An introduction to carbohydrates and the types of carbohydrates

1. CARBOHYDRATES

2. BIOMOLECULES OF LIFE
Carbohydrates:
Life’s
Sweet Molecules

3. Carbohydrates
Carbohydrates are
• a major source of energy
from our diet.
• composed of the elements
C, H and O.
• also called saccharides,
which means “sugars.”

4. Carbohydrates
Carbohydrates
• are produced by
photosynthesis in plants.
• such as glucose are
synthesized in plants from
CO2, H2O, and energy from
the sun.
• are oxidized in living cells to
produce CO2, H2O, and
energy.

5. • 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.

6. • 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.

7. 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.

8. • Carbohydrates also can combine with lipids to
form glycolipids
OR
• With proteins to form glycoproteins.

9. Examples of isomers:
1. Glucose
2. Fructose
3. Galactose
4. Mannose
Same chemical formula C6 H12 O6

10. EPIMERS
• EPIMERS are sugars that differ in
configuration at ONLY 1 POSITION.

11. • Examples of epimers :
– D-glucose & D-galactose (epimeric at C4)
– D-glucose & D-mannose (epimeric at C2)
– D-idose & L-glucose (epimeric at C5)

14. ENANTIOMERS
Non-Superimposable COMPLETE mirror
image (differ in configuration at EVERY
CHIRAL CENTER.

15. The two members of the pair are designated as
D and L forms.
In D form the OH group on the asymmetric
carbon is on the right.
In L form the OH group is on the left side.
D-glucose and L-glucose are enantiomers:

19. Classes of Carbohydrates
• 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.

20. 20
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.

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Monosaccharides, Continued
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.

22. Monosaccharides, Continued
• 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.

23. Monosaccharides, Continued
• 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.

24. cyclization
• Less then 1%of CHO exist in an open chain
form.
• Predominantly found in ring form.
• involving reaction of C-5 OH group with the C-1
aldehyde group or C-2 of keto group.

25. • Six membered ring structures are called
Pyranoses .
• five membered ring structures are called
Furanoses .

29. Monosaccharides, Continued
• 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.

30. Monosaccharides, Continued
• 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.

31. Oxidation and Reduction Reactions, 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.

32. Oxidation and Reduction Reactions, 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.

33. 33
Oxidation and Reduction Reactions, Continued
The product of this reaction, copper(I) oxide
(Cu2O), is not soluble and forms a brick red
precipitate in solution.

34. Oxidation and Reduction Reactions, 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.

35. Oxidation and Reduction Reactions, 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.

36. 36
Oxidation and Reduction Reactions, 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.

37. 37
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.

38. 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.

39. Disaccharides, Continued
• 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.

40. Disaccharides, Continued
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.

41. Disaccharides, Continued
• 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.

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Disaccharides, Continued

43. Chapter 5 43 © 2011 Pearson Education, Inc.
Disaccharides, Continued
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.

44. Chapter 5 44 © 2011 Pearson Education, Inc.
Disaccharides, Continued
Maltose, Continued
• The glycosidic bond is α(1→4).

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Disaccharides, Continued
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.

46. Disaccharides, Continued

47. Disaccharides, Continued
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.

48. Disaccharides, Continued

49. 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.

50. Polysaccharides
• 2 types:
– HOMOpolysaccharides (all 1 type of monomer),
e.g., glycogen, starch, cellulose, chitin
– HETEROpolysaccharides (different types of
monomers), e.g., peptidoglycans,
glycosaminoglycans

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Polysaccharides, Continued
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.

52. Chapter 5 52 © 2011 Pearson Education, Inc.
Polysaccharides, Continued
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.

53. Chapter 5 53 © 2011 Pearson Education, Inc.
Polysaccharides, Continued

54. Polysaccharides, Continued
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.

55. Glycogen
Glycogen
• is the polysaccharide that
stores α-D-glucose in
muscle.
• is similar to amylopectin,
but is more highly
branched.

56. Polysaccharides, Continued
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.

57. 57
Polysaccharides, Continued

58. Chapter 5 58 © 2011 Pearson Education, Inc.
Carbohydrates and Blood
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.

59. Carbohydrates and Blood, Continued
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.

60. • Functions:
– glucose storage (glycogen in animals & bacteria,
starch in plants)
– structure (cellulose, chitin, peptidoglycans,
glycosaminoglycans
– information (cell surface oligo- and polysaccharides,
on proteins/glycoproteins and on lipids/glycolipids)
• osmotic regulation

61. • Cellulose and chitin
– Function: STRUCTURAL, rigidity important
– Cellulose:
• homopolymer, b(1-> 4) linked glucose residues
• cell walls of plants

62. – Chitin:
• homopolymer, b(1-> 4) linked N-
acetylglucosamine residues
• hard exoskeletons (shells) of arthropods
(e.g., insects, lobsters and crabs)