2

Medical Biochemistry and Molecular

Biology

CARBOHYDRATE CHEMISTRY

ByAyman Elsamanoudy

Objectives (ILOs)I. to study the definition, classification of

carbohydrates

II. to know the biological importances of

carbohydrates.

III. to know the important body structure formed

by carbohydrate molecules and study its

functions .

IV. to understand how any disorder in

carbohydrates structure or function leads to

disease.3

Carbohydrates are :

Organic compounds composed of C.H.O.

Contain more than hydroxyl group.

Contain active carbonyl group ;aldehyde at C1 or

ketone group at C2.

Generally but not always the hydrogen and oxygen

in carbohydrates are present in the proportion of

2H and one oxygen atoms as in water.

4

Definition:

Carbohydrates are polyhydroxy aldehydes or

polyhydroxy ketones and compound giving them

on hydrolysis

5

Function of carbohydrates1. They serve as energy stores and fuels.

2. They enter in the structure of cell membranes.

3. Pentose sugars (ribose and deoxyribose) enter in the

structure of nucleic acids.

4. Carbohydrates enter in the structure of glycoproteins and

glycolipids.

5. Carbohydrates play important roles in recognition

between cell types or recognition of cellular structures by

other molecules.

NB: Recognition events are important in normal cell

growth, fertilization and transformation of cells.

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Classification Monosaccharides Disaccharides Oligosaccharides Polyosaccharides

Diff The simplest

carbohydrates.

They contain only

one sugar unit .

-cannot be

hydrolysed into

simpler units

2 monsacch.

Units linked to

each other by

glycosidic bond

3-10 monsacch. Units linked to

each other by glycosidic bond

More than 10

monsacch. Units

linked to each other

by glycosidic bond

Ex. Glucose …. Sucrose &

Lactose……

1-Maltotriose = 3 glucose units

2-Raffinose

(tri-saccharide=

glucose+glactose+fructose)

Starch …….

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Monosaccharides

Are carbohydrates which, contain only one sugar

unit and cannot be hydrolyzed into smaller units

( the simplest form of carbohydrates).

They are further classified according to:

1. Number of carbon atoms contain.

2. Whether they are aldehydes or ketones.

3. According to number of carbon atom as well as

adlehydes and ketones.

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9

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Number of Carbons

(Generic

monosaccharide

name)

Aldose Functional

Group

Ketone Functional

Group

3

)oseTri(osetriAldo

osetriKeto

uloseTri

4

)oseTetr(osetetrAldo

osetetrKeto

Tetrulose

5

ose)Pent(osepentAldo

osepentKeto

Pentulose

6

)oseHex(osehexAldo

osehexKeto

Hexulose

Aldoses

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Ketoses

Structural formula of monosaccharidesA) Straight (open) chain formula :

B) Cyclic structural formula .

1-Fischer projection form:

2-Haworth form

1-simple chain

formula

(Acyclic form)

2- Cyclic structure formula:

In the solution, the sugar which has an aldehyde group undergoes the

following:Hydration of aldehyd group to form aldenol group>>>>>then

condensation between OH group of aldenol and OH of C4 or C5 to form ring

structure.

a-Fischer projection formula:the

aldhyde or ketone group react

with one OH group to form

hemiacetal or hemiketal

b- Haworth formula:

Which may be : pyranose or

furanose

Steps of the cyclic form construction:

1. Hydration of aldehyde or keto group toform aldenol or ketonol group producingaldenol or ketonol form of monosacharide.

CHO

C OHH

C HHO

C OHH

C OHH

CH2OH

+ H2O

C

C OHH

C HHO

C OHH

C OHH

CH2OH

H

OHHO

+ H2O

C

C OHH

C HHO

CH

C OHH

CH2OH

H

OH

C

C OHH

C HHO

C OHH

CH

CH2OH

HOH

O

(or) -D-Glucofuranose

HO

HO

O

Furan ring

O

Pyran ring

OR

(or) -D-Glucopyranose

D-Glucose D-Glucose aldenol,

unstable

O

CH2OH

C = O

C HHO

C OHH

C OHH

CH2OH

+ H2O

CH2OH

C OHHO

C HHO

C OHH

C OHH

CH2OH

+ H2O

CH2OH

C OH

C HHO

C OHH

CH

CH2OH

O

CH2OH

C OH

C HHO

C OHH

C OHH

H2C O

(or) -D-Fructofuranose

O

Furan ring

O

Pyran ring

OR

(or) -D-Fructopyranose

D-Fructose D-Fructose ketonol,

unstable

HO

HO

Then

2- The OH group from the aldenol group condenses

with the OH :

on C4 or C5 of the aldo-sugar to forms a ring or

hemi-acetal structure with the liberation of H2O

again.

Keto-sugar condenses only with C5 or with C6

giving Hemiketal form .

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The aldehyde or

ketone group can react

with a hydroxyl group

to form a covalent

bond.

An aldehyde reacts

with a hydroxyl group

creates a hemiacetal.

A ketone reacts with a

hydroxyl group to

form a hemiketal.

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Haworth's formula:

Because Fisher’s formula could not explain some ofthe chemical and physical characteristics of sugars,Haworth put forth his formula.

. C and O atoms of the ring are drawn in the plane ofthe page.

H and OH or other side groups are written onperpendicular plane.

All groups located on the left side of fisher’s arewritten upwards. All groups located on the rightside of fisher’s are written downwards Except inLast C in the ring .

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6 membered oxy ring 5 membered oxy ring

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MCQs

The aldose sugar is

(A) Glyceraldhyde

(B) Ribulose

(C) Erythrulose

(D) Dihydoxyacetone

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A triose sugar is

(A) Glycerose

(B) Ribose

(C) Erythrose

(D) Fructose

A pentose sugar is

(A) Dihydroxyacetone

(B) Ribulose

(C) Erythrose

(D) Glucose

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. Ribulose is a these

(A) Ketotetrose

(B) Aldotetrose

(C) Ketopentose

(D) Aldopentose

A carbohydrate, commonly known as dextrose is

(A) Dextrin

(B) D-Fructose

(C) D-Glucose

(D) Glycogen

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Which of the following is a keto sugar

A) Galactose

B) Fructose

C) Glucose

D) Mannose

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Glycosidic bond is absent in

A) Disacharide

B) oligosacharide

C) Monosacharide

D) Polysacharide

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Hydration of glucose leads to formation of

A) Stable alcohol

B) Unstable aldenol form of glucose

C) Direct cyclization of glucose

D) No effect

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Fructofuranose is

A) Straight chain formula of

fructose

B) Fischer projection formula of

fructose

C) Ketenol form of fructose

D) 6 membered oxy ring of

fructose

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The predominant form of glucose in

solution is

(A) Acyclic form

(B) Hydrated acyclic form

(C) Glucofuranose

(D) Glucopyranose

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Asymmetric carbon atom (chiral carbon)

Def: It is a carbon atom which is attached to 4

different group or atoms e.g. middle carbon of

glyceraldhyde.

Any substance having asymmetric carbon atom

posses the following:

I. Show optical activity.

II. Show optical isomerism (stereoisomerism)

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Optical activity

DIFF:It is the ability of the compound to rotate

plane polarized light either towards the right or

towards the left.

Plane polarized light: is an ordinary light after

passing through special type of prism called Nicols

prism (CaCO3), the light emerging form such

prism vibrate in a single plain.

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Types of optically active sugar solutions

A. If the compound rotate plane polarized light to the right, it

is called >>>>dextrorotatory, d or (+).

Example: Glucose is dextrorotatory so it is sometimes called

dextrose.

B. If the compound rotate plane polarized light to the left, it

is called>>>>>. levorotatory, l or (-).

Example: Fructose is levorotatory so it is sometimes called

levulose.

NB :All monosaccharides are optically active, except

dihydroxy acetone, this is due to the presence of

asymmetric carbon atoms.36

Measurement of optical activity

By : Polrimeter or Polriscope

Composition :

1- source of light (Na light).

2-A Nicol prism(polarizer):it converts ordinary

scattered light into PPL.

3- A glass tube in which the exmined solution will

be done.

4- Analyzer which determine the angel of rotation.

5- Detector

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Specific rotation

It is the angle of rotation specific for each

optically active substance when the

concentration of substance is 100 g/dl and the

length of measuring tube is 10 cm using Na

light at 20 Ċ.

Examples :

The specific rotation :

1. for glucose is + 52.5 &

2. for fructose is - 91.

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Factors affecting specific rotation

1. Type of light.

2. Length of the tube.

3. Nature and concentration of substance.

4. Temperature.

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Optical isomerism

Def :Compounds having the same structural

formulae (same chemical group) but differ in the

way these groups are attached in space around only

one of its asymmetric carbon atom.

The number of optical isomers = 2n where n =

number of asymmetric carbon atoms in a molecule.

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Types of isomerism of monosacharides:

1-Enantiomers: (D & L configuration).

2-Anomers or α and β isomer.

3-Epimers.

4-Aldose and ketose isomers .

5-Pyranose and furanose isomers

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Enantiomers: (D & L) isomers

Concept: Two isomers which are mirror images .

Reffered to : prelast carbon which is the last asymetric

C atom .

Types of enantiomers :

1- D form: OH attached to the right of prelast C.

2-L form: OH attached to the left of prelast C

Description :They differ in all carbons (mirror image)

but D & L configuration is according to H – OH

orientation in the pre-last C.

NB: The great majority of the sugars in humans are D-

sugars

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Anomers :α and β isomer

Concept:These are isomers that differ in position of OH

group at the anomeric carbon atom.

Reffered to: anomeric C atom

Def of annomeric C atom: is the asymmetric carbon atom

obtained from active sugar group in the cyclic structure .

Position of anomeric C:C1 in aldose and C2 of ketose).

Types of anomers :

1- α sugar : OH group attached to the anomeric carbon is

on the right side.

2- β sugar. OH group attached to the anomeric carbon is

on the left side.49

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Epimers Concept :If two monosaccharides differ in

configuration around only one asymtetric carbon

atom other than anomeric C& the prelist C atom

,((the epimeric carbon))>>>> they are defined as

epimers of each other.

Referred to: epimeric carbon .

Def of epimeric carbon : asymtetric carbon atom

other than anoneric& the prelist C atoms.

Examples : usually erpimers are described in pairs :

. Glucose & galactose are C4 epimer. .

Glucose & mannose are C2 epimer

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Aldose and ketose isomers

Concept :Two isomers have the same molecular

formula but differ in aldhyde group or ketone group

Example :. glucose --- fructose

ribose --- ribulose.

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Pyranose and furanose isomers

Glucose can be present in glucopyranose and as

glucofuranose both are isomers.

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MCQs

The number of isomers of glucose is

(A) 2

(B) 4

(C) 8

(D) 16

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Isomers differing as a result of

variations in configuration of the —OH

and —H on carbon atoms 2, 3 or 4 of

glucose are known as

(A) Epimers

(B) Anomers

(C) Optical isomers

(D) Steroisomers

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The most important epimer of glucose is

(A) Galactose

(B) Fructose

(C) Arabinose

(D) Xylose

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-D-glucose and -D-glucose are

(A) Stereoisomers

(B) Epimers

(C) Anomers

(D) Keto-aldo pairs

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Which of the following is an epimeric pair?

(A) Glucose and fructose

(B) Glucose and galactose

(C) Galactose and mannose

(D) Lactose and maltose

D-Glucose and D-glucose are related by

(A) Epimers

(B) Anomers

(C) aldose ketose isomers

(D) pyranose-furanose isomers

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Sugar Derivatives

They include:

I. Sugar Acids.

II. Sugar Alcohols.

III. Deoxysugars.

IV.Amino Sugars.

V. Amino sugar acids.

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Sugar Acid. Def: They are the oxidation products of monosaccharides

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Aldonic acids: Uronic acids: Aldaric acids:

deff Oxidation of carbonyl

group to carboxylic

group yields aldonic

acid.

Oxidation of the last

carbon yields uronic

acids

They are dicarboxylic

resulting from oxidation of

both carbonyl carbon and

last hydroxyl carbon,

Oxidation of

glucose gives

Gluconic acid Glucuronic acid

L iduronic acid

Glucaric acid

1.Aldonic

CHO

C OHH

C HHO

C OHH

C OHH

CH2OH

COOH

C OHH

C HHO

C OHH

C OHH

CH2OH

bromine water, O2

D-Gluconic acidD-Glucose

2-Uronic

CHO

C OHH

C HHO

C OHH

C OHH

CH2OH

CHO

C OHH

C HHO

C OHH

C OHH

COOH

Dil. Nitric acid

D-Glucuronic acidD-Glucose

H2O2

3-Aldaric

CHO

C OHH

C HHO

C OHH

C OHH

CH2OH

COOH

C OHH

C HHO

C OHH

C OHH

COOH

Conc. Nitric acid

D-Glucaric acidD-Glucose

O2

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COOH

C

C

C

C

H OH

HO H

H OH

D-gluconic acid D-glucuronic acid

CH2OH

OHH

CHO

C

C

C

C

H OH

HO H

H OH

COOH

OHH

Imortance of Iduronic acid :

glycosaminoglycans formation

(mucopolysaccharides)

Imortance of Glucuronic acid :

1. Detoxication reactions.

2. Formation of

glycosaminoglycans

(mucopolysaccharides).

3. Metabolism of bilirubin.

4. Excretion of steroids.72

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L-ascorbic acid (vitamin C)

It is a 6-carbon sugar acid.

It is water soluble and optically active.

Humans are unable to synthesize it and hence must

be supplied in the diet.

It has 2 forms:

reduced form ( ascorbic acid )

oxidized form ( dehydroascorbic acid )

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Ascorbic acid

(reduced form)

dehydrAscorbic acid

(oxidized form)

2-Sugar alcohols (Alditols)

Diff: It is the product of reduction of the active

carbonyl group .

Concept: Aldoses and Ketoses may be reduced at the

carbonyl carbon to the corresponding polyhydroxy

alcohols (sugar alcohols).

Examples :

D-glucose D-sorbitol.

D-mannose D-mannitol.

D-fructose D-sorbitol and D-mannitol.

D-galactose D-galacticol.

D-ribose D-ribitol76

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CHO

C

C OHH

C OHH

CH2OH

H2

Na amalgum, H2SO4

Ribitol

CH2OH

C OHH

C OHH

C OHH

CH2OH

OHH

Ribose

78

CHO

C

C HHO

C OHH

C OHH

CH2OH

H2

Na amalgum, H2SO4

Sorbitol

CH2OH

C OHH

C HHO

C OHH

C OHH

CH2OH

OHH

Glucose

CH2OH

C = O

C HHO

C OHH

C OHH

CH2OH

CH2OH

C OHH

C HHO

C OHH

C OHH

CH2OH

H2

Na amalgum, H2SO4

Mannitol

CH2OH

C HHO

C HHO

C OHH

C OHH

CH2OH

OR

Fructose Sorbitol

Cyclitol ( inositol)

It is a cyclic hexa hydric alcohol derived from

glucose.

A member of vitamin B complex.

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H

OH

OH

H

H

OHH

OH

OHOH

H H

1

23

4

5 6

Inositol

3- Deoxysugars

Def:They are monosaccharides with only one of its

hydroxyl groups is replaced by hydrogens i.e. there is only

one oxygen missed.

Examples :

2-Deoxy-D-ribose is a constituent of DNA.

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Fucose :6 deoxy-galactose ( it is a component of

glycoprotein

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4- Amino sugars

Def:The hydroxyl group is replaced by an amino group at

the C-2 position.

Importance :Amino sugars are found in

glycosaminoglycans and glycoproteins.

Examples :

D-glucosamine:

It is a constituent of heparin and hyaluronic acid.

D-galactosamine:

It is a constituent of chondriotin sulphate.

Mannosamine

It is a constituent of neuraminic acid and sialic acids82

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O

H

OH

H

OH

H

NH2

H

OH

CH2OH

H

-D-glucoamine

2

N-acetyl-glucosamine sulfated glucosamine

O

H

OH

H

OH

H

HNH

OH

CH2OH

H

2

C CH3

O

O

H

OH

H

OH

H

NH-SO3HH

OH

CH2O-SO

3H

H

2

6

O

OH

H

H

OH

H

NH2

H

OH

CH2OH

H

2

O

OH

H

H

OH

H

HNH

OH

CH2OH

H

2

C CH3

O- D-galactosamine N- acetyl-galactosamine sulfated N-acetyl- galactosamine

OO-SO3H

H

H

OH

H

HNH

OH

CH2O - SO

3H

H

2

C CH3

O

4

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5-Amino sugar acids

Def:They are condensation products of amino sugars and

some acids

Example: Neuraminic acid

Discription: It results from a C-C bond between the C-1

of mannosamine and the C-3 of pyruvic acid.

Importance of neuraminic acid

It is amino sugar acid present in neural tissue.

The N-acetyl derivative of neuraminic (NANA) is

called sialic acid, which is widely distributed in

bacteria and animal systems

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Monosaccharides of Biological Importance

1) Glucose (Dextrose) (Grape Sugar):

It is the most important and famous sugar

It is the major source of energy in humans and animals.

Ingested carbohydrates are absorbed in the form of

glucose.

It is converted into other sugars in the liver and other

tissues

Examples : galactose, fructose, ribose and glycogen.

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2)Galactose:

It is synthesized in mammary gland to form the

disaccharide lactose (sugar of milk).

It can be converted into glucose in the liver.

3)Mannose:

It is a constituent of many glycoproteins and

aminosugar acids as sialic acid.

4)Fructose (Levulose) (Fruit Sugar):

It is present in semen

It is a constituent of disaccharide sucrose and

polysaccharide inulin.

It can be converted into glucose in the liver.

.

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5)Ribose and deoxyribose:

They form part of the structural backbone of

nucleic acids RNA and DNA.

6)Ribose enters in the structure of high-energy

phosphate compounds as ATP, GTP and CTP and

also in the structure of coenzymes such as NAD,

NADP, FAD and FMN.

7)Ribose phosphate, Ribulose phosphate, Xylulose

and sedoheptulose are intermediates in

carbohydrate metabolism

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The sugar found in DNA is

(A) Xylose

(B) Ribose

(C) Deoxyribose

(D) Ribulose

The sugar found in RNA is

(A) Ribose

(B) Deoxyribose

(C) Ribulose

(D) Erythrose

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Sorbitol is produced by reduction of :

(A) Galactose or fructose

(B) Glucose or galactose

(C) Glucose or fructose

(D) Galactose or fructose

Glucose on reduction forms

(A) Dulcitol

(B) Sorbitol

(C) Mannitol

(D) Mannitol and sorbitol90

Glucose on oxidation does not give

(A) Glycoside

(B) Glucosaccharic acid

(C) Gluconic acid

(D) Glucuronic acid

Oxidation of galactose with conc HNO3

yields

(A) Mucic acid

(B) Glucuronic acid

(C) Saccharic acid

(D) Gluconic acid91

Short Questions

Discuss shortly:

1. Define asymmetric carbon atom and enumerate properties

resulted from its presence.

2. Mention the physiological importances of carbohydrates.

3. optical activity (def,measurement,examples).

4. Classify sugars according to their optical activity.

5. optical isomerism(def,types)

6. Enentiomers (def,examples )

7. Anomers (def, examples)

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8.epimers(def, examples)

9.sugar acids (def,types & example for each)

10. sugar alcohol (def & 3 examples )

11.Deoxy-sugar ( def & 2 different examples and the

importance of each one )

12.Amino acid sugar (def,example).

13.Enumerate the products of hydrolysis of sialic

acid.

14. Enumerate monosacharides of biological

importance

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10/13/2014 94Ahmed A.Albadry

GREAT

THANKSAyman Elsamanoudy