1. General, Organic, and Biological Chemistry
Fourth Edition
Karen Timberlake
Chapter 15
Carbohydrates
15.1 Carbohydrates
Lectures
© 2013 Pearson Education, Inc.

2. Carbohydrates Glucose is a carbohydrate
produced by photosynthesis in plants from CO2, H2O, and energy from the sun.
oxidized in living cells (respiration) to produce CO2, H2O, and energy.

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

4. Carbohydrates Carbohydrates
include table sugar, lactose, and cellulose.
are made of carbon, hydrogen, and oxygen.
make up about 65% of our diet.

5. Monosaccharides Monosaccharides consist of
3 to 6 carbon atoms (typically).
a carbonyl group (aldehyde or ketone).
several hydroxyl groups.
There are two types of monosaccharide structures.
Aldoses, in which the carbonyl group on the first carbon is an aldehyde.
Ketoses, which contain a ketone carbonyl group on the second carbon.

6. Monosaccharides

7. Aldoses Aldoses are monosaccharides with an aldehyde group.
with many hydroxyl (–OH) groups.
Examples:
aldotriose (3 C atoms)
aldotetrose (4 C atoms)
aldopentose (5 C atoms)
aldohexose (6 C atoms)

8. Ketoses Ketoses are monosaccharides with a ketone group.
with many hydroxyl (–OH) groups.
Examples:
ketotriose (3 C atoms)
ketotetrose (4 C atoms)
ketopentose (5 C atoms)
ketohexose (6 C atoms)

9. Examples of Monosaccharides

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

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

12. Fischer Projections A Fischer projection
is used to represent carbohydrates.
places the most oxidized group at the top.
shows chiral carbons at 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 if it is an L or D isomer.
left is assigned the letter L for the L-isomer.
right is assigned the letter D for the D-isomer.

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

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

16. Important Monosaccharides
The hexoses glucose, galactose, and fructose are the most important monosaccharides.
The D stereoisomers are commonly found in nature and used in the cells of the body.

17. D-Glucose, C6H12O6 blood sugar is
D-Glucose, also known as dextrose or
blood sugar is
an aldohexose found in fruits, corn syrup, and honey.
found in polymers of starch, cellulose, and glycogen.
Excess glucose is converted to fat and stored.

18. D-Galactose is an aldohexose with the formula C6H12O6.
is obtained from lactose, a disaccharide.
has a similar structure to glucose except for the –OH on C4.
is important in cell membranes of the brain and nervous system.

19. D-Fructose is a ketohexose with the formula C6H12O6.
is the sweetest carbohydrate.
is found in fruit juices and honey.
is converted to glucose in the body.

20. Learning Check
Draw the Fischer projection of D-fructose.

21. Solution
Draw the Fischer projection of D-fructose.

22. Haworth Structures Haworth structures are cyclic hemiacetals.
form when the C═O group and the –OH are part of the same molecule.
of hexoses form when the –OH on C5 reacts with a C═O group.
of a D-isomer place the –CH2OH of C6 above the ring.

23. Guide to Drawing Haworth Structures

24. Drawing the Haworth Structures for Glucose
Step 1 Turn the Fischer projection for D-Glucose clockwise by 90.

25. Drawing the Haworth Structures for Glucose
Step 2 Fold the horizontal carbon chain into a hexagon and bond the O on carbon 5 to the carbonyl group to form the hemiacetal.

26. Drawing the Haworth Structures for Glucose
Step 3 Complete the Haworth structure by drawing the –OH group on carbon 1 below the ring to give the α anomer, or above the ring to give the β anomer.

27. Mutarotation of -D-Glucose and β-D-Glucose
The process of rings opening and closing is called mutarotation. Both anomers are converted to the open chain and back to a cyclic hemiacetal.

28. Haworth Structures of Fructose
is a ketohexose.
forms Haworth structures when the –OH on C5 bonds to the C═O on C2.

29. Learning Check
Draw the Haworth structure of -D-galactose.

30. Solution
Step 1 Turn the open-chain Fischer projection clockwise by 90.

31. Solution
Step 2 Fold the horizontal carbon chain into a hexagon and bond the O on carbon 5 to the carbonyl group to form the hemiacetal.

32. Solution
Step 3 Complete the Haworth structure by drawing the –OH group on carbon 1 below the ring to give the α anomer, or above the ring to give the β anomer.

33. Urine Test for Diabetes
A symptom of diabetes mellitus is a high level of glucose in the urine.
If the blood level exceeds about 160 mg of glucose/dL of blood, the kidneys cannot reabsorb it all, and glucose spills over into the urine.
The color of a test strip
determines the glucose
level in urine.

34. Important Disaccharides
A disaccharide consists of two monosaccharides linked together.
When two monosaccharides combine in a dehydration reaction, the product is an acetal and water.

35. Maltose Maltose is a disaccharide also known as malt sugar.
composed of two D-glucose molecules.
obtained from the hydrolysis of starch.
linked by an -1,4-glycosidic bond between the
 –OH on C1 of the first glucose and –OH on C4 of the second glucose.
used in cereals, candies, and brewing.
found in both the - and - forms.

36. Formation of Maltose

37. Lactose
Lactose
is a disaccharide of -D-galactose and - or -D-glucose.
contains a -1,4-glycosidic bond.
is found in milk and milk products.
is found in both the - and -forms.

38. Lactose

39. Sucrose Sucrose, or table sugar,
is obtained from sugar cane and sugar beets.
consists of -D-glucose and -D-fructose.
has an ,-1,2-glycosidic bond.
is hydrolyzed in the body by the enzyme sucrase to form glucose and fructose.

40. Sucrose

41. Sucralose
Sucralose is made from sucrose by replacing some of the hydroxyl groups with chlorine atoms.

42. Learning Check Identify the monosaccharides in each of the following.
1. lactose
A. -D-glucose B. -D-fructose C. -D-galactose
2. maltose
A. -D-glucose B. -D-fructose C. -D-galactose
3. sucrose
A. -D-glucose B. -D-fructose C. -D-galactose

43. Solution Identify the monosaccharides in each of the following.
1. lactose
A. -D-glucose C. -D-galactose
2. maltose
A. -D-glucose
3. sucrose
A. -D-glucose B. -D-fructose

44. Important Polysaccharides
Important polysaccharides include
starches made of -D-glucose molecules, amylose, and amylopectin.
glycogen (animal starch in muscle), which is made of -D-glucose.
cellulose (plants and wood), which is made of -D-glucose.

45. Structures of Amylose and Amylopectin

46. Amylose Amylose is a polymer of -D-glucose molecules.
linked by -1,4 glycosidic bonds.
a continuous (unbranched) chain.

47. Amylopectin Amylopectin
is a branched chain polymer of -D-glucose molecules.
has -1,4-glycosidic bonds between the glucose units.
has -1,6 bonds to branches.

48. Glycogen Animal starch or glycogen is
stored in the liver and muscles of animals.
hydrolyzed in our cells to maintain glucose and energy levels between meals.
similar to amylopectin, but is more highly branched.

49. Cellulose Cellulose is a major structural unit of wood and plants.
is a polysaccharide composed of unbranched glucose units in unbranched chains.
has -1,4-glycosidic bonds.
cannot be digested by humans because humans lack the enzyme to break -1,4-glycosidic bonds.

50. Cellulose
The polysaccharide cellulose is composed of glucose units connected by β-1,4-glycosidic bonds.