2. Carbohydrate; Definitions and Classification; Monosaccharides;
Chirality in Monosaccharides; Fischer Projection Formulas and
D,L-Sugars; The Cyclic Hemiacetal Structures of Monosaccharides;
Anomeric Carbons; Mutarotation; Pyranose and Furanose
Structures; Conformations of Pyranoses; Disaccharides; Maltose;
Cellobiose; Lactose; Sucrose; Glycosidic bonds; Formation of
glucosides from monosaccharides; Polysaccharides; Other
Polysaccharides.
3. DEFINING CARBOHYDRATES
Carbohydrates or Saccharides
(Greek Sakcharon meaning "Sugar")
Organic compounds composed of Carbon,
Hydrogen and oxygen.
Many Carbohydrates also contain Nitrogen and
other elements.
4. Carbohydrates derive their name from a
Misleading Concept
'Hydrates of Carbon’
Hydrogen and Oxygen in Carbohydrates were
found to be present in the same proportion as in
water. (2:1).(E.g. Glucose C6H12O6 or C6
(H2O)6).
It is due to this fact that compounds derived
their name “Carbon Hydrate”.
6. This term is not a perfect derivation as many
carbohydrates do not have the same
proportion as water.
Example: DEOXYRIBOSE (C5H10O4)
H-C=O
H-C-H
H-C-OH
H-C-OH
CH2OH
7. CHEMICAL DEFINITION OF
CARBOHYDRATES
Polyhydroxyl: Having more than one
hydroxyl group.
(-OH)
Functional Group: It is a specific group of
atoms or bonds which are part of a larger
hydrocarbon chain.(Provide a specific
chemical behaviour).
8. For carbohydrates, the functional group is the
carbonyl group which may be either
Aldehyde Group (H-C=O)
Or
Keto Group (C=O)
9. WHAT IS SIMILAR & DIFFERENT
IN THESE TWO STRUCTURES?
H-C=O
H-C-OH
OH-C-H
H-C-OH
CH2OH
CH2OH
C=O
OH-C-H
H-C-OH
CH2OH
More than one hydroxyl group in both
10. WHAT IS COMMON & DIFFERENT
IN THESE TWO STRUCTURES?
H-C=O
H-C-OH
OH-C-H
H-C-OH
CH2OH
CH2OH
C=O
OH-C-H
H-C-OH
CH2OH
Carbonyl Group in both But?
11. What is common & different
in these two Structures?
H-C=O
H-C-OH
OH-C-H
H-C-OH
CH2OH
CH2OH
C=O
OH-C-H
H-C-OH
CH2OH
Aldehyde in 1 and Ketone in 2
14. No! But
Hydrolysis
of This
Compound
Yields Two
Compounds
with
Aldehyde Or
Ketone
Groups
H-C
O
H-C-OH
OH-C-H
H-C-OH
H-C-OH
CH2OH
CH2OH
C
OH-C-H
H-C-OH
H-C-OH
CH2OH
HOH
15. No! But
Hydrolysis
of This
Compound
Yields Two
Compounds
with
Aldehyde Or
Ketone
Groups
H-C
O
H-C-OH
OH-C-H
H-C-OH
H-C-OH
CH2OH
CH2OH
C
OH-C-H
H-C-OH
H-C-OH
CH2OH
HOH
=O
O=
16. Many Polyhydroxy Alcohols may Not
have an active Aldehyde or Ketone
Group But they May Yield
Them On Hydrolysis. They
Are Also Designated as
Carbohydrates.
17. THEREFORE, THE COMPLETE
DEFINITION OF CARBOHDRATES IS:
CARBOHYDRATES ARE
POLYHYDROXYL ALCOHOLS WITH
POTENTIALLY ACTIVE CARBONY
GROUPS WHICH MAY BE EITHER
AN ALDEHYDE OR KETONE GROUP.
THEY ALSO CONTAIN THOSE
COMPOUNDS, WHICH YIELD THEM
ON HYDROLYSIS.
19. MONOSACCHARIDES
Monosaccharides are those
carbohydrates which Cannot be
Hydrolyzed further into more simple
carbohydrates.
Thus, they are the Simplest form of
Carbohydrates.
Familiar examples are:
Glucose, Fructose, Ribose & Galactose.
20. Monosaccharides are further classified on the
basis of:
• Aldehyde or Ketone Group:
- Aldomonosaccharides (Aldoses).
- Ketomonosaccharides (Ketoses).
• Carbon Chain Length.
- Trioses.
- Tetroses.
- Pentoses.
- Hexoses.
- Heptoses.
25. GLYCERALDEHYDE IS THE SIMPLEST
MONOSACCHARIDE(PARTICULARLY
ALDOSES)
IT CANNOT BE HYDROLYZED
FURTHER.
IT IS THE SMALLEST POSSIBLE
STRUCTURE THAT IS A
CARBOHYDRATE CANNOT HAVE LESS
THAN 3 CARBON ATOMS.
GENERAL FORMULA OF
MONOSACCHARIDE: (C•H2O)N
(WHERE N IS ANY NUMBER OF THREE
OR GREATER)
26. isomerism
Isomers are basically molecules that have
the same chemical formula but they differ in
their chemical structures.
Asymmetric Carbon is an important
determinant of Isomerism.
Asymmetric Carbon is that Carbon which is
attached with four different groups.
28. The assignment of D or L is made according to
the orientation of the Penultimate Carbon
H
OH L-Sugar : D-Sugar
If the Hydroxyl Group is on the right
the molecule is a D sugar,
Otherwise It is an L sugar.
30. epimerism
Isomers which differ from each other only
with regard to oh group on a single
asymmetric carbon atom.
31. Optical isomers
When a beam of polarized light is passed
through sugars, they will be rotated either
towards right or left.
Right Rotation (dextrorotatory) E.g. D-
Glucose
Left Rotation (levorotatory) E.g. D-Fructose
33. Oxidation Products (Sugar Acids)
When oxidized under proper conditions, Aldoses
may form three types of acids (Sugar Acids):
• Uronic Acids.
• Aldonic acids.
• Saccharic Acids.
Type of sugar Acid produced depends on which
carbon is oxidized.
37. Examples of Aldoses with their Corresponding
Uronic Acids are:
Sugar
Glucose
-------------
Mannose
-------------
Uronic Acids
Glucuronic acid,
Iduronic acid
----------------------
Mannuronic acid
----------------------
38. Examples of Aldoses with their Corresponding
Aldonic Acids are:
Sugar
Glucose
-------------
Mannose
-------------
Galactose
-------------
Aldonic Acids
Gluconic acid
----------------------
Mannonic acid
----------------------
Galactonic acid
------------------------
39. Amino Sugar:
Substitution of Amino
Group for a Hydroxyl Group
of a Sugar Results in the
Formation of an Amino
Sugar.
The Amino Group is
attached to Carbon 2.
H-C=O
H-C-OH
OH-C-H
H-C-OH
H-C-OH
CH2OH
NH2
40. Sugar Alcohols are the Hydrogenated forms of
the Aldoses or Ketoses
H- C=O + H2
H-C-OH
OH-C-H
H-C-OH
H-C-OH
CH2OH
Glucose
CH2OH
H-C-OH
OH-C-H
H-C-OH
H-C-OH
CH2OH
Sorbitol
41. General Comments
Carbohydrates often written as “COH”
much of what we need to know about them, besides
their structure, was covered in “Bioenergetics, Parts
1&2”
here, we cover structure
42. Carbohydrates：
Polyhydroxy aldehydes or ketones, or substances that yield such
compounds on hydrolysis. some also contain nitrogen, phosphorus, or
sulfur.
• (CH2O)n
• 70-80% human energy needs (US~50%)
• >90% dry matter of plants
• Monomers and polymers
• Functional properties
– Sweetness
– Chemical reactivity
– Polymer functionality
43. 3-9 carbon atom sugars
-(pentoses 5, hexoses 6 most common in plants)
have to be obtained by chemical reactions
only a few are free in plant
-many as polysaccharides
Monosaccharides
45. Nomenclature
Ketone Aldehyde
4 Tetrose Tetrulose
5 Pentose Pentulose
6 Hexose Hexulose
7 Heptose Heptulose
8 Octose Octulose
Number
of
carbons
Functional group
46. Carbohydrate Structure
Basic chemical structure consists of sugar units
found as aldehydes or ketones derived from
polyhydric alcohols
contain: C, H, O
often shown as aliphatic or linear structures, but
exist in nature as ringed structures
49. Carbohydrate Classification
Usually by the number of sugar units in the molecule:
• monosaccharides (glucose)
• disaccharides (2 units)
- maltose (2 glucose units)
- sucrose (glucose + fructose)
• polysaccharides (long chain polymers of
monosaccharides
• most important polysaccharides to animals are starch
and cellulose
51. Carbohydrate Classification
Usually by the number of sugar units in the molecule:
• monosaccharides (glucose)
• disaccharides (2 units)
- maltose (2 glucose units)
- sucrose (glucose + fructose)
• polysaccharides (long chain polymers of
monosaccharides
• most important polysaccharides to animals are starch
and cellulose
52. Oligosaccharides
Composed of a few monosaccharide units by glycosidic
link from C-1 of one unit and -OH of second unit
13, 14, 1 6 links most common but 1 1 and 1
2 are possible
Links may be a or b
Link around glycosidic bond is fixed but anomeric
forms on the other C-1 are still in equilibrium
55. Polysaccharides
Polysaccharides are complex carbohydrates made up
linked monosaccharide units.
• Nomenclature:
Homopolysaccharide-a polysaccharide is made up of one type of
monosaccharide unit
Heteropolysaccharide-a polysaccharide is made up of more
than one type of monosaccharide unit
• Starch and glycogen are storage molecules
• Chitin and cellulose are structural molecules
• Cell surface polysaccharides are recognition molecules
56. Sources of Polysaccharides
Microbial fermentation
Higher plants
• seeds
• tree extrudates,
• marine plants,
Chemical modification of other polymers
Polisaccharides
57. Some types of polysaccharides
1.Starch
Starch is a storage compound in
plants, and made of glucose units
It is a homopolysaccharide made
up of two components: amylose
and amylopectin.
Most starch is 10-30% amylose
and 70-90% amylopectin
58. Amylose – a straight chain structure formed by 1,4
glycosidic bonds between α-D-glucose molecules.
H O
OH
H
OH
H
OH
CH2OH
H
O H
H
OH
H
OH
CH2OH
H
O
H
H H O
O
H
OH
H
OH
CH2OH
H
H H O
H
OH
H
OH
CH2OH
H
OH
H
H O
O
H
OH
H
OH
CH2OH
H
O
H
1
6
5
4
3
1
2
amylose
Structure of Amylose Fraction of Starch
59. • The amylose chain forms a
helix.
• This causes the blue colour
change on reaction with
iodine.
• Amylose is poorly soluble in
water, but forms micellar
suspensions
Amylose
60. Amylopectin-a glucose polymer with mainly α -(14)
linkages, but it also has branches formed by α -(16)
linkages. Branches are generally longer than shown above.
H O
OH
H
OH
H
OH
CH2OH
H
O H
H
OH
H
OH
CH2OH
H
O
H
H H O
O
H
OH
H
OH
CH2
H
H H O
H
OH
H
OH
CH2OH
H
OH
H
H O
O
H
OH
H
OH
CH2OH
H
O
H
O
1 4
6
H O
H
OH
H
OH
CH2OH
H
H H O
H
OH
H
OH
CH2OH
H
H
O
1
OH
3
4
5
2
amylopectin
Structure of Amylopectin Fraction of Starch
61. Amylopectin causes a
red-violet colour change
on reaction with iodine.
This change is usually
masked by the much
darker reaction of
amylose to iodine.
Amylopectin
Amylopectin
62. 2 Glycogen
Storage polysaccharide in animals
Glycogen constitutes up to 10% of liver mass and 1-2% of
muscle mass
Glycogen is stored energy for the organism
Similar in structure to amylopectin, only difference from
starch: number of branches
Alpha(1,6) branches every 8-12 residues
Like amylopectin, glycogen gives a red-violet color with
iodine
64. 3 Cellulose
The β-glucose molecules are joined by condensation, i.e. the removal of
water, forming β-(1,4) glycosidic linkages.
Note however that every second β -glucose molecule has to flip over to
allow the bond to form. This produces a “heads-tails-heads”
sequence.
The glucose units are linked into straight chains each 100-1000 units
long.
Weak hydrogen bonds form between parallel chains binding them into
cellulose microfibrils.
Cellulose microfibrils arrange themselves into thicker bundles called
microfibrils. (These are usually referred to as fibres.)
The cellulose fibres are often “glued” together by other compounds such
as hemicelluloses and calcium pectate to form complex structures such
as plant cell walls.
68. • Source: Cell walls of higher plants (citrus rind)
• Structure: Largely a linear polymer of polygalacturonic acid with varying
degrees of methyl esterification. (Also some branches –HAIRY REGIONS)
– >50% esterified is a high methoxy (HM) pectin
– <50% esterified is a low methoxy (LM) pectin
• Functional Properties:
Main use as gelling agent (jams, jellies)
– dependent on degree of methylation
– high methoxyl pectins gel through H-bonding and in presence of sugar
and acid
– low methoxyl pectins gel in the presence of Ca2+ (‘egg-box’model)
Thickeners
Water binders
Stabilizers
