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Proteins

Maintenance of structures

Proper functioning of all
living organisms
Biological functions of proteins
•
•
•
•
Enzymes - Catalyze biological processes e.g. Pepsin
Hormones - Regulate body processes e.g. Insulin
Storage proteins - Store nutrients e.g. Ferritin
Transport proteins - Transport oxygen and other
substances through the body e.g. Haemoglobin
• Structural proteins - Form an organism’s structure
e.g. Collagen
• Protective proteins - Help fight infection e.g. Antibodies
• Contractile proteins - Form muscles
e.g. Actin and myosin
Structure of Proteins
• The building units of proteins are called amino acids
• All naturally occurring amino acids are -amino acids
O

H2N
CH
H
C
OH
• Most proteins are formed from some twenty common
amino acids, linked up by peptide bonds
H
H
O
N
C
C
H
R
H
H
+
OH
H
O
N
C
C
H
R
H
O
N
C
C
H
R'
Peptide linkage
H
O
N
C
C
OH
H
R'
+
H2O
OH
• Hydrolysis of proteins
• Separation of amino acids by paper chromatography
Linked with
1. Phase equilibrium - Application of partition
2. Chemistry of amino acids
Carbohydrates
• As a source of energy
Glycogen in animals, Starch in plants
• General formula CxH2yOy
• Synthesized by photosynthesis
6CO2(g) + 6H2O(l)
light
chlorophyll
C6H12O6(s) + 6O2(g)
Classification of Carbohydrates
• Monosaccharides - (CH2O)n where n>2
E.g.
C6H12O6
Hexose (most important)
C5H10O5
Pentose
H
O
1
CH 2OH
C
H
C
OH
HO
C
H
H
C
OH
H
C
OH
CH 2OH
Aldohexose
Glucose
2C
O
HO
C
H
H
C
OH
H
C
OH
CH 2OH
Ketohexose
Fructose
•
Disaccharides
- C12H22O11
•
E.g. Maltose, Sucrose
Polysaccharides
- (C6H10O5)n where n is a very large number
E.g. Starch, Cellulose
Open chain and cyclic structures of glucose and fructose
H OH
H
1
+
O
6
C
H
5
O
HO
H
C
OH
1
HO
H
HO
C
OH
H
H
H
H
C
5
C
H
OH
-glucose
OH
H OH
..
OH
CH 2OH
(Fischer projection)
6
5
HO
H
O
1
HO
H
H
OH
OH
-glucose
H
•
The cyclic structures are more stable than
the open chain structure
•
The lone pair on -OH can attack the
carbonyl carbon from above or below the
plane leading to the formation of two
isomers ( and  glucose).
6
HOH 2C
1 CH 2OH
O
1 CH 2OH
2
+ C
H
5
OH
O
H
HO
H
H
C
2
OH
H
C
OH
5
C
..
OH
6CH OH
2 ..
Fructose
H
HO
-furanose
H
H
6
OH O
HO
1
CH2OH
H
H
OH
H
2
OH
-pyranose

In the free state, fructose exists as
pyranose (6-membered ring).
 In disaccharides and
polysaccharides, fructose exists as
furanose (5-membered ring).
Disaccharides and Glycosidic linkage
Condensation
2C6H12O6
hydrolysis
C12H22O11 + H2O
Glucose + Glucose
Maltose + water
Glucose + Fructose
Sucrose + water
H OH
H OH
4
H
O
HO
1
HO
H
H
H
H
OH
-glucose
O
HO
+
H
HO
H
H
OH
OH
-glucose
OH
H OH
H
O
H OH
HO
H
HO
H
OH
H
H
O
O
H
HO
H
1,4-glycosidic linkage
Maltose
H
OH
OH
OH
HOH 2C
5
H
OH
H
2
Rotate
CH 2OH
HO
H
HOH 2C
O
180o
2
O
H
OH
HO
H
CH 2OH
HO
-fructose
5
H
H OH
H
HOH 2C 1
H
+
HO
1
H
H
OH
HO
OH
H
H
2
O
HO
O
CH 2OH
H
HO
OH
-fructose
-glucose
H OH
H
O
H
HOH 2C
HO
1
HO
H
H
O
2
H
OH
OH
O
H
1,2-glycosidic linkage
Sucrose
CH 2OH
HO
H
Testing for reducing sugars
 Reducing sugars - sugars that contain free aldehyde group
 Give red ppt of Cu2O when treated with Fehling’s
solution
Complex ion of Cu2+ + RCHO
Deep blue
Cu2O(s)
Red
• All monosaccharides are reducing sugars
H OH
H
1
+
O
6
C
H
5
O
HO
H
C
OH
1
HO
H
HO
C
H
H
H
H
C
5
C
OH
~36%
H OH
..
OH
(Fischer projection)
~0.02%
OH
-glucose
OH
CH 2OH
H
6
5
HO
H
O
1
HO
H
H
OH
-glucose
H
~64%
OH
H
H
OH
OH
C
C
O
C
OH
HO
C
H
HO
C
H
H
C
OH
H
C
H
C
OH
H
C
CH 2OH
O
C
C
H
H
H
C
OH
HO
C
H
OH
H
C
OH
OH
H
C
OH
CH 2OH
Fructose
CH 2OH
Glucose
Fructose undergoes transformation to give glucose
 Fructose is a reducing sugar
H OH
H
O
Maltose
H OH
HO
H
HO
H
OH
H
O
O
H
H
HO
H
OH
H
OH
The right ring is able
to open to give a
free aldehyde group
which can be oxidized
H OH
H
O
H OH
HO
H
HO
H
H
OH
5
H
OH
O
1
HO
H
H
OH
O
H
 A reducing sugar
H OH
H
HOH 2C 1
H
+
HO
1
H
H
OH
HO
OH
H
H
2
O
HO
O
CH 2OH
H
HO
OH
-fructose
-glucose
H OH
Both rings are locked
H
 non-reducing sugar
O
H
HOH 2C
HO
1
HO
H
H
O
2
H
OH
OH
O
H
1,2-glycosidic linkage
Sucrose
CH 2OH
HO
H
Polysaccharides
nC6H12O6
Starch
-glucose
nC6H12O6
-glucose
Cellulose
Amylose
Starch
Amylopectin
Amylose - consists of unbranched chains of -glucose
units joined by -1,4 linkages
Amylopectin - consists of highly branched chains of
-glucose units linked by -1,4 linkages
Amylose
H OH
H O
H OH
O
HO
H
H
H
OH
H O
O
HO
H
H
H OH
H
OH
H O
O
HO
H
H
HHO
H
H O
OH
H OH
H
O
HO
H
H
H O
OH O
HO
H
H
1,4 glycosidic linkages
OH
H
O
H OH
H O
H OH
O
H O
O
HO
H
H
OH
H
O
HO
H
HO
H OH
H
H
H O
H
OH
OH
Amylopectin
H
HO
H OH
H
H
O
H O
H
H
OH
H OH
O
H
HO
H
H
OH
OH 1
H
H O
HO
H OH
H O
O
H
H
1,6-glycosidic
linkages
H OH
H
O
HO
H O
O
HO
H
H
OH
O
6
H O
1
OH
H
H
H
O
H
H
O
HO
6
H O
H
H
H
OH
OH
Cellulose : -
•
consists of unbranched chains
of -glucose units joined by
1,4-glycosidic linkages
•
the structural component of
cell walls of plant
The 2nd unit
is flipped over
H OH
H
H O
4
O
HO
HO
1
H
H
O
4
OH
H
H OH
HO
H
H
H
OH 1
H O
4
O
H O
1
HO
H
OH
H
H
1,4 - glycosidic linkages
O
Hydrolysis of Sucrose
C11H22O11 + H2O
sucrose
[]D = +66. 5o
Dextrorotatory(+)
H+ or
invertase
C6H12O6 + C6H12O6
glucose
fructose
[]D = +52.7o
[]D = -92.4o
Laevorotatory (-)
The reaction mixture undergoes an inversion in
optical activity (from + to -)
Hydrolysis of Starch
2(C6H10O5)n + nH2O
amylase
Maltose
Starch
C12H22O11 + H2O
nC12H22O11
maltase
2C6H12O6
Glucose
(C6H10O5)n + nH2O
Starch
H+
nC6H12O6
Glucose