2. Carbohydrates
Nomenclature of monosaccharaides
Generally carbohydrates have been given none-systemic
name
1. The number of carbon as the variable prefix
followed by –ose as the suffix
2. Carbones are numbered from the top of the
sugar
3. Aldehyde or ketone group is on the carbon
with the lowest possible number
4. A chiral carbon
3. Monosaccharides
A chiral carbon or asymmetric carbon: is a carbon atom
attached with four different groups and it determines the
number of isomers of sugar and optical activity
4. Monosaccharides
The number of possible isomers of any given sugar
depends on the number of asymmetric carbon
atoms in this sugar and can be calculated by Vant
Hoff’s rule:
The number of possible isomers =2n where n =
number of asymmetric carbon
Glucose, with four asymmetric carbon atoms, can
form 16 isomers
5.
6. Monosaccharides
Isomers
Are molecules with the same molecular formula but
different chemical structures which means they
contain the same number of atoms of each element,
but have different arrangements of their atoms in
space.
7. Monosaccharides
Cyclic (ring) structure of monosaccharides
Hawarth projection formula
All monosaccharides with at least four carbon
atoms exist predominantly as cyclic structure
Ring formation occurs in aqueous solution as
aldehyde group (C1 in aldose) and ketone group (C2
in ketose) react reversibly with hydroxyl group (C4
orC5) in the same sugar to form hemiacetal
8. Monosaccharides
o The ring structure of an aldose is a hemiacetal,
since it is formed by combination of an aldehyde
and an alcohol group
o The ring structure of a ketose is a hemiketal
Crystalline glucose is α-D-glucopyranose. The cyclic
structure is retained in solution, but isomerism
occurs about position 1, the carbonyl or anomeric
carbon atom, to give a mixture of α-glucopyranose
(38%) and β-glucopyranose (62%)
`
12. Monosaccharides
Cyclic hemiacetal with five membered ring called
Furanose ( Furan)
Cyclic hemiacetal with six membered ring called
Pyranose (Pyran)
13. Chair and boat forms
Chair and boat structure formation occurs as the
Haworth formula
A chair and boat forms are more accurate
representation of the bond angels of the molecules
chair form is more stable than boat form
15. Monosaccharides isomers
Sugars Exhibit Various Forms of Isomerism.
(1) D and L isomerism(Enantiomers):
Enantiomers are a type of isomers designated as “D”
and “L” isomers that are mirror images of each other
and differ in the configuration around the
asymmetric carbon before the last carbon atom. e.g
D and L glucose
17. Monosaccharides isomers
Sugars Exhibit Various Forms of Isomerism.
(2) Pyranose and furanose ring structures:
The stable ring structures of monosaccharides are
similar to the ring structures of either pyra or furan
For glucose in solution, more than 99% is in the
pyranose form
18. Monosaccharide isomers
(3) Alpha and beta anomers
In cylic formula the carbonyl group becomes asymmetric
carbon and called anomeric carbon α-Glucose and β-
Glucose called anomers (anomers are isomers obtained
from the change of position of hydroxyl group attached
to the anomeric carbon of the same sugar
If the –OH group is below the plane of the ring it is
called alpha sugar (α)
If the –OH group is above the plane of the ring it is
called beta sugar (β)
20. Monosaccharide isomers
(4) Epimers: Isomers differing as a result of variations
in configuration of the -OH and -H on carbon
atoms 2, 3, and 4 of glucose
the differ in the position of (OH) group at only one of
their asymmetric carbon atom other than before the last
( sub-terminal) carbon
21. Monosaccharide isomers
Biologically, the most important epimers of glucose are
mannose and galactose, formed by epimerization at
carbons 2 and 4, respectively
D-Glucos and D-Galactose are C4 epimers
D-Glucose and D-Mannose are C2 epimers
D-arabinose is an epimer of D-ribose at C2
D-xylose is an epimer of D-ribose at C3
22. CHO
C OH
H
C H
HO
C OH
H
C OH
H
CH2OH
CHO
C H
HO
C H
HO
C OH
H
C OH
H
CH2OH
CHO
C OH
H
C H
HO
C H
HO
C OH
H
CH2OH
Galactose
Glucose Mannose
CHO
C OH
H
C OH
H
C OH
H
CH2OH
CHO
C H
HO
C OH
H
C OH
H
CH2OH
CHO
C OH
H
C H
HO
C OH
H
CH2OH
Xylose
Ribose Arabinose
23. Monosaccharide isomers
(5) Aldose-ketose isomerism: Fructose has the
same molecular formula as glucose but differs in its
structural formula, since there is a potential keto group
in position 2, the anomeric carbon of fructose (Figures
13–4 and 13–7), whereas there is a potential aldehyde
group in position 1, the anomeric carbon of glucose
26. The usefulness of this notation to Fischer, in his carbohydrate studies, is evident in the fol
.
Monosaccharides
Ribose
(Aldopentose)
Ribulose
(Ketopentose))
28. Properties of monosaccharides
Physical properties
1- All monosaccharides soluble in water ,
crystalline, and unaffected by digestive enzymes
2- All monosaccharide have one asymmetric
carbon or more except dihydroxyacetone
3- All monosaccharides have optical activity except
dihydroxyacetone
29. Properties of monosaccharides
Optical Activity
It is the ability of substance which have one
asymmetrical carbon or more to rotate a beam of
polarized light (light which vibrates in only one
direction)
Rotation is either to the right or to the left, If the
rotation is to the right it is called dextrorotatory (+ or
d) and if it is to the left it is known as levorotatory ( -
or l )
31. Properties of monosaccharides
4- Stereoisomerism
5- Enantiomers
6- Epimers
7- Specific rotation
It is the angle of rotation specific for each optically
active substance when polarized light pass
through 1decimeter (10 cm) measuring tube
containing 1g/ml of the substance. e.g., specific
rotation for glucose is (+52.7o)
32. Properties of monosaccharides
Chemical properties
1- Oxidation reactions
2- Reduction reactions
3- Fermintation
4- Osazone formation
5- Esterfication
6- Molish’s reaction
7- Benedict’s reaction
8- Formation of Glycosidic bond
33. Important monosaccharides
D-Glucose (an aldohexose, C6H12O6)
The name glucose comes from the Greek word glukus,
meaning sweet, the suffix “-ose’’ denotes a sugar
Glucose is the most predominant sugar in human
body, it is the major source of energy in mammals
It is the sole source of energy for brain and red blood
cells
It is known as dextrose, blood sugar and grape sugar,
Solution of glucose rotates polarized light to the right
and in Latin dexter means right
34. Important monosaccharides
D-Glucose (an aldohexose, C6H12O6)
it is present in honey and fruits Hydrolysis of starch,
cane sugar, maltose, and lactose
The clinical significant is that it present in the urine
(glycosuria) in diabetes mellitus due to hyperglycemia
36. Important monosaccharides
D-Fructose (Ketohexose, C6H12O6 )
The name fructose comes from the Latin word
fructus, meaning fruit, the suffix “-ose’’ denotes a
sugar
Fructose is the sweetest of monosaccharides, it is
present in honey and fruits
It is the main sugar of semen which used by sperms as
energy source
It is known as fruit sugar and levulose (solution of D-
Fructose rotates polarized light to the left and in Latin
levo means left).
37. Important monosaccharides
D-Fructose (Ketohexose, C6H12O6 )
Can be changed to glucose in the liver and so used
in the body
Clinical sigmificant Hereditary fructose
intolerance leads to fructose accumulation and
hypoglycemia
