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 substa

nces 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

H2N CH C

H

OH

O

• Most proteins are formed from some twenty common

amino acids, linked up by peptide bonds

H N

H

C

H

C

O

OH

R

+ H N

H

C

H

C

O

OH

R'

Peptide linkage

H N

H

C

H

C

O

N

R

C C

O

OH

R'H

H

+ H2O

• 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) C6H12O6(s) + 6O2(g)

light

chlorophyll

Classification of Carbohydrates

• Monosaccharides - (CH2O)n where n>2

E.g. C6H12O6 Hexose (most important)

C5H10O5 Pentose

Aldohexose

Glucose

Ketohexose

Fructose

C

C

OH

OHH

C HHO

C OHH

C OHH

CH2OH

1CH2OH

C O

C HHO

C OHH

C OHH

CH2OH

2

• Disaccharides

• Polysaccharides

- C12H22O11 E.g. Maltose, Sucrose

- (C6H10O5)n where n is a very large number

E.g. Starch, Cellulose

Open chain and cyclic structures of glucose and fructose

+

..

C

C

OH

OHH

C HHO

C OHH

C OHH

CH2OH

(Fischer projection)

O

H

HO

H

HO

H

OH

OHHH

OH

O

H

HO

H

HO

H

H

OHHOH

OH

1

56

1

56

-glucose

-glucose

5

1

• 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).

CH2OH

C O

C HHO

C OHH

C OHH

CH2OH

Fructose

..5

+2

OH

CH2OH

H

HOH2C

HO H

H OH

O

6

11

25

6

O

H

HO

OH

H

OH

OH

HH

H

CH2OH..

-furanose

-pyranose

1

2

6

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

2C6H12O6

CondensationC12H22O11 + H2Ohydrolysis

Glucose + Glucose Maltose + water

Glucose + Fructose Sucrose + water

O

H

HO

H

HO

H

OH

OHHH

OH

O

H

HO

H

HO

H

OH

OHHH

OH

+1

4

O

H

H

HO

H

OH

OHHH

OHO

H

HO

H

HO

H

OHHH

OH

O

1,4-glycosidic linkage

Maltose

-glucose-glucose

CH2OH

H

HO

HOH2C

HO H

H OH

O

CH2OH

OH

H

HOH2C

HO H

H OH

O

25 2 5Rotate 180o

-fructose

O

H

HO

H

HO

H

OH

OHHH

OH

-glucose

+CH2OH

H

HO

HOH2C

HO H

H OH

O

-fructose

1

1

2

CH2OH

HHOH2C

HO H

H OH

O

O

H

HO

H

HO

H

OHHH

OH

O

1 2

1,2-glycosidic linkage

Sucrose

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 Cu2O(s)

Deep blue Red

C

C

OH

OHH

C HHO

C OHH

C OHH

CH2OH

• All monosaccharides are reducing sugars

+

..

(Fischer projection)

O

H

HO

H

HO

H

OH

OHHH

OH

O

H

HO

H

HO

H

H

OHHOH

OH

1

56

1

56

-glucose

-glucose

5

1

~0.02%~64%

~36%

Fructose

C

C O

C HHO

C OHH

C OHH

CH2OH

H

H OH C

C OH

C HHO

C OHH

C OHH

CH2OH

H OHC

C OH

C HHO

C OHH

C OHH

CH2OH

H O

H

Glucose

Fructose undergoes transformation to give glucose

Fructose is a reducing sugar

O

H

H

HO

H

OH

OHHH

OHO

H

HO

H

HO

H

OHHH

OH

O

Maltose

OH

H

H

HO

H

O

OHH

OHO

H

HO

H

HO

H

OHHH

OH

OH1

5

The right ring is able to open to give a free aldehyde group which can be oxidized

A reducing sugar

O

H

HO

H

HO

H

OH

OHHH

OH

-glucose

+CH2OH

H

HO

HOH2C

HO H

H OH

O

-fructose

1

1

2

CH2OH

HHOH2C

HO H

H OH

O

O

H

HO

H

HO

H

OHHH

OH

O

1 2

1,2-glycosidic linkage

Sucrose

Both rings are locked

non-reducing sugar

Polysaccharides

nC6H12O6

-glucose

Starch

nC6H12O6

-glucose

Cellulose

StarchAmylose

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

O

H

O

H

HO

H

OOHHH

OH

O

H

H

HO

H

OOHH

H

OH

O

H

H

HO

H

OOHH

H

OH

O

H

H

HO

H

OOHH

H

HO

O

H

H

HO

H

OOHH H

OH

Amylose

1,4 glycosidic linkages

O

H

O

H

HO

H

OHHH

OH

O

H

O

H

HO

H

OHHH

OH

O

H

O

H

HO

H

OHHH

OH

O

H

O

H

HO

H

OHHH

OH

O

H

H

HO

H

OHHH

OH

O

H

O

H

HO

H

OHHH

O

O

H

O

H

HO

H

OHHH

OH

O

H

O

H

HO

H

OH

OHHH

O

O

H

O

H

HO

H

OHHH

OH

O

1

6

1

6

Amylopectin

1,6-glycosidic linkages

Cellulose : -

• consists of unbranched chains of -glucose units joined by 1,4-glycosidic linkages

• the structural component of cell walls of plant

O

H

O

H

HO

H

H

OHHO

OH

OH

H

HO

H

H

OHH

O

HO

O

H

H

HO

H

H

OHH

O

OH

1 4

4 1 41

1,4 - glycosidic linkages

The 2nd unit is flipped over

Hydrolysis of Sucrose

C11H22O11 + H2O C6H12O6 + C6H12O6

H+ or

invertaseglucose fructosesucrose

[]D = +66. 5o[]D = +52.7o []D = -92.4o

The reaction mixture undergoes an inversion in optical activity (from + to -)

Laevorotatory (-)Dextrorotatory(+)

maltaseC12H22O11 + H2O 2C6H12O6

Glucose

2(C6H10O5)n + nH2Oamylase

nC12H22O11

MaltoseStarch

(C6H10O5)n + nH2O H+

nC6H12O6

Starch Glucose

Hydrolysis of Starch