Carbohydrates
L. Noha Soliman
Carbohydrates
Objectives
 Introduction.
 Functions Of Carbohydrates.
 Types Of Carbohydrates.
 Classification Of Carbohydrates.
 MONOSACCHARIDES
• Monosaccharide Classification.
• Some important monosaccharides and their
structures.
• Sugars exhibit various forms of isomerism
 DISACCHARIDES
 POLYSACCHARIDES
Introduction
 Also called saccharides , which means “sugars.”
 They composed of carbon, hydrogen, and oxygen in a 1:2:1
empirical ratio.
 The general empirical formula for a carbohydrate is CH2O.
 If a carbohydrate has 5 carbons atoms, what would be its
C5H10O5
empirical formula?
 If a carbohydrate has 12 hydrogen atoms present, what would
be its empirical formula?
C6H12O6
 All carbohydrates have this empirical
formula except deoxy sugars, amino sugars.
 Most carbohydrates end with the suffix –ose.
Introduction
 Are produced by photosynthesis in plants.
 Such as glucose are synthesized in plants from CO2, H2O, and light
energy from the sun.
 Are oxidized in living cells (respiration) to produce CO2, H2O, and
energy.
Functions of
Carbohydrates
 Provide energy source:
• Living things use carbohydrates as their main source of
energy.
• The breakdown of sugar supplies immediate energy for all
cell activities.
 Provide energy storage:
• Plants store energy in a complex carbohydrate form called
starch.
• Animals store energy in a complex carbohydrate in their
muscle tissue and liver in the called glycogen.
Functions of
Carbohydrates
 Structural Building Material:
• Plants and some animals also use
carbohydrates for structural purposes.
• Plants build their cell walls of a
complex carbohydrate called cellulose.
• Animals such as arthropods build their
exoskeletons of a complex carbohydrate
called chitin.
• Chitin is also found in the cell walls of
Fungi.
Carbohydrates are chains (polymers) made of monomers.
The most common monomer of carbohydrates is…
There are
2 types
of
carbohydrates
Simple
Complex
Simple Sugars are carbohydrates made up of 1
or 2 monomers.
They taste sweet.
Complex Cabohydrates are polymers made up
of many monomers.
Most taste starchy.
Classes of Carbohydrates
Classifications based on
number of sugar units in total
chain:
Monosaccharides - single sugar unit
Disaccharides - two sugar units
Oligosaccharides- 3 to 10 sugar units
Polysaccharides- more than 10 units
Classes of Carbohydrates
MONOSACCHARIDES
The basic building blocks (monomers) of carbohydrates.
(cannot be further hydrolyzed into smaller units).
Known as simple sugars.
Readily soluble in water.
Same no. of C as O atoms.
Have the general formula (CH2O)n
They contain:
– a carbonyl group (C=O)
1
2
– either at C atom or at the C atom
– multiple hydroxyl groups (-OH)
White crystalline solids.
e.g. Glucose is C6H12O6
Structural representation
of sugars
 Fisher projection: straight chain form.
 Haworth projection: simple ring.
 Chair form.
α- D-Glucose
D-Glucose
α- D-Glucose
Monosaccharide
Classification
MONOSACCHARIDE
FUNCTIONAL
GROUP
NUMBER OF CARBONS
IN THE BACKBONE
ALDOSE
TRIOSE
KETOSE
PENTOSE
HEXOSE
Monosaccharide
Classification
Classified by number of carbons:
3C = triose (glyceraldehyde)
5C = pentose (ribose)
6C = hexose (glucose)
H
CH2OH
H
HO
CH2OH
O
H
OH
6
H
Glucose
H
OH
OH
C
O
H
HO
H
5
OH
O
H
HO
H
Ribose
H
H
H
C
OH
C
3OH
H
Glyceraldehyde
Monosaccharide
Classification
TRIOSES
PENTOSES
HEXOSES
contains 3 carbon atoms
contains 5 carbon atoms
contains 6 carbon atoms
C 3 H6 O3
C5H10O5
C6H12O6
ribose
deoxyribose
glucose
immediate source of
energy for cellular
respiration
glyceraldehydes
dihydroxyacetone
building blocks to form
larger molecules
components of nucleic
acids
galactose
sugar found in milk and
yogurt
fructose
sugar found in honey
Monosaccharide
Classification
It can be classified based on functional group
(According to where the carbonyl group is located):
• Aldose - polyhydroxyl aldehyde (aldehyde sugar):
with the carbonyl group (C=O) at the first carbon position, which
forms an aldehyde group (CHO).
• Ketose - polyhydroxyl ketone (ketone sugar):
Carbonyl group is at C2 position.
1
1
2
2
Monosaccharide
Classification
Both functional group have reducing properties
~ reducing sugars
ALDOSES
KETOSES
carbonyl group (C=O) at 1C carbonyl group (C=O) at 2C
is the aldehyde group
is the ketone group
sugar is known as aldose
(aldehyde sugar)
sugar is known as ketose
(ketone sugar)
glucose
fructose
Monosaccharide
Classification
Learning check
Identify each as aldo- or keto- and as
tetrose, pentose, or hexose:
O
C H
CH2OH
H C OH
C O
H C OH
HO C H
H C OH
H C OH
H C OH
CH2OH
CH2OH
Aldohexose
Ketopentose
Some important
monosaccharides
 Glucose:
•
•
•
•
In plants and fruits.
Mild sweet flavor.
known as blood sugar.
Essential energy source.
 Fructose:
• Sweetest sugar
• Found in fruits and honey.
• Added to soft drinks, cereals, deserts.
 Galactose:
• Part of milk sugar.
• Hardly tastes sweet.
• Rarely found naturally as a single sugar.
Some important
monosaccharides
 Glyceraldehyde
Simplest sugar
 Ribose
Found in RNA
 Deoxyribose
Found in DNA
Glyceraldehyde
1. Aldose – Ketose
Isomerism: (Isomers)
 They are molecules which have the same molecular formula but
have different structures.
 Glucose and fructose both have the empirical formula C6H12O6
but they have different structural formulas or shapes.
Chiral center
•Asymmetric carbon:
4 different things are attached to it.
•You must have at least one asymmetric
carbon to have stereoisomers.
Cl
|
I- C - F
|
Br
H
|
C=O
|
H-C-OH
|
CH2OH
Glyceraldehyde
Chiral center
Chiral
center
Physical properties
• Optical activity
ability to rotate plane polarized light.
• Dextrorotatory
- rotate to right
- use + symbol
- usually D isomers
• Levorotatory
- rotate to left
- use - symbol
- usually L isomers
Light is passed through a
polarized filter.
A solution of an optical
isomer will rotate the
light one direction.
2. D and L Isomerism:
(Enantiomers)
• Pairs of structures that are mirror images of each other and
CANNOT be superimposed on each other.
• Designated by D- or L- at the start of the name.
2. D and L Isomerism:
(Enantiomers)
O
H
C
H – C – OH
HO – C – H
H – C – OH
H – C – OH
CH2OH
D-glucose
O
H
C
HO – C – H
H – C – OH
HO – C – H
HO – C – H
CH2OH
L-glucose
3. Epimers:
•
Two sugars that differ in configuration at only one chiral center.
• The most important epimers of glucose are:
Mannose
epimerization at C2
Galactose
epimerization at C4
Hemiacetal & hemiketal
formation:
An aldehyde can
react with an
alcohol to form a
hemiacetal.
A ketone can react
with an alcohol to
form a hemiketal.
H
C
H
O
+
R'
OH
R'
O
R
OH
R
aldehyde
alcohol
hemiacetal
R
C
C
R
O
+
"R
OH
R'
ketone
"R
O
C
R'
alcohol
hemiketal
OH
4. Pyranose and Furanose
ring structures:
 Pentoses and hexoses can
cyclize as the ketone or
aldehyde reacts with a
distal OH.
1
H
HO
H
H
 Glucose forms an intramolecular hemiacetal, as
the C1 aldehyde & C5
OH react, to form a 6member pyranose ring.
2
3
4
5
6
CHO
C
OH
C
H
C
OH (linear form)
C
OH
D-glucose
CH2OH
6 CH2OH
6 CH2OH
5
H
4
OH
H
OH
3
H
O
H
H
1
2
OH
-D-glucose
OH
5
H
4
OH
H
OH
3
H
O
OH
H
1
2
OH
-D-glucose
H
4. Pyranose and Furanose
ring structures:
Fructose forms either
• A 6-member pyranose ring, by reaction of the C2 keto group with
the OH on C6, or
• A 5-member furanose ring, by reaction of the C2 keto group with
the OH on C5.
CH2OH
1
HO
H
H
2C
O
C
H
C
OH
C
OH
3
4
5
6
HOH2C 6
CH2OH
D-fructose (linear)
H
5
H
1 CH2OH
O
4
OH
HO
2
3
OH
H
-D-fructofuranose
5. Alpha and beta
anomers:
 Cyclization of glucose produces a new asymmetric center at C1.
 The 2 stereoisomers are called anomers,  & .
GLUCOSE
primary source of energy
 - glucose
 - glucose
hydroxyl (-OH) group of the 1C projects hydroxyl (-OH) group of the 1C projects
below
the upward
the plane
plane of the ring
of the ring
DISACCHARIDES
These are formed when two monosaccharide molecules join together
with the elimination of one molecule of water.
They have the general formula C12H22O11.
C6H12O6
Glucose
+ C6H12O6 =
+ Glucose =
C12H22O11 + H2O
Maltose + Water
Sweet tasting.
Water soluble.
EXAMPLE:
Maltose
Sucrose
Lactose
Disaccharide Formation
Disaccharides are formed when two monosaccharides are joined by
dehydration synthesis reaction.
GLUCOSE + GLUCOSE -> Maltose (malt sugar)
GLUCOSE + FRUCTOSE -> Sucrose (cane sugar)
GLUCOSE + GALACTOSE -> Lactose (milk sugar)
CH2OH
H
CH2OH
O H
H
CH2OH
O H
H
CH2OH
O H
H
O H
H20
+
O
OH
α- GLUCOSE
OH
HO
α- GLUCOSE
OH
OH
OH
MALTOSE
Dehydration Synthesis
• Building reaction.
• H2O is removed in order to form a new bond.
Hydrolysis Reaction
• Breaking reaction.
• H2O is required to break a bond.
Glycosidic linkage
• The bond between monosaccharides.
• What type of reaction would form this bond?
– Dehydration synthesis reaction.
• What kind of bond is a glycosidic linkage?
OH
– Polar covalent bond.
OH
H2 C
H 2C
O
OH
O
C
HO
OH
OH
OH
HO
HO
HO
OH
OH
H2 C
H2 C
O
OH
HO
O
C
OH
O
HO
HO
+ H2O
OH
Disaccharide Formation
Some important
disaccharides
• Sucrose: Saccharose or table sugar
• It is fructose and glucose combined.
• Source of sucrose is sugar beets and sugar cane.
• Tastes sweet, and is readily available.
• brown, white, powdered.
Some important
disaccharides
• Maltose: Malt sugar
•
•
•
•
Consists of two glucose units.
Produced when starch breaks down.
Not abundant.
Present in germinating seeds.
Lactose: milk sugar
• Glucose and galactose.
• Main carbohydrate in milk.
Some important
disaccharides
OLIGOSACCHARIDES
• Oligosaccharide is a few linked monosaccharides
and are at time associated with proteins
(glycoproteins) or lipids (glycolipids).
POLYSACCHARIDES
Polysaccharides are chains of monosaccharides that have been
joined by many dehydration synthesis reactions.
Do not taste sweet and do not crystallize.
Insoluble in water.
Form colloidal solutions when
added to water.
Polysaccharide diversity
 Molecular structure determines function.
 The function of the polysaccharide depends on what type of
isomer of glucose the polysaccharide is made.
 Storage Polysaccharides
Energy storage - starch and glycogen.
 Structural Polysaccharides
Used to provide protective walls to cells – cellulose and chitin.
In starch
In cellulose
Some important
polysaccharides
Starch
 Energy storage used by plants.
– Storage form of glucose in plants.
– Found in grains, tubers, and legumes.
 Body hydrolyzes plant starch to glucose.
 Long repeating chain of α-D-glucose.
 Chains up to 4000 units.
Starch
 Starch consists of two compounds:
– Amylose: straight chain of α-D- glucose, major form of starch.
– Amylopectin: branched chains of α-D-glucose.
Glycogen
 Energy storage of animals:
– Storage form of glucose in the body.
– Provides a rapid release of energy when needed.
 Structure is similar to amylopectin but more branches.

Made from α-glucose.
Glycogen
 Found mainly in liver and muscle cells.
 When
the level of glucose in your blood runs low, glycogen is
released from your liver.
 The
glycogen stored in your muscles supplies the energy for
muscle contraction and thus, for movement.
carbon and energy (glucose) storage molecules
more branching
Some important
polysaccharides
Cellulose
 Most abundant organic
compound on Earth.

It forms the main part of the
cell wall in plants cells.

Cellulose is the major
component of cotton , wood
and paper.
Cellulose
 It is a polysaccharide of β glucose units in
unbranched chains.
 Linked by β-1,4 glycosidic bonds.
6
5
4
 Each β-glucose related to the next by a
rotation of 180°.
1
4
1
4
1
3
1
4
2
Cellulose
Every other glucose is flipped over, due to β linkages.
 This promotes intra-chain and inter-chain H-bonds and van der
Waals interactions, that cause cellulose chains to be straight & rigid,
and pack with a crystalline arrangement in thick bundles microfibrils.
Digesting
starch vs. cellulose
starch
easy to
digest
cellulose
hard to
digest
enzyme
enzyme
Digesting
starch vs. cellulose
Cow
can digest cellulose well;
no need to eat other sugars
Gorilla
can’t digest cellulose well; must
add another sugar source, like
fruit to diet
Amino derivatives
 The replacement of a hydroxyl group on a carbohydrate results in an
amino sugar.
CH2OH
CH2OH
O
H
H
OH
OH
H
OH
H
H
OH
H
OH
-D-glucose
O
H
OH
H
H
OH
H
NH2
-D-2-aminoglucose
(glucosamine)
•Uses for amino sugars.
•Structural components of bacterial cell walls.
•As a component of chitin.
•A major structural unit of chondroitin sulfate - a component of cartilage.
•Component of glycoprotein and glycolipids.
Chitin
It is the “plastic-like” material that composes the
exoskeletons of arthropods (insects, arachnids, and
crustaceans).
Most fungi (mushrooms) have chitin present within their
cell walls.
Chitin
Similar to cellulose but the hydroxyl group on each
monomer substituted with an acetyl amine group.
 Cellulose strands are parallel, chitins can be parallel or
antiparallel.
Above is a structural
monomer of chitin.