carbohydrates biochemistry part one monosaccharides

1. Carbohydrates Chemistry Lec. (1)
Monosaccharaides
By
Dr Dina Aboraya

2. Definition:
▪ Carbohydrates are organic substances
composed of carbon, hydrogen and
oxygen (C, H, O).
▪ Hydrogen and Oxygen are present in
the same ratio as in water (H2O = 2:1),
so called carbohydrates with the
general formula (CH2O) n where n=3 or
more.

3. Characteristics of Carbohydrates
Carbohydrates are organic substances
characterized by 3 features:
1- They are composed of three elements C, H & O
2- Presence of an aldehyde group or ketone group.
➢ If the sugar has an aldehyde group, it is classified
as an aldose.
➢ If it has a ketone group, the sugar is classified as
a ketose.
3- Presence of more than one hydroxyl group (- OH-)
(polyhydroxy).

4. The aldehyde group is always at the end of the
carbon chain,
and the ketone group is always on the second
carbon of the chain

5. Classification of Carbohydrates
On the basis of: Number of structural units into:
• Contain 1 sugar unit, as glucose, fructose.
Monosaccharides
• contain 2 sugar units as sucrose and lactose.
Disaccharides
• Contains 3-10 sugar units as maltotriose and raffinose.
Oligosaccharides
• Contain more than 10 sugar units as starch and cellulose.
Polysaccharides

6. Monosaccharaides
Definition:
• They are the simplest carbohydrate units
which cannot by hydrolyzed into simpler
units.
• Monosaccharaides have the general formula is
CnH2nOn
• Monosaccharaides have the ending ose
(glucose, galactose, etc…).

7. Classification of Monosaccharaides
They are further classified according to :
1 Number of carbon atoms (n) in the sugar:
triose, tetrose, pentose, and hexose.
2 Active group in the sugar:
If its contain aldehyde group …. its called aldose, and
if it contains an ketone group … its called ketose.

8. Examples of monosaccharides
1. Trioses (3C) :
➢ Aldoses (Aldotriose)
e.g. glyceraldehyde
➢ Ketoses (Ketotriose)
e.g. dihydroxyacetone

9. Examples of monosaccharides
2. Tetroses (4C) :
➢ Aldoses (Aldotetrose)
e.g. Erythrose
➢ Ketoses (Ketotetrose)
e.g. Erythrulose

10. Examples of monosaccharides
3. Pentoses (5C) :
➢ Aldoses (Aldopentose)
e.g. Ribose , Arabinose and Xylose
➢ Ketoses (Ketopentose)
e.g. Ribulose and Xylulose

11. Examples of monosaccharides
4. Hexoses (6C) :
➢ Aldoses (Aldohexose)
e.g. Glucose, Mannose, Galactose
➢ Ketoses (Ketohexose)
e.g. Fructose

12. ,Arabinose

13. Chiral carbon atom
(Asymmetric carbon atom)
Definition:
A chiral carbon atom is a carbon atom in a
molecule that attached to four different atoms or
groups .

14. ▪ Glyceraldehyde contains one asymmetric carbon atom
▪ Glucose contains four asymmetric carbon atoms.
▪ All sugars contain asymmetric carbon atom except
dihydroxy acetone.
Chiral carbon atom
(Asymmetric carbon atom)

15. Carbohydrates properties
Any compound having asymmetric carbon
atom shows two properties:
1. Optical Activity.
2. Stereoisomerism.

16. Optical Activity
▪ Definition:
An optically active compound is a compound that
rotates the plane of polarized light to the right or
to the left.
➢ The optical activity property depends on the
presence of asymmetric carbon atom.
➢ All monosaccharaides contain asymmetric carbon
atom except dihydroxy acetone.
➢ All monosaccharaides are optically active except
dihydroxy acetone.

17. Plane polarized light is an ordinary light which its waves
pass in one single plane by the action of special prisms
(Nicols prism).
➢ Compound which rotates the plane polarized light to
the right is called dextrorotatory or (d or +) e.g.
glucose (dextrose), and sucrose
➢ While compound that rotates the plan polarized light
to the left is called levorotatory or (l or -) e.g.
fructose (levulose).
Optical Activity

18. Measurement of optical activity is done by polarimeter which
consists of:
1. Source of light (Na light).
2. Nicol prism (polarizer) which converts the ordinary light to
one single plane.
3. A tube containing the optically active solution.
4. Nicol prism (analyzer) which rotates the plane polarized
light.
Polarimeter

19. Stereoisomers in carbohydrates
Stereoisomers:
Compounds that have the same structural formula but differ in
the spatial configuration i.e. they have the same number of C, H
and O atoms but differ in the arrangement of groups and atoms
in the space.
➢ The number of possible isomers of a compound depends on
the number of asymmetric carbon atoms (n) and equal (2) n
e.g.
➢ Trioses : 1 Asymmetric carbon = 2 1 = 2.
➢ Tetroses : 2 Asymmetric carbon atoms = 2 2 = 4.
➢ Pentoses : 3 Asymmetric carbon atoms = 2 3 = 8.
➢ Hexoses : 4 Asymmetric carbon atoms = 2 4 = 16.
➢ Heptoses : 5 Asymmetric carbon atoms = 2 5 = 32.

20. N.B. The number of asymmetric carbon atoms :
➢ Aldoses= (Number of carbon atoms - 2)
➢ Ketoses= (Number of carbon atoms - 3)
(ketoses is less than aldoses by one)
e.g.:
- Glucose has 4 asymmetric carbons (6 - 2=4)
- Fructose has 3 asymmetric carbons (6 - 3=3)
Number of isomers:
e.g.
➢ Glucose has 4 asymmetric carbons …….. 2 4 =16
➢ Fructose has 3 asymmetric carbons …….. 2 3 = 8

21. 1- D and L
isomers
(enantiomers)
(mirror image)
2- Pyranose
and furanose
ring structure
3- α and
β isomers
(anomers)
4- Epimers

22. 1. Enantiomers (D and L isomers) (mirror image)
➢ They are isomers which are mirror
images of each other e.g. D and L
sugar.
➢ D and L refer to the configuration
of the pre-last carbon (carbon
atom before the last one, i.e.
preterminal).
➢ If the OH attached to the pre-
last C is directed to:
❑Right → D-sugar e.g. D-Glucose
❑Left → L-sugar e.g. L-Glucose.

23. 1. Enantiomers (D and L isomers) (mirror image)
➢ N.B Most sugars in human are in D form except
L-fucose, L-arabinose, L-xylulose and L-iduronic acid.

24. 2- Pyranose and furanose ring structure
They are isomers that differ in the configuration
of the sugar in the cyclic (ring) structure.
Glucopyranose & Glucofuranose.
Fructopyranose & Fructofuranose

25. 3- α and β isomers (anomers)
They are isomers that differ in the position of OH group
around the anomeric carbon.
➢ If OH group is attached below the ring plane (right) , it's
α anomer.
➢ If OH group is attached above the ring plane (left) , it's
β anomer
e.g. α-glucopyranose , β-glucopyranose

26. 4- Epimers
They are isomers that differ in the position of one OH group at
one asymmetric carbon atom only (epimeric carbon
atom).
e.g.
➢ D-glucose and D-mannose at C2 (C2 epimer)
➢ D-glucose and D-galactose at C4 (C4 epimer)

27. SUGAR DERIVATIVES
1. Sugar Acids : Oxidations of monosaccharide
2. Sugar Alcohols : Reductions of monosaccharide
3. Deoxy Sugars : Replacement of OH group with H

28. 1. Sugar Acids
A- Aldonic acid
Oxidation of first (C1)
aldehyde group to carboxylic
group.
e.g.:
( C1 ) of Glucose →
Gluconic acid
N.B.:
- Occur by mild oxidation
- If the first aldehyde
group is free

29. 1. Sugar Acids
B- Uronic acid
Oxidation of the last hydroxyl
group to carboxylic group
e.g.:
( C6 ) of Glucose →
Glucuronic acid
N.B.: If the first aldehyde
group is not free

30. Importance of Glucuronic Acid:
1- Detoxication of toxic compounds by
conjugation.
2- Formation of Mucopolysaccharides
3- Metabolism of bilirubin (conjugation of
bilirubin in the liver to increase its solubility).
4- Excretion of steroids

31. 1. Sugar Acids
C- Aldaric acid
Oxidation of both carbonyl carbon
(C1) and Last hydroxyl carbon (C6)
produces dicarboxylic acid or aldaric
acid (saccharic acid; dicarboxylic acid)
e.g.
Glucose → Glucaric acid
Galactose → Mucic acid
N.B.: Occur by strong oxidation

32. Sugar Acids
Oxidation of the
first aldehyde
group.
ALDONIC ACID
Oxidation of the
last hydroxyl
group.
URONIC ACID
Oxidation of both first
aldehyde group and last
hydroxyl group.
ALDARIC ACID
D-glucose (by weak
oxidizing agents)
D-gluconic acid
D-glucose (by
enzymes)
D-glucuronic acid
D-glucose (by
strong oxidizing
agents)
D-glucaric acid

33. They are the products of Reduction of monosaccharide.
2. Sugar Alcohol (Alditol)

34. Inositol (cyclitol)
➢ Its cyclic alcohol derived from glucose.
➢ A member of vitamin B complex.
Function:
1) It is the main muscle sugar (myoinositol).
2) It enters in the formation of phosphatidyl inositol
(phospholipid) which is a platelet activating factor and also
needed as a second messenger in the mechanism of hormone
action.
2. Sugar Alcohol (Alditol)

35. 3. Deoxy Sugars
Definition: They are monosaccharides with one hydroxyl group
replaced by hydrogen, i.e. there is one oxygen missed.
Examples:
➢ If the sugar is pentose (at carbon 2) e.g. ribose which gives
deoxyribose (component of DNA).
➢ If the sugar is hexose (at carbons 6) e.g. L-galactose which
gives L-fucose (component of glycoprotein).

36. Biological Importance of Monosaccharaides

37. Biological Importance of Monosaccharaides
Galactose

38. Biological Importance of Monosaccharaides