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Pre-Lab Study Questions 29
1. What are some sources of ca
ohydrates in your diet?
2. What does the D in D-glucose mean?
3. What is the bond that links monosaccharides in di- and polysaccharides?
4. Draw the Haworth structure of each of the following:
a. -D-galactose.
. -lactose
Date Name
Section Team
Instructo
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REPORT SHEET
Types of Ca
ohydrates
LAB
29
A. Monosaccharides
1. L-Glyceraldehyde D-Glyceraldehyde
2. D-Glucose D-Galactose D-Fructose
3. -D-Glucose -D-Glucose
Date Name
Section Team
Instructor
334 Laboratory Manual for General, Organic, and Biological Chemistry
4. -D-Galactose -D-Fructose
Questions and Problems
Q1 Describe how the structure of D-glucose compares to the structure of D-galactose.
B. Disaccharides
1. -maltose
2. Equation for the hydrolysis of -maltose
3. Equation for the formation of -lactose
4. Sucrose
Types of Ca
ohydrates 335
Questions and Problems
Q2 What is the type of glycosidic bond in maltose?
Q3 Why does maltose have both and forms (anomers)? Explain.
C. Polysaccharides
1. Amylose
What is the difference in the structure of amylopectin and amylose?
2. Cellulose
336 Laboratory Manual for General, Organic, and Biological Chemistry
Questions and Problems
Q4 What is the monosaccharide that results from the complete hydrolysis of amylose?
Q5 What is the difference in the structure of amylose and cellulose?
CHE XXXXXXXXXXManual 3E.pdf
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LABORATORY GOALS
tional groups of ca
ohydrates.
LAB INFORMATION
Time: 2 h
Comments: Tear out the report sheets and place them next to the matching procedures.
In the study of ca
ohydrates, it is helpful to review stereoisomers and the
formation of hemiacetals.
Related Topics: Ca
ohydrates, monosaccharides, disaccharides, polysaccharides, hemiacetals,
stereoisomers, aldohexoses, ketohexoses, chiral compounds, Fischer projections,
Haworth structures
CHEMICAL CONCEPTS
Ca
ohydrates in our diet are our major source of energy. Foods high in ca
ohydrates include potatoes,
ead, pasta, and rice. If we take in more ca
ohydrates than we need for energy, the excess is converted
to fat, which can lead to a weight gain. The ca
ohydrate family can be organized into three classes:
monosaccharides, disaccharides, and polysaccharides.
Ca
ohydrates contained in foods such as pasta and
ead provide energy for the body.
A. Monosaccharides
Monosaccharides contain C, H, and O in units of 2 n(CH O) . Most common monosaccharides have 6
ca
on atoms (hexoses) with a general formula of 6 12 6C H O . They contain many hydroxyl groups
( OH) along with a ca
onyl group. The aldoses are monosaccharides with an aldehyde group, and
ketoses contain a ketone group.
Types of Ca
ohydrates 29
324 Laboratory Manual for General, Organic, and Biological Chemistry
Monosaccharides Sources
Glucose 6 12 6C H O Fruit juices, honey, corn syrup
Galactose 6 12 6C H O Lactose hydrolysis
Fructose 6 12 6C H O Fruit juices, honey, sucrose hydrolysis
The letters D and L refer to the orientation of the hydroxyl ( OH) group on the ca
on that is one
above the bottom ca
on. In the isomers of glyceraldehyde, the position of the OH is on the right in
the D-isomer and on the left in the L-isomer.
The hexoses glucose, galactose, and fructose are the most important monosaccharides. The most common
hexose, D-glucose, 6 12 6C H O , also known as dextrose, is found naturally in fruits, vegetables, corn
syrup, and honey; it is also the form of glucose in circulating blood, known as blood sugar. D-glucose is
a building block of the disaccharides sucrose, lactose, and maltose, and polysaccharides such as
amylose, cellulose, and glycogen. Galactose, 6 12 6C H O , is an aldohexose that is obtained from the
disaccharide lactose, which is found in milk and milk products. Galactose is important in the cellular
mem
anes of the
ain and nervous system. The only difference in D-glucose and D-galactose is the
a
angement of the OH group on ca
on 4. In contrast to glucose and galactose, fructose, 6 12 6C H O ,
is a ketohexose. The structure of fructose differs from glucose at ca
ons 1 and 2 by the location of the
ca
onyl group. Fructose is the sweetest of the ca
ohydrates; it is almost twice as sweet as sucrose
(table sugar).
Haworth Structures
Most of the time glucose exists in a ring structure, which forms when the OH on ca
on 5 bonds to
ca
on 1 in the ca
onyl group. In the Haworth structure, the new hydroxyl group may be drawn below
ca
on 1 (the form or anomer) or above ca
on 1 (the form or anomer).
Types of Ca
ohydrates 325
B. Disaccharides
A disaccharide contains two monosaccharides bonded together. Some common disaccharides include
maltose, sucrose (table sugar), and lactose (milk sugar).
Disaccharides Sources Monosaccharides
Maltose Germinating grains, starch hydrolysis Glucose glucose
Lactose Milk, yogurt, ice cream Glucose galactose
Sucrose Sugar cane, sugar beets Glucose fructose
In a disaccharide, two monosaccharides form a glycosidic bond with the loss of water. For example, in
maltose, two glucose units are linked by an -1,4-glycosidic bond.
Lactose, milk sugar, is a disaccharide found in milk and milk products. The bond between the monosac-
charides in lactose is a -1,4-glycosidic bond because it is the OH group of a form of galactose that
forms a bond with the OH group on ca
on 4 of glucose. Lactose is a reducing sugar because the
ond at ca
on 1 can open to give an aldehyde that can reduce other substances.
326 Laboratory Manual for General, Organic, and Biological Chemistry
-Lactose, a disaccharide found in milk and milk products, contains -D-galactose and -D-glucose.
C. Polysaccharides
Polysaccharides are long-chain polymers that contain many thousands of monosaccharides (usually
glucose units) joined together by glycosidic bonds. Three important polysaccharides are starch,
cellulose, and glycogen. They all contain glucose units, but differ in the type of glycosidic bonds and the
amount of
anching in the polymer.
Polysaccharides Found in Monosaccharides
Starch (amylose, amylopectin) Rice, wheat, grains, cereals Glucose
Glycogen Muscle, liver Glucose
Cellulose Wood, plants, paper, cotton Glucose
Starch is an insoluble storage form of glucose found in rice, wheat, potatoes, beans, and cereals. Starch
is composed of two kinds of polysaccharides, amylose and amylopectin. Amylose, which makes up
about 20% of starch, consists of -D-glucose molecules connected by -1,4-glycosidic bonds in a
continuous chain. A typical polymer of amylose may contain from 250 to 4000 glucose units.
Amylopectin is a
anched-chain polysaccharide that makes up as much as 80% of starch. In
amylopectin, -1,4-glycosidic bonds connect most of the glucose molecules. However, at about every
25 glucose units, there are
anches of glucose molecules attached by -1,6-glycosidic bonds between
ca
on 1 of the
anch and ca
on 6 in the main chain.
Glycogen is similar to amylopectin but it is even more highly
anched, with -1,6-glycosidic bonds
about every 10 to 15 glucose units.
Types of Ca
ohydrates 327
Cellulose is the major structural material of wood and plants. Cotton is almost pure cellulose. In cellulose,
glucose molecules form a long un
anched chain similar to amylose except that -1,4-glycosidic bonds
connect the glucose molecules. The isomers are aligned in parallel rows that are held in place by
hydrogen bonds between the rows. This gives a rigid structure for cell walls in wood and fiber and
makes cellulose more resistant to hydrolysis.
328 Laboratory Manual for General, Organic, and Biological Chemistry
Types of Ca
ohydrates 329
EXPERIMENTAL PROCEDURES GOGGLES REQUIRED!
A. Monosaccharides
Materials: Organic model kits or prepared models
1. Make or observe models of L-glyceraldehyde and D-glyceraldehyde. Draw their Fischer projections.
2. Draw the Fischer projection for D-glucose, D-galactose, and D-fructose.
3. Draw the Haworth (cyclic) structures for the and forms (anomers) for D-glucose.
4. Draw the Haworth (cyclic) structures for the forms (anomers) of D-galactose and D-fructose.
B. Disaccharides
1. Using Haworth structures, draw the structure for -maltose.
2. Using Haworth structures, write an equation for the hydrolysis of -maltose by adding 2H O to
the glycosidic bond.
3. Using Haworth structures, write an equation for the formation of -lactose from -D-galactose and
-D-glucose.
4. Draw the Haworth structure of sucrose and circle the glycosidic bond.
C. Polysaccharides
1. Using Haworth structures, draw a portion of amylose consisting of four units of -D-glucose.
Indicate the glycosidic bonds.
2. Using Haworth structures, draw a portion of cellulose consisting of four units of -D-glucose.
Indicate the glycosidic bonds.