Chapter 4
The Carbohydrates: Sugars,
Starches, and Fibers
O
N
C
Oxygen
Nitrogen
Carbon
H
Hydrogen
H H
H
N C C O H
H C C O H
H H
Ethanol
H H
H
H H
Ethanolamine
Carbohydrates
 most abundant class of compounds found
in nature
 contain the elements C, H and O
 term “CARBOHYDRATES” came from fact
that these compounds could be written as
“hydrates of carbon”
e.g.
C6H12O6
=
C6(H2O)6
Simple Carbohydrates (sugars)
Monosaccharides
CH2OH
O OH
H
H
OH H
H
HO
H
OH
Glucose
Simple Carbohydrates (sugars)
Monosaccharides
CH2OH
O OH
H
H
OH H
H
HO
H
OH
Glucose
CH2OH
O OH
HO
H
OH H
H
H
H
OH
Galactose
Simple Carbohydrates (sugars)
Monosaccharides
HOH2C
O CH2OH
H
HO
H
OH
OH
H
Fructose
Simple Carbohydrates (sugars)
Disaccharides
Maltose
CH2OH
CH2OH
O H
H
O OH
H
H
H
OH H
OH H
HO
H
O
H
OH
H
OH
Simple Carbohydrates (sugars)
Disaccharides
Maltose
CH2OH
CH2OH
O H
H
O OH
H
H
H
OH H
OH H
HO
H
O
H
OH
H
OH
Glucose
Glucose
-glycosidic bond
Simple Carbohydrates (sugars)
Disaccharides
CH2OH
CH2OH
O H
H
O OH
H
H
H
OH H
OH H
HO
H
O
H
OH
H
OH
Hydrolysis
2
CH2OH
O OH
H
H
OH H
H
HO
H
OH
Glucose
Simple Carbohydrates (sugars)
Disaccharides
Sucrose
CH2OH
O H
H
H
OH H
HO
H
OH
glycosidic bond
O
HOH2C
H
Glucose
O
HO
CH2OH
H
OH
H
Fructose
Simple Carbohydrates (sugars)
Disaccharides
Lactose
CH2OH
O
HO
H
OH H
H
H
OH
H
Galactose
CH2OH
O H
H
H
Glucose
H
OH
O
OH
OH
H
-glycosidic bond
Complex Carbohydrates
Polysaccharides
(glycogen, starches & fibres)
Glycogen – energy storage in animals
Starches – energy storage in plants
Fibres
– provides structure in plants
Complex Carbohydrates
(glycogen versus starches)
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
Animals
Glycogen
Plants
Starch
(amylopectin) and (amylose)
Hydrolysis (breakdown) of
Complex Carbohydrates
Both glycogen and starches can
be broken down by the human
digestive system to give
||
Glucose
©2001 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning ™ is a trademark used herein under license.
Major sources
of starch
include grains,
legumes, and
tubers.
Starches
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
Cellulose
O
O
O
O
O
O
O
O
O
O
Starch and cellulose
molecules compared
(small segments)
Starch digestion in the GI Tract
MOUTH: Starches are hydrolysed to
smaller and smaller polysaccharides
by enzymes referred to as
AMYLASE.
STOMACH: AMYLASE is
deactivated due to acidic pH.
SMALL INTESTINE: Pancreatic
AMYLASE break starch
polysaccharides down more and
DISACCHARIDASES break down
disaccharides.
Fiber in the GI Tract
MOUTH: Fibers are mechanically
ripped apart by teeth and moistened.
NO ENZYME BREAKDOWN
STOMACH and SMALL INTESTINE:
NO ENZYME BREAKDOWN
LARGE INTESTINE: Bacterial
enzymes can break down small
amounts of fiber….
FERMENTATION…. CAUSES GAS
Absorption of Monosaccharides
Monosaccharides enter directly into the blood capillaries
Converted to
GLUCOSE
Glucose and Galactose are moved across cell membranes by
ACTIVE TRANSPORT
Fructose moves across my FACILITATED DIFFUSION
The carbohydrates of grains, vegetables, fruits and
legumes supply most of the energy in a healthful diet.
©2001 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning ™ is a trademark used herein under license.
Maintaining
blood glucose
homeostasis
Diabetes
- related to the function of insulin
to regulate glucose levels
Type I
(juvenile diabetes)
Type 2
(adult diabetes)
©2001 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning ™ is a trademark used herein under license.
Foods rich in
starch and fiber
offer many
health benefits.
©2001 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.
Carbohydrates
on Food Labels
Structure of Artificial Sweeteners
O
NH
SO3H
C
NH
Cyclamate
(30 X)
S
O
Saccharin
(450 X)
O
H
N
C H O
O O CH
3
NH2
O
OH
Aspartame
(180 X)
Hydrolysis of Aspartame
H
NH2
O
N
OH
C H O
O O CH
3
H
NH2
N H
C H
O OH
phenylalanine
HO
OH
O
CH3OH
methanol
O
aspartic acid
Sucralose
(600 X)
Sucrose
CH2OH
O H
H
H
OH H
HO
Glucose
H
OH
CH2OH
O H
Cl
H
OH H
O
O
HOH2C
Fructose
Cl
O
H
HO
CH2OH
H
OH
H
H
OH
CH2 O
H
HO
CH2 Cl
H
OH
H
H
C O
H C OH
HO C H
H C OH
CH2OH
Sugar
Replacers
xylose
H
H C OH
H C OH
HO C H
H C OH
CH2OH
xylitol
H
H
C O
C O
H C OH
HO C H
HO C H
HO C H
H C OH
H C OH
H C OH
H C OH
CH2OH
CH2OH
glucose
mannose
H
H
H C OH
H C OH
HO C H
H C OH
HO C H
HO C H
H C OH
H C OH
H C OH
H C OH
CH2OH
CH2OH
sorbitol
mannitol
©2001 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning ™ is a trademark used herein under license.
Dental
Caries
(cavities)