature have the D designation.

Chapter 5 28
Representing stereoisomers—the
Fischer projection
• Enantiomers are written as if there is a
mirror placed between the two molecules.
• Enantiomers of D- and L-glucose are:

Chapter 5 29
Stereoisomers that are not enantiomers
• How are all stereoisomers of D-glucose related
since only one mirror image exists for any
stereoisomer?
• Stereoisomers that are not enantiomers are
called diastereomers.
• Diastereomers are stereoisomers that are not
exact mirror images.

Chapter 5 30

Chapter 5 31
Some Important Monosaccharides
• Glucose is the most abundant monosaccharide
found in nature.
• Glucose is also known as dextrose, blood sugar,
and grape sugar.
• Glucose is broken down in cells to produce
energy.

Chapter 5 32
• Diabetics have difficulty getting glucose in their
cells, which is why they must monitor their blood
glucose levels regularly.
• Glucose is one of the monosaccharides of
sucrose (table sugar) and lactose (milk sugar)
as well as the polysaccharides glycogen, starch,
and cellulose.

Chapter 5 33
• Galactose is found combined with glucose in the
disaccharide lactose, which is present in milk
and other dairy products.
• A single chiral center (carbon 4) in galactose is
arranged opposite that of glucose, which makes
it a diastereomer of glucose.
• Diastereomers that differ by one chiral center
are called epimers.

Chapter 5 34
• Mannose, a monosaccharide, is found in some
fruits and vegetables.
• Cranberries contain high amounts of mannose,
which has been shown to be effective in urinary
tract infections.
• Mannose is an epimer of glucose.

Chapter 5 35
• Fructose, a ketose, is commonly referred to as
fruit sugar or levulose.
• Fructose is combined with glucose to give
sucrose, or table sugar.
• Fructose is the sweetest monosaccharide and is
found in fruits, vegetables, and honey.
• Fructose is not an epimer of glucose, but it can
be broken down for energy in the body.

Chapter 5 36
• Pentoses are five-carbon sugars and include
ribose and 2-deoxyribose, which are parts of
nucleic acids that make up genetic material.
• Ribonucleic acid (RNA) contains ribose, and
deoxyribonucleic acid (DNA) contains
2-deoxyribose.
• The difference between these two pentoses is
the absence of an oxygen atom on carbon 2 of
deoxyribose.
• Ribose is also found in the vitamin riboflavin and
other biologically important molecules.

Chapter 5 37
Oxidation and Reduction
• Oxidation and reduction reactions are commonly
called redox reactions.
• Oxidation is a loss of electrons.
• Reduction is a gain of electrons.
• The mnemonic “OIL RIG” helps remember redox
reactions. Oxidation Is Loss, Reduction Is Gain.

Chapter 5 38
5.3 Oxidation and Reduction Reactions,
Continued
• When copper metal (shiny orange metal) is
exposed to oxygen, an ionic compound,
copper(II) oxide, is produced. This compound is
greenish in color. This reaction is shown as:
• The copper atoms in the reactant lose electrons
to form the Cu2+ ions in the product. The copper
has undergone oxidation.

Chapter 5 39
Continued
• The electrons lost by copper atoms are
transferred to the oxygen atom, which then
becomes O2-. Oxygen has undergone reduction.
• While the copper was being oxidized, oxygen
was being reduced.
• Copper then becomes the reducing agent
(causing oxygen to be reduced) and oxygen is
the oxidizing agent (causing copper to be
oxidized).

Chapter 5 40
Continued
• Organic molecules are oxidized if they gain
oxygen or lose hydrogen, and they are reduced
if they lose oxygen or gain hydrogen.
• Some biological reactions undergo oxidation and
reduction. A summary of these characteristics
are as follows:

Chapter 5 41
Continued
Monosaccharides and Redox
• An aldehyde functional group can undergo
oxidation by gaining oxygen or it can undergo
reduction by gaining hydrogen.
• During oxidation, aldehydes form carboxylic
acids, and during reduction, they form alcohols.
• In monosaccharides, oxidation produces a sugar
acid, and reduction produces a sugar alcohol.

Chapter 5 42
Continued
• Benedict’s test is a useful test to determine the
presence of an oxidation reaction that occurs
with sugars.
• Aldose sugars are oxidized by Cu2+ ion, while
the Cu2+ ion is reduced to Cu+ ion.

Chapter 5 43
Continued
The product of this reaction, copper(I) oxide
(Cu2O), is not soluble and forms a brick red
precipitate in solution.

Chapter 5 44
Continued
• Aldoses are easily oxidized. They serve as
reducing agents and are referred to as reducing
sugars.
• Fructose and other ketoses are also reducing
sugars, even though they do not contain an
aldehyde group.
• The oxidizing agents can cause a
rearrangement of the ketose to an aldose.

Chapter 5 45
Continued
This rearrangement can be shown as:

Chapter 5 46
Continued
• Benedict’s test can be used in urine dipsticks to
determine the level of glucose in urine. Excess
glucose in urine suggests high levels of glucose
in blood, which is an indicator of diabetes.
• Aldoses or ketoses can be reduced by hydrogen
under the correct conditions, producing sugar
alcohols.
• Sugar alcohols are produced commercially as
artificial sweeteners and found in sugar-free
foods.

Chapter 5 47
Continued
Reduction of glucose produces the sugar alcohol,
sorbitol, which is an artificial sweetener.

Chapter 5 48
Continued
• When glucose levels are high in the blood
stream, sorbitol can be produced by an enzyme
called aldose reductase.
• High levels of sorbitol can contribute to
cataracts, which is a clouding of the lens in the
eye.
• Cataracts are commonly seen in diabetics.

Chapter 5 49
• Carbonyl groups can also react with a hydroxyl
functional group (–OH).
• When this happens, a hemiacetal functional
group is formed as shown:

Chapter 5 50
Monosaccharide Structure, Continued
A hemiacetal can form within a monosaccharide
since it contains both a carbonyl and several
hydroxyl functional groups.

Chapter 5 51
• The carbonyl carbon that reacts to form the
hemiacetal is referred to as the anomeric
carbon.
• Two ring arrangements can be produced. These
are termed anomers, and are referred to as the
alpha () and beta (β) anomer.
• The position of the –OH group on the anomeric
carbon relative to the position of the carbon
outside the ring determines the type of anomer
present.

Chapter 5 52
• In the six-member ring (five carbons and an
oxygen) form of D-isomers, called a pyranose,
carbon 6 is always drawn on the top side of the
ring.
• In the  anomer, the –OH on the anomeric
carbon is trans to the carbon outside the ring.
• In the β anomer, the –OH on the anomeric
carbon is cis to the carbon outside the ring.

Chapter 5 53
• D-Fructose contains both a ketone group and
several hydroxyl groups.
• The ring structure of D-fructose contains four
carbons and an oxygen to form a five-membered
ring called a furanose.
• In a furanose, carbons 1 and 6 remain outside
the ring.

Chapter 5 54

Chapter 5 55
• In a five-membered and six-membered ring, the
anomers are distinguished similarly.
• In the alpha anomer, the –OH on the anomeric
carbon is trans to the carbon outside the ring.
• In the beta anomer, the –OH on the anomeric
carbon is cis to the carbon outside the ring.

Chapter 5 56
5.5 Disaccharides
Condensation and Hydrolysis—Forming and
Breaking Glycosidic Bonds
• The –OH group that is most reactive in a
monosaccharide is the one on the anomeric carbon.
• When this hydroxyl group reacts with another hydroxyl
group on another monosaccharide a glycosidic bond
is formed.

Chapter 5 57
5.5 Disaccharides, Continued
Formation of glycosides is an example of
another type of organic reaction. During this
reaction, a molecule of water is eliminated as
two molecules join.

Chapter 5 58
• Condensation reaction is a type of reaction
that occurs when two molecules are joined and
a water molecule is produced. This type of
reaction is referred to as a dehydration
reaction.
• Hydrolysis reaction is the reverse of a
condensation reaction. A larger molecule forms
two smaller molecules and water is consumed
as a reactant.

Chapter 5 59
Condensation reactions occur between different
types of functional groups that contain an –H in
a polar bond, like O–H or N–H, and an –OH
group that can be removed to form water.

Chapter 5 60
Naming Glycosidic Bonds
• In the slide showing the formation of maltose, we
observed that the glycosidic bond was in the
alpha position. If that bond had been in the beta
position, a different molecule would have been
formed with a different three-dimensional
structure.
• In naming glycosidic bonds, it is necessary to
name the configuration as well as the carbons
involved in the bond formation.

Chapter 5 61
• In the case of maltose, the glycosidic bond is
specified as α(1→4) and is simply stated as
alpha-one-four.
• If the –OH group had been in the beta
configuration when the glycosidic bond was
formed, the bond would be in the β(1→4)
configuration. The molecule formed would be
named cellobiose and would have a different
two-dimensional and three-dimensional shape
than maltose.

Chapter 5 62

Chapter 5 63
Three Important Disaccharides—Maltose,
Lactose, and Sucrose
The formation of these three common
disaccharides is outlined below.

Chapter 5 64
Maltose
• Maltose is known as malt sugar.
• It is formed by the breakdown of starch.
• Malted barley, a key ingredient in beer,
contains high levels of maltose.
• During germination of barley seeds, the starch
goes through hydrolysis to form maltose. This
process is halted by drying and roasting
barley seeds prior to their germination.
• One of the anomeric carbons is free, so
maltose is a reducing sugar.

Chapter 5 65
Maltose, Continued
• The glycosidic bond is α(1→4).

Chapter 5 66
Lactose
• Lactose is known as milk sugar.
• It is found in milk and milk products.
• An intolerance to lactose can occur in people
who inherit or lose the ability to produce the
enzyme lactase that hydrolyzes lactose into
its monosaccharide units.
• The glycosidic bond is (1→4).
• One of the anomeric carbons is free, so
lactose is a reducing sugar.

Chapter 5 67

Chapter 5 68
Sucrose
• Sucrose is known as table sugar.
• It is the most abundant disaccharide found in
nature.
• Sucrose is found in sugar cane and sugar
beets.
• The glycosidic bond is  (1→2).
• Both anomeric carbons of the
monosaccharides in sucrose are bonded,
therefore, sucrose is not a reducing sugar. It
will not react with Benedict’s reagent.

Chapter 5 69

Chapter 5 70
5.6 Polysaccharides
Polysaccharides
Polysaccharides are large molecules of
monosaccharides that are connected to each
other through their anomeric carbons. There are
two types of polysaccharides:
1. Storage polysaccharides contain only  -glucose
units. Three important ones are starch, glycogen,
and amylopectin.
2. Structural polysaccharides contain only -glucose
units. Two important ones are cellulose and chitin.
Chitin contains a modified -glucose unit.

Chapter 5 71
5.6 Polysaccharides, Continued
Storage and structural polysaccharides are made
up of glucose units, but they are structurally and
functionally different because of their glycosidic
bonds and difference in branching.

Chapter 5 72

Chapter 5 73
Storage Polysaccharides
Amylose and amylopectin—starch
• Starch is a mixture of amylose and amylopectin
and is found in plant foods.
• Amylose makes up 20% of plant starch and is
made up of 250–4000 D-glucose units bonded
α(1→4) in a continuous chain.
• Long chains of amylose tend to coil.
• Amylopectin makes up 80% of plant starch and
is made up of D-glucose units connected by
α(1→4) glycosidic bonds.

Chapter 5 74
Amylose and amylopectin—starch
• About every 25 glucose units of amylopectin, a
branch of glucose units are connected to the
glucose by an α(1→6) glycosidic bond.
• During fruit ripening, starch undergoes
hydrolysis of the α(1→4) bonds to produce
glucose and maltose, which are sweet.
• When we consume starch, our digestive system
breaks it down into glucose units for use by our
bodies.

Chapter 5 75

Chapter 5 76
Glycogen
• Glycogen is a storage polysaccharide found in
animals.
• Glycogen is stored in the liver and muscles.
• Its structure is identical to amylopectin, except
that α(1→6) branching occurs about every
12 glucose units.
• When glucose is needed, glycogen is
hydrolyzed in the liver to glucose.

Chapter 5 77
Structural Polysaccharides
Cellulose
• Cellulose contains glucose units bonded
(1→4).
• This glycosidic bond configuration changes the
three-dimensional shape of cellulose compared
with that of amylose.
• The chain of glucose units is straight. This
allows chains to align next to each other to form
a strong rigid structure.

Chapter 5 78

Chapter 5 79
Cellulose
• Cellulose is an insoluble fiber in our diet
because we lack the enzyme cellulase to
hydrolyze the (1→4) glycosidic bond.
• Whole grains are a good source of cellulose.
• Cellulose is important in our diet because it
assists with digestive movement in the small and
large intestine.
• Some animals and insects can digest cellulose
because they contain bacteria that produce
cellulase.

Chapter 5 80
Chitin
• Chitin makes up the exoskeleton of insects and
crustaceans and cell walls of some fungi.
• It is made up of N-acetylglucosamine containing
(1→4) glycosidic bonds.
• It is structurally strong.
• Chitin is used as surgical thread that
biodegrades as a wound heals.
• It serves as a protection from water in insects.
• Chitin is also used to waterproof paper, and in
cosmetics and lotions to retain moisture.

Chapter 5 81

Chapter 5 82
ABO Blood Types
• ABO blood types refer to carbohydrates on red
blood cells.
• These chemical markers are oligosaccharides that
contain either three or four sugar units.
• Sugar units are D-galactose, L-fucose,
N-acetylglucosamine, and N-acetylgalactosamine.

Chapter 5 83
5.7 Carbohydrates and Blood, Continued
The following shows the carbohydrates and their
attachments in type O, type A, and type B blood.
Type AB blood has both type A and type B sets on
their blood cells.

Chapter 5 84
• Type O blood is considered the universal donor
while type AB blood is considered the universal
acceptor.
• The following table shows the compatibility of
blood groups.

Chapter 5 85
Heparin
• Heparin is a medically important polysaccharide
because it prevents clotting in the bloodstream.
• It is a highly ionic polysaccharide of repeating
disaccharide units of an oxidized
monosaccharide and D-glucosamine. Heparin
also contains sulfate groups that are negatively
charged.
• It belongs to a group of polysaccharides called
glycosaminoglycans.

Chapter 5 86

Chapter 5 87
Chapter Summary
Carbohydrates are classified as monosaccharides
(simple sugars), disaccharides (two
monosaccharide units), oligosaccharides (three to
nine monosaccharide units), and polysaccharides
(many monosaccharide units).

Chapter 5 88
Chapter Summary, Continued
5.2 Monosaccharides
• A monosaccharide has a molecular formula of
Cn(H2O)n, where n = 3–6.
• Fischer projections that highlight chiral centers
are used to represent monosaccharides.
• Most monosaccharides in nature are D-isomers.

Chapter 5 89
• Multiple chiral centers lead to enantiomers or
diastereomers.
• Important monosaccharides are glucose,
galactose, fructose, mannose, ribose, and
deoxyribose.

Chapter 5 90
• Oxidation is a loss of electrons and reduction
is a gain of electrons.
• These are common types of reactions in organic
molecules.
• For organic molecules, oxidation is the addition
of oxygen and reduction is the addition of
hydrogen.

Chapter 5 91
Continued
• The anomeric carbon of carbohydrates is highly
reactive and can be oxidized to a carboxylic acid
or reduced to an alcohol.
• Monosaccharides are considered reducing
sugars because their anomeric carbon can react.

Chapter 5 92
• A hydroxyl group and the carbonyl group can
react to enclose the hydroxyl’s oxygen in a ring.
• Because the carbonyl group is planar, two
possible ring arrangements about the anomeric
carbon occur when the ring forms. These are
termed the α and  anomers.

Chapter 5 93
5.5 Disaccharides
• Condensation and hydrolysis are common
reactions that occur in biomolecules.
• Condensation reactions produce a water
molecule while bonding two molecules together.
• Hydrolysis reactions consume a molecule of
water while a molecule is broken into two
smaller molecules.

Chapter 5 94
• Carbohydrates form glycosides when an
anomeric carbon reacts with a hydroxyl group on
a second molecule. The bond formed is called a
glycosidic bond.
• Glycosidic bonds are named by designating the
anomer of the reacting monosaccharide and the
carbons that are bonded, for example, α(1→4).

Chapter 5 95
5.6 Polysaccharides
• A polysaccharide consists of many
monosaccharide units bonded together through
glycosidic bonds.
• Glucose is stored as glycogen in animals and
starch in plants.
• Starch consists of amylose, a linear chain of
glucose, and amylopectin, a branched chain of
glucose.

Chapter 5 96
• Glycogen contains many more branches in its
structure than amylopectin.
• Two important polysaccharides are cellulose in
plants and chitin in arthropods and fungi.
• Cellulose consists of (1→4) and is the
structural component of plants. It has a linear
structure.

Chapter 5 97
• Chitin is linear. It contains N-acetylglucosamine.
• Cellulose and chitin form strong, water-resistant
materials when the linear chains are aligned to
each other.

Chapter 5 98
• The ABO blood groups are oligosaccharides
on the surface of red blood cells.
• The O blood group is considered the universal
donor.
• Heparin, a polysaccharide, functions in the
blood as an anticoagulant and is found as a
coating on medical tubing and syringes during
blood transfusions.

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