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1.2 CARBOHYDRATES

1.4 PROTEINS

1.3 LIPIDS

1.5 NUCLEIC ACIDS

1.1 WATER

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1.2 CARBOHYDRATES

1.2 Carbohydrates (1 1/2 hour)Objectives :

• Describe various forms and classes of carbohydrates such as monosaccharides, disaccharides & polysaccharides.

• Describe the formation and breakdown of maltose.

• Describe the structures and functions of starch, glycogen & cellulose.

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CARBOHYDRATE

MONOSACCHARIDES

Triose (3C)

Pentose (5C)

Ribose Deoxyribose

Hexose (6C)

GlucoseGalactoseFructose

DISACCHARIDES

MaltoseSucrose Lactose

POLYSACCHARIDES

StarchGlycogenCellulose

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CARBOHYDRATES

MONOSACCHARIDES

Single / Simple sugar

DISACCHARIDES

Double sugars; consist of 2 monosaccharides

POLYSACCHARIDES

Complex sugars; polymers of many

sugars

3 main classes

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• all are composed of carbon (C), hydrogen (H) & oxygen (O) atoms ;

• usually in the proportion 1:2:1 respectively

CARBOHYDRATES

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MONOSACCHARIDES • characteristics:

1. simple sugars: - cannot be broken down into

smaller molecules by hydrolysis

2. sweet-tasting3. soluble in water

CARBOHYDRATES

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MONOSACCHARIDES

• ..characteristics:

4. can be crystallized5. reducing agents:

- it has an open chain with an aldehyde or a ketone group.

6. can be the monomers for disaccharides & polysaccharides

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• general formula: ( CH2O )n

n = number of C atoms in the molecule, ( n = 3, 4, 5, 6, 7 )

eg: glucose ~ C6H12O6

~ most names for sugars end with -ose

MONOSACCHARIDES

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CARBOHYDRATES

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MONOSACCHARIDESSTRUCTURE

• straight-chain form, ring form in aqueous

• a sugar has;

i. a carbonyl group ( C = O )

ii. many hydroxyl groups ( -OH )

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can be classified as;

1. based on the type of functional group ( aldehyde or ketone )

2. by the number of carbon atoms in the backbone

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CLASSIFICATION : FUNCTIONAL GROUPif the carbonyl group ( C=O ); at one end of the

molecule ( C1 atom )

aldehyde group = the sugar is an aldose

if in the middle of the molecule ( C2 atom )

ketone group= the sugar is ketose

Aldehyde

Ketone

also classified by the number of carbon atoms in the backbone;

Triose sugar ( 3C sugars ): ~ contains 3 carbon atoms~ C3H6O3 ~ eg: glyceraldehyde

Pentose sugar ( 5C sugars ): ~ contains 5 carbon atoms~ C5H10O5 ~ eg: ribose, deoxyribose

Hexose sugar ( 6C sugars ): ~ contains 6 carbon atoms ~ C6H12O6 ~ eg: glucose, galactose & fructose

CLASSIFICATION : NUMBER OF CARBONS

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CLASSIFICATION : FUNCTIONAL GROUP & NUMBER OF CARBONS

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CARBOHYDRATE

MONOSACCHARIDES

Triose (3C

)

Pentose

(5C)Ri

bose

Deoxyribose

Hexose (6C

)Glucose

GalactoseFructose

DISACCHARIDES POLYSACCHARIDES

Triose sugar: Glyceraldehyde

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Pentose sugar

Hexose sugar : Glucose

Structure of Glucose

Aldohexose

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Two ring structure of glucose• - glucose and - glucose• difference : whether the hydroxyl

group (-OH) attached to the number 1 carbon is fixed above ( - glucose) orbelow ( - glucose )

Linear structure

Ring structure

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• both are isomers (different compounds with the same

molecular formula C6H12O6 )

..Two ring structure of glucose

1

1

Hexose sugar : Glucose

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CARBOHYDRATE

MONOSACCHARIDES DISACCHARIDESMaltos

eSucros

e Lactos

e

POLYSACCHARIDES

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DISACCHARIDES

• sweet & water soluble• a double sugar molecule

( consists of 2 monosaccharides ) • Can be crystallized

CARBOHYDRATES

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Glycosidic bondof carbohydrates;

• bond between 2 monosaccharides;• formation by a condensation reaction;

» removal of water molecule

• breakage by a hydrolysis reaction;» addition of water molecule

CARBOHYDRATES

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DISACCHARIDES

Maltose ( malt sugar ) = α-glucose + α-glucose~ as respiratory substrate~ reducing sugar

Sucrose ( cane sugar ) = α-glucose + fructose~ main form that is transported in plant~ non-reducing sugar

Lactose ( milk sugar ) = β-glucose + galactose~ source for energy~ reducing sugar

CARBOHYDRATES

Reducing agent:depend on free functional

group ( aldehyde & ketone )

at sugar structure

Sucrose:~ non-reducing sugar

Maltose & Lactose~ reducing sugar

CARBOHYDRATES

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MALTOSE = α-glucose + α-glucose

condensation

hydrolysis

This reducing group is still free

α-1,4

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SUCROSE =α-glucose + fructose

condensationhydrolysis

A non-reducing sugar because the aldehyde group of glucose is linked to the ketone group of fructose

α-1,2

Disaccharides: LACTOSE

O

1

23

4

5

6

OHH

CH2OH

O HHHO

H

H OH

H

galactose β - glucose +

O

1

23

4

5

6

OHOH H

CH2OH

OHHH

H

H OH

Disaccharides: LACTOSE

O

1

23

4

5

6

OHH

CH2OH

OHHO

H

H OH

H

O

1

23

4

5

6

OH H

CH2OH

OHHH

H

H OH

( β- 1,4 glycosidic bond )

H2O

Lactose

LACTOSE = galactose + glucose

Raven pg 54, fig 3.23

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CARBOHYDRATE

MONOSACCHARIDES DISACCHARIDES POLYSACCHARID

ES

StarchGlycog

enCellulo

se

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POLYSACCHARIDES

• complex macromolecules• polymers formed when many

hundreds of monosaccharides joined by glycosidic bonds ( through condensation )

• breakdown by hydrolysis

CARBOHYDRATES

POLYSACCHARIDES

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POLYSACCHARIDES• The chains formed may be:

• variable in length

• branched or unbranched

• folded – ideal for energy storage

• straight or coiled

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POLYSACCHARIDES• characteristic of polysaccharides:

• large• not sweet • insoluble in water• Cannot be crystallized

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POLYSACCHARIDESexamples: • STARCH (plant food storage)

• GLYCOGEN (animal food storage)

• CELLULOSE (components of plant cell wall)

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POLYSACCHARIDESStarch• used for energy storage in plants

• a polymer consists of α-glucose subunits

• occurs in 2 forms:1. Amylose2. Amylopectin

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Starch

: stored as granules within plastids in leaves, potato tubers, cereals & rice

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CARBOHYDRATESStarchAmylose:

• subunit: α-glucose• unbranched helical chains,

• only one type of linkage: α-1,4 glycosidic bond

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Amylose

Hydrogen bond

Monomers linked by α-1,4 glycosidic bond

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..Amylose

• amylose chain coils into helix held by hydrogen bonds formed between hydroxyl ( -OH ) groups

~ a more compact shape is formed

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Hydrogen bond

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CARBOHYDRATESStarchAmylopectin:

• subunit: α-glucose• branched chains every 30 units,

• have 2 types of linkages:

α-1,4 glycosidic bond & α-1,6 glycosidic bond

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α- 1,6 glycosidic

bond

α-1,4 glycosidic bonds

Amylopectin

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CARBOHYDRATES

Glycogen• carbohydrate energy stored in animals• found in liver & muscle tissue• structure is similar to that of

amylopectin but more extensively branched

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Glycogen

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α- 1,6 glycosidic bond

α- 1,4 glycosidic bond

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Cellulose

Monomers linked by β-1,4 glycosidic bond

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..Cellulose

Cellulose• consists of β- glucose monomers

linked (upside down to each other) by β- 1,4 glycosidic bonds

CARBOHYDRATES

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..Cellulose

Cellulose• long chain ( unbranched chains )

• many H bonds are formed between the hydroxyl groups on adjacent chains ( parallel to one another )

CARBOHYDRATES

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Cellulose

OHOHOH

OHOHOH

OH

OH

Hydrogen bond

CARBOHYDRATES

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..Cellulose

• many parallel cellulose chains are held together forming microfibrils ( strong building cables ) • making the cell wall a very stable structure ( strength & rigid )

CARBOHYDRATES

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fibrilmicrofibril

Cellulose fibrils in plant cell wall (TEM)

cellulose chains

polymers of beta glucose

cell wall

PLANT CELLS

glucose monomer

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Hydrogen bond

Cellulose

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CARBOHYDRATESFUNCTIONS:• Energy source

substrate of cell respiration (eg. Glucose)• Energy storage (many C-H bonds)

in animal: glycogen in plants: starch

• Structural component of cell membranes & cell walls cell walls: cellulose plasma membrane: oligosaccharides

SEMESTER 1SESSION 2001 / 2002

Question

• What is carbohydrate?

By providing suitable examples, explain briefly the four roles of carbohydrate in plants.

[6 marks]

SESSION 2001 / 2002

Question

• Given an example of a disaccharide and polysaccharide. List the differences between disaccharide and polysaccharide.

[8 marks]

References :

• Campbell, 8th edition• Solomon, 9th edition

Next Subtopic….• 1.3 Lipids

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1.2 CARBOHYDRATES

1.4 PROTEINS

1.3 LIPIDS

1.5 NUCLEIC ACIDS

1.1 WATER