CARBOHYDRAT

E CHEMISTRY

Dr.Almoeiz Yousif

MS.c.,Ph.D.,MEE

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Carbohydrates • Carbo(C)……Hydrate (hydrates of carbon) • Most have general formula CnH2nOn

I (CH2O)n or H - C - OH

I

Carbohydrate Definition

polyhydroxyaldehyde or polyhydroxyketone, or a substance that can be hydrolyzed to form these compounds

I (CH2O)n or H - C - OH

I

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Functions of Carbohydrates

• Structural role

• Energy source

Classification of Carbohydrates

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Disaccharides - 2 monosaccharides

covalently linked.

Polysaccharides - more than

10 monosaccharide units

covalently linked.

Oligosaccharides – 3 to 10

monosaccharides

covalently linked.

Monosaccharides - simple sugars

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Monosaccharides A monosaccharide is a carbohydrate

that cannot be hydrolyzed to a simpler carbohydrate (simple sugar)

• biologically important ones are:

• Glucose: most common sugar,

also blood sugar

• Fructose : fruit sugar

• Galactose: sugar found in milk

Properties of Monosaccharides

•Simplest of carbohydrates

•Sweet-tasting

•Dissolve in water

•Straight chain or ring structure

•Reducing sugars

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Monosaccharide Classification •1- On the basis of the numbers of carbon atoms •2- On the basis of the functional group.

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1. According to number of carbons

• 3 carbons triose

• 4 tetrose

• 5 pentose (ribose)

• 6 hexose (glucose,fructose galactose)

• 7 heptose

• 8 octose

• 9 nonose

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2.According to functional group

Aldoses have an aldehyde group at one end.

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Ketoses have a keto group,

usually at C2.

C

C OHH

C HHO

C OHH

C OHH

CH2OH

D-glucose

OH

C HHO

C OHH

C OHH

CH2OH

CH2OH

C O

D-fructose

ISOMERS: same chemical formulae

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C6H12O6

ISOMERS OF MONOSACCHARIDES

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1) D- and L- isomers

= mirror images (enantiomers)

nature important: D-monosaccharides

2)Aldoses and Ketoses

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C

C OHH

C HHO

C OHH

C OHH

CH2OH

D-glucose

OH

C HHO

C OHH

C OHH

CH2OH

CH2OH

C O

D-fructose

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3) pyranoses and furanoses Sugars Prefer To Be Cyclic in solutions

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99% of Glucose in solution

is found in pyranose form

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4) and anomers

only cyclic molecules

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-D-Glc

* OH orientation of anomeric carbon is the basis of this classification.

β anomer : Same side with the side chain( the last carbon atom)

α anomer : opposite side with the side chain

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5) epimers

EPIMERS:differ in conformation around ONE carbon

Man = 2-epimer of Glc

Gal = 4-epimer of Glc

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Gal is found in lactose (milk sugar)

Galaltose and Mannose are epimers of glucose

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Joining of

monosaccharaides

• Monosaccharaides can be joined to form

disaccharides, oligosaccharides, and

polysaccharides. Important disaccharides include

lactose (galactose + glucose), sucrose (glucose +

fructose), and maltose (glucose + glucose).

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• Important polysaccharides include branched

glycogen (from animal sources) and starch (plant

sources) and unbranched cellulose (plant sources);

each is a polymer of glucose.

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Glycosidic bond

• a glycosidic bond or glycosidic linkage is a type of

covalent bond that joins a carbohydrate (sugar)

molecule to another .

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Naming glycosidic bonds:

• Glycosidic bonds between sugars are named

according to the numbers of the connected

carbons, and also with regard to the position of the

anomeric hydroxyl group of the sugar involved in the

bond. If this anomeric hydroxyl is in the α

configuration, the linkage is an α-bond.

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• If it is in the β configuration, the linkage is a β-bond.

Lactose, for example, is synthesized by forming a

glycosidic bond between carbon 1 of β-galactose

and carbon 4 of glucose. The linkage is, therefore, a

β(1→4) glycosidic bond

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DISACCHARIDES

• Sucrose

• LActose

• MaltosE

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Disaccharide

• Two joined monosaccharaides are called a disaccharide

and these are the simplest polysaccharides. Examples

include sucrose and lactose. They are composed of two

monosaccharide units bound together by a covalent bond

known as a glycosidic linkage formed via a dehydration

reaction, resulting in the loss of a hydrogen atom from

one monosaccharide and a hydroxyl group from the other.

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Disaccharides

• Two simple sugars joined together.

Maltose (malt sugar) = glucose + glucose

Sucrose (table sugar) = glucose + fructose

Lactose (milk sugar) = glucose + galactose

Two monosaccharaides can join with a glycosidic linkage to form a disaccharide.

Maltose

•Maltose is formed by joining two glucose molecules.

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Sucrose

• is formed by joining glucose and fructose.

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Lactose

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Lactose Intolerance

• Symptoms

• Bloating, abdominal discomfort, and

diarrhea

• Causes

• Lactase deficiency

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Oligosaccharides

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Oligosaccharides

• 3-10 monosaccharaides linked together

e.g.

•Maltotriose (3 glucose units

• Dextrin (6-8 glucose units

Polysaccharides

Polysaccharides

• Polysaccharides: more than 10 monosaccharide

units linked together.

• polysaccharides are insoluble in water.

• Polysaccharides can be polymers of hexose or

pentose sugars.

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Polysaccharides • Examples: Polymers of glucose Starch: Storage form of glucose in plants.

Cellulose: Structural element of plants. Glycogen: Storage form of glucose in animals.

Chitin: Structural element in the exoskeletons of insects.

GLYCOGEN

GLUCOSE IS STORED AS GLYCOGEN IN

LARGE AMOUNTS IN BOTH THE LIVER AND

SKELETAL MUSCLES

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Structural Polysaccharides

• Chitin is the major element in the exoskeleton of insects and crustacea where it affords protection and support.

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