1. Chapter 13 Carbohydrates
13.1
Carbohydrates

2. Carbohydrates Carbohydrates are a major source of energy from our diet
made from elements carbon, hydrogen, and oxygen
also called saccharides, which means “sugars”

3. 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

4. Types of Carbohydrates
The types of carbohydrates are
monosaccharides, the simplest carbohydrates
disaccharides, which consist of two monosaccharides
polysaccharides, which contain many monosaccharides

5. Monosaccharides Monosaccharides
consist of three to eight carbon chains with one carbon in a carbonyl group
are further classified as an aldose, which contains an aldehyde group, or a ketose, which contains a ketone carbonyl group
have several hydroxyl groups

6. Types of Monosaccharides
Monosaccharides are also classified by the number of carbon atoms present. triose (3 C atoms) tetrose (4 C atoms) pentose (5 C atoms) hexose (6 C atoms) An aldopentose indicates a five-carbon saccharide with an aldehyde group.

7. Aldoses O Aldoses are monosaccharides with ║ an aldehyde group
C─H aldose
HCOH
CH2OH
Erythose, an aldotetrose
Aldoses are monosaccharides with
an aldehyde group
many hydroxyl (OH) groups

8. Ketoses Ketoses are monosaccharides with CH2OH a ketone group
many hydroxyl (OH) groups
CH2OH
C=O ketose
HCOH
Fructose, a ketohexose

9. Learning Check
Identify each as aldo- or keto- and as tetrose, pentose, or hexose.
A B.

10. Solution
Identify each as aldo- or keto- and as tetrose, pentose, or hexose.
A. aldohexose B. ketopentose

11. Fischer Projections of Monosaccharides
Chapter 13 Carbohydrates
13.2
Fischer Projections of Monosaccharides

12. Fischer Projections A Fischer projection
is used to represent carbohydrates
places the most oxidized group at the top
shows chiral carbons as the intersection of vertical and horizontal lines

13. D and L Notations In a Fischer projection, the OH group on the
chiral carbon farthest from the carbonyl group determines an L or D isomer.
left is assigned the letter L for the L form
right is assigned the letter D for the D form

14. Examples of D and L Isomers of Monosaccharides

15. Learning Check Identify each as the D or L isomer. A. B. C.
__-Ribose __-Threose __-Fructose

16. Solution Identify each as the D or L isomer. A. B. C.
L-Ribose L-Threose D-Fructose

17. Glucose and Fructose D-glucose is
found in fruits, corn syrup, and honey
an aldohexose with the formula C6H12O6
known as dextrose and blood sugar in the body
D-fructose is
obtained from lactose
important in cell membranes of the brain and nerve cells

18. Glucose and Fructose
The sweet taste of honey comes from the monosaccharides D-glucose and D-fructose.

19. Blood Glucose Level In the body,
glucose has a normal blood level of 70–90 mg/dL
a glucose tolerance test measures blood glucose for several hours after ingesting glucose

20. D-Galactose D-Galactose is an aldohexose, C6H12O6
is not found free in nature
is obtained from lactose, a disaccharide
has a similar structure to glucose except for the OH on carbon 4
In a condition called galactosemia, an
enzyme needed to convert galactose to
glucose is missing.

21. Learning Check
Draw the structure of D-fructose.

22. Solution

23. Haworth Structures of Monosaccharides
Chapter 13 Carbohydrates
13.3
Haworth Structures of Monosaccharides

24. Cyclic Structures Cyclic structures
are the prevalent form of monosaccharides with five or six carbon atoms
form when the hydroxyl group on carbon 5 reacts with the aldehyde group or ketone group

25. Guide for Drawing Hayworth Structures

26. Drawing the Cyclic Structure for Glucose
Step 1 Number the carbon chain and turn clockwise to form a
linear open chain.

27. Drawing the Cyclic Structure for Glucose
Step 2 Fold clockwise to make a hexagon.
Bond the carbon 5 –O– to carbon 1.
Place the carbon 6 group above the ring.
Write the –OH groups on carbon 2 and 4 below the ring.
Write the –OH group on carbon 3 above the ring.
Write a new –OH on carbon 1.

28. Drawing the Cyclic Structure for Glucose

29. Drawing the Cyclic Structure for Glucose
Step 3 Write the new –OH on carbon 1 down for the  form
and up for the  form.

30. Mutarotation of -D-Glucose and β-D-Glucose in Solution
When placed in solution,
cyclic structures open and close
-D-glucose converts to β-D-glucose and vice versa
at any time, only a small amount of open chain forms
-D-Glucose D-Glucose (open) β-D-Glucose
(36%) (trace) (64%) O H C 2 O H C 2 O H C 2

31. Cyclic Structure of Fructose
is a ketohexose
forms a cyclic structure
reacts the —OH on carbon 5 with the C=O on carbon 2 O C H 2
D-Fructose
α-D-Fructose
-D-Fructose

32. Learning Check
Write the cyclic forms of D-galactose.

33. Solution
Step 1 Number the carbon chain and turn clockwise to form a linear open chain. 1 2 3 4 5 6

34. Solution Step 2 Fold clockwise to make a hexagon.
Bond the carbon 5 O to carbon 1 and change the =O to OH on carbon 1.
Place the carbon 6 group above the ring.
Write the OH groups on carbon 2 and
carbon 4 below the ring and
the OH group on
carbon 3 above the ring.

35. Solution   Step 3 Write the new –OH on carbon 1 down for the  form
or up for the  form.  
-D-Galactose -D-Galactose

36. Chemical Properties of
Chapter 13 Carbohydrates
13.4
Chemical Properties of
Monosaccharides

37. Reducing Sugars Reducing sugars
are monosaccharides that can be oxidized to give a carboxylic acid
contain an aldehyde group in the open chain form
undergo reaction in the Benedict’s test
include the monosaccharides glucose, galactose, and fructose

38. Oxidation of D-Glucose

39. Conversion of Fructose to Glucose
Fructose, a ketohexose, is also a reducing sugar.
In Benedict’s solution, which is basic, a rearrangement occurs between the ketone group on carbon 2 and the hydroxyl group on carbon 1.
This produces an aldehyde group with an adjacent hydroxyl, thereby converting fructose to glucose.

40. Reduction of Monosaccharides
The reduction of monosaccharides
produces sugar alcohols, or alditols
involves the reduction of the carbonyl group to an alcohol
such as D-glucose gives D-glucitol, also called sorbitol

41. Learning Check
Write the products of the oxidation and reduction of D-mannose.
D-Mannose

42. Solution Write the products of the oxidation and reduction of
D-mannose.
D-Mannitol D-Mannose D-Mannonic acid

43. Chapter 13 Carbohydrates
13.5
Disaccharides

44. Important Disaccharides
A disaccharide consists of two monosaccharides.
Monosaccharides Disaccharide
glucose + glucose maltose + H2O
glucose + galactose lactose + H2O glucose + fructose sucrose + H2O

45. Maltose Maltose is a disaccharide also known as malt sugar
composed of two D-glucose molecules
obtained from the hydrolysis of starch
used in cereals, candies, and brewing
found in both the  and β forms

46. Formation of Maltose
Maltose is linked by an -1,4-glycosidic bond formed from the  OH on carbon 1 of the first glucose and OH on carbon 4 of the second glucose.

47. Lactose Lactose is found in milk and milk products
is a disaccharide of β-D-galactose and α- or β-D-glucose
contains a β-1,4-glycosidic bond

48. Sucrose Sucrose, or table sugar,
is obtained from sugar cane and sugar beets
consists of α-D-glucose and β-D-fructose
has an α,β-1,2-glycosidic bond

49. Sucrose

50. Learning Check
For the following disaccharide, list the two monosaccharide units and the type of glycosidic bond present.

51. Solution
For the following disaccharide, provide the reaction for two monosaccharide units and the type of glycosidic bond present. galactose + glucose melibiose + H2O The sugar melibiose is formed from two monosaccharides, galactose and glucose, which are joined by a -1,6-glycosidic bond.

52. Sweetness of Sweeteners
Sugars and artificial
sweeteners
differ in sweetness
are compared to sucrose (table sugar), which is assigned a value of 100

53. Artificial Sweeteners - Sucralose
Sucrolose is made from sucrose by replacing some of the hydroxyl groups with chlorine atoms.

54. Artificial Sweeteners - Aspartame
Aspartame is
marketed as Nutra-Sweet
a noncarbohydrate sweetener made from aspartic acid and a methyl ester of the amino acid phenylalanine

55. Learning Check
Identify the monosaccharides in each of the following: A. Lactose (1) α-D-Glucose (2) β-D-Fructose (3) β-D-Galactose B. Maltose (1) α-D-Glucose (2) β-D-Fructose (3) β-D-Galactose C. Sucrose (1) α-D-Glucose (2) β-D-Fructose (3) β-D-Galactose

56. Solution
Identify the monosaccharides in each of the following: A. Lactose (1) α-D-Glucose (3) β-D-Galactose B. Maltose (1) α-D-Glucose C. Sucrose (1) α-D-Glucose (2) β-D-Fructose

57. Chapter 13 Carbohydrates
13.6
Polysaccharides

58. Polysaccharides Polysaccharides are polymers of D-glucose
include amylose and amylopectin, starches made of α-D-glucose
include glycogen (animal starch in muscle), which is made of α-D-glucose
include cellulose (plants and wood), which is made of β-D-glucose
α-D-Glucose

59. Polysaccharide: Amylose
Amylose is
a straight-chain polysaccharide made of glucose molecules
linked by -1,4 glycosidic bonds

60. Polysaccharide: Amylopectin
Amylopectin, found in plants,
is a polymer of α-D-glucose molecules
is a branched-chain polysaccharide
has α-1,4-glycosidic bonds between the glucose units
has α-1,6 bonds to branches

61. Glycogen Glycogen, or animal starch,
is the polysaccharide that stores α-D-glucose in muscle
is similar to amylopectin, but is more highly branched
the glucose units are joined by α-1,4-glycosidic bonds, and branches occurring about every 10–15 glucose units are attached by α-1,6-glycosidic bonds

62. Cellulose Cellulose, the major structural unit of wood,
is a polysaccharide of glucose units in unbranched chains
has β-1,4-glycosidic bonds
cannot be digested by humans because humans cannot break down β-1,4-glycosidic bonds

63. Learning Check Identify the polysaccharides and types of glycosidic
bonds in each of the following:
A. B.

64. Solution
Identify the polysaccharides and types of glycosidic bonds in each of the following: A. Cellulose -1,4-glycosidic bonds B. Amylose -1,4-glycosidic bonds Amylopectin -1,4- and -1,6-glycosidic bonds

65. Concept Map for Carbohydrates