Download Reduction of Monosaccharides

Reduction of Monosaccharides
Monosaccharides can be
reduced
• turning the carbonyl group into an alcohol
group.
• producing sugar alcohols called alditols.
• and the products named by replacing the ose ending with
-itol.
D-Glucose reduces to D-Glucitol, also
called D-Sorbitol.
eduction of Monosaccharides
H
O
CH2OH
C
H
HO
H
OH
H
+ H2
Pt
HO
OH
H
H
OH
H
OH
H
OH
H
OH
CH2OH
D-glucose
CH2OH
D-glucitol or D-sorbitol
Other
artificial
sweeteners:
xylitol
mannitol
Oxidation of D-Glucose, a Reducing
Sugar
Glucose is oxidized to a
carboxylic acid.
Benedict’s
reagent
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Chapter 15, Section 2
3
Oxidation of Fructose
Fructose, a ketohexose, is also a reducing sugar. In a basic
solution such as Benedict's, the carbonyl group moves
from carbon 2 to carbon 1, so it can be oxidized as
glucose.
© 2013 Pearson Education, Inc.
Chapter 15, Section 2
4
Learning Check
Write the products of the oxidation and reduction of
D-Mannose.
O
C H
HO
H
HO
H
H
OH
H
OH
CH2OH
D-Mannose
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Chapter 15, Section 2
5
Solution
Write the products of the oxidation and reduction of
D-Mannose.
CH2OH
HO
H
HO
H
Reduction
O
O
C H
C OH
HO
H
HO
H
Oxidation
HO
H
HO
H
H
OH
H
OH
H
OH
H
OH
H
OH
H
OH
CH2OH
D-Mannitol
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CH2OH
D-Mannose
Chapter 15, Section 2
CH2OH
D-Mannonic acid
6
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.
Cyclic Acetals
Cyclic acetals
• form when an alcohol adds to a cyclic hemiacetal.
• are very important in carbohydrate chemistry.
It is the type of linkage that bonds glucose molecules to other glucose
molecules in the formation of disaccharides and polysaccharides.
Maltose
Maltose is
• a disaccharide also known as malt sugar.
• used in cereals, candies, and brewing.
• When maltose in the starches in barley is hydrolyzed
by yeast with an enzyme, maltase, two molecules of
glucose are obtained.
• The glucose can undergo fermentation and we have
beer.
Maltose + H2O
(in barley)
maltase
glucose + glucose
fermentation
ethanol
(beer)
Formation of Maltose
Lactose
Lactose
• Makes up 6-8% of human milk and 4-5% of cow’s milk.
• People who are lactose intolerant, do not produce enough
of the enzyme lactase, which is used to break down
lactose.
• The lactose reaches the colon and is broken down there by
bacteria. (this causes discomfort)
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Chapter 15, Section 1
11
Lactose
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Chapter 15, Section 1
12
Sucrose
Sucrose, or table sugar,
 is obtained from sugar cane and sugar beets.
 is hydrolyzed in the body by the enzyme sucrase to form
glucose and fructose.
 It is estimated that each person in the U.S. consumes an
average of 150 lbs. of sucrose every year.
Sucrose + H2O
sucrase
glucose + fructose
Sucrose
Learning Check
Draw the Haworth structures and give the
names of the
two monosaccharides that form when sucrose
is
hydrolyzed.
Solution
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Chapter 15, Section 2
16
Polysaccharides
Polysaccharides
• are polymers of many monosaccharides linked together.
• differ in the type of links between monosaccharides, and
the monosaccharides in the polymer.
• differ by the amount of branching in the polymer.
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Chapter 15, Section 1
17
Important Polysaccharides
Important polysaccharides include
• starches made of -D-glucose molecules, amylose, and
amylopectin.
• glycogen (animal starch in muscle), which is made of -Dglucose.
• cellulose (plants and wood), which is made of -D-glucose.
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Chapter 15, Section 1
18
Structures of Amylose and
Amylopectin
amylose
amylopectin
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.
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Chapter 15, Section 2
20
Cellulose
Cellulose
• is a major structural unit of wood and plants.
• Cotton is almost pure cellulose.
• Structure is similar to amylose where the glucose forms a
long unbranched chain.
• The difference is that amylose makes α-1,4-glycosidic bonds
and cellulose makes β-1,4- glycosidic bonds.
• Therefore, cellulose does not coil into a helical shape.
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Chapter 15, Section 1
21
Cellulose
The polysaccharide cellulose is composed of glucose units
connected by β-1,4-glycosidic bonds.
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Chapter 15, Section 1
22
Learning Check
Identify the polysaccharides and types of glycosidic
bonds in each of the following.
A.
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B.
Chapter 15, Section 1
23
Solution
Identify the polysaccharides and types of glycosidic
bonds in each of the following.
-1,4-glycosidic bonds
A.
Cellulose
B.
Amylose -1,4-glycosidic bonds
Amylopectin -1,4- and
-1,6-glycosidic bonds