Download Carbohydrates

Carbohydrates
Carbohydrates
• include table sugar,
lactose, and cellulose.
• are made of carbon,
hydrogen, and oxygen.
• make up about 65% of
our diet.
Carbon Cycle
• During photosynthesis, energy from the
sun combines CO2 and H2O to form
glucose, C6H12O6, and O2.
• During respiration in the body,
carbohydrates are oxidized to CO2 and
H2O, while energy is produced.
Types of Carbohydrates
The types of carbohydrates are
– monosaccharides, the simplest carbohydrates.
– disaccharides, which consist of two monosaccharides.
– polysaccharides, which contain many monosaccharides.
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.
Monosaccharides
Naming Monosaccharides
• The names of monosaccharides end in -ose.
• They may be named according to the number
of carbons in the monosaccharide.
triose (3 C atoms)
tetrose (4 C atoms)
pentose (5 C atoms)
hexose (6 C atoms)
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)
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)
Examples of Monosaccharides
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.
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.
Learning Check
Identify each as the D or L isomer.
A.
B.
O
H
HO
H
H
HO
H
HO
© 2013 Pearson Education, Inc.
O
C H
HO
__-Ribose
CH2OH
O
C H
CH2OH
C.
HO
H
OH
H
OH
H
H
OH
CH2OH
__-Threose
Chapter 15, Section 2
CH2OH
__-Fructose
12
Solution
Identify each as the D or L isomer.
A.
B.
C.
CH2OH
O
C H
HO
H
HO
H
H
HO
H
HO
CH2OH
__-Ribose
L
© 2013 Pearson Education, Inc.
O
O
C H
HO
H
OH
H
OH
H
H
OH
CH2OH
__-Threose
L
Chapter 15, Section 2
CH2OH
__-Fructose
D
13
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.
© 2013 Pearson Education, Inc.
Chapter 15, Section 2
14
D-Glucose, C6H12O6
D-Glucose, also known as dextrose
or
blood sugar is
• an aldohexose found in fruits, corn syrup, and
Excess
glucose is converted to fat and stored.
honey.
• found in polymers of starch, cellulose, and glycogen.
Blood Glucose Level
In the human body,
• glucose has a normal blood level of 70–90
mg/dL.
• a glucose tolerance test measures blood
glucose for several hours after ingestion.
D-Galactose
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.
© 2013 Pearson Education, Inc.
Chapter 15, Section 2
17
D-Fructose
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.
© 2013 Pearson Education, Inc.
Chapter 15, Section 2
18
Acetals and Hemiacetals
Hemiacetals (half-acetals):
• contain -a hydroxyl group –OH
-an alkoxy group –OR.
• Form when an alcohol adds to an aldehyde or ketone.
• react with a second alcohol molecule to produce an acetal.
Acetals from Ketones
Ketones:
 are less reactive than aldehydes because the carbonyl carbon is more
positive in aldehydes.
 react with one alcohol molecule to form a hemiacetal, and react with a
second alcohol molecule to form an acetal.
Cyclic Hemiacetals
In glucose, a cyclic hemiacetal between the C═O group and the –OH
group on carbon 5, forms a stable, six-atom ring.
Haworth Structures
Haworth structures
• are the prevalent form of monosaccharides
with 5 or 6 carbon atoms.
• form when the hydroxyl group on carbon 5
(C5) reacts with either the aldehyde or
ketone group.
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.
© 2013 Pearson Education, Inc.
Chapter 15, Section 2
23
Guide to Drawing Haworth Structures
Drawing the Haworth Structures for
Glucose
Step 1 Turn the Fischer projection for D-Glucose clockwise
by 90.
© 2013 Pearson Education, Inc.
Chapter 15, Section 1
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.
© 2013 Pearson Education, Inc.
Chapter 15, Section 1
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.
Mutarotation of -D-Glucose and βD-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.
© 2013 Pearson Education, Inc.
Chapter 15, Section 1
28
Haworth Structures of Fructose
Fructose
• is a ketohexose.
• forms Haworth structures when the –OH on C5 bonds
to the C═O on C2.
© 2013 Pearson Education, Inc.
Chapter 15, Section 1
29
Learning Check
Draw the Haworth structure of -D-galactose.
© 2013 Pearson Education, Inc.
Chapter 15, Section 2
30
Solution
Step 1 Turn the open-chain Fischer projection clockwise by 90.
© 2013 Pearson Education, Inc.
Chapter 15, Section 2
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.
© 2013 Pearson Education, Inc.
Chapter 15, Section 2
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.