Carbohydrates I

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Introduction to Biochemistry

Carbohydrates


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Definition

Carbohydrates are the

polyhydroxyl alcohols

with functional

aldehydrate or ketonegroups.


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Carbohydrates

Carbohydratesare

a major source of energy

from our diet.

composed of the elements

C, H and O with a general

formula i.e. CnHnOn.

also called saccharides,which means !sugars."


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Carbohydrates

Carbohydrates

are produced by

photosynthesis in plants.

such as glucose aresynthesi#ed in plants

from CO, HO, and

energy from the sun.

are oxidi#ed in li$ing cellsto produce CO, HO, and

energy.


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Biomedical Importance of

Carbohydrates

%. &ro$ide major source of energy '(.%C)

. *la$or and +weeteners.

. Dietary fiber 'Cellulose).

(. -reakdown of fatty acids and pre$enting ketosis


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. /egulation of $arious metabolic processes in the body askey molecules in the central metabolic pathways of thebody.

0.+torage form of food in plants as starch.

1. +er$e also as stored forms of energy as glycogen in li$erand muscles.

2. &rotection of bacterial cells as bacterial cell wallpolysaccharides, made up of muerin '34acetyl

nuramic acid '3535), 34acetyl glucosamine, andse$eral other amino acids linked by peptide linkage).

6. 7mportant components of brain cells as neuraminicacids, cerebrosides '8lycolipids) and gangliosides


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%9. 7mportant component of nucleic acids aspentose sugars ribose and deoxyribose.

%%. :any glucosides 'Carbohydrate deri$ati$efrom plants) are important drugs, such asglucoside of digitaliswhich is utili#ed for thetreatment of heart

diseases. %. Carbohydrates are essential components of

milk, especially lactose.


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%. :any glucosides 'Carbohydrate deri$ati$e

from plants) are important drugs, such as

glucoside of digitalis which is utili#ed for thetreatment of heart diseases.

%(. Carbohydrates are essential components of

milk, especially lactose.

%. -iological recognition processes of

immunoglobulins and self :HCs.


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Classification of Carbohydrates

Carbohydrates can be classified in to four categoriesaccording to number of carbon atoms.

a4:onosaccharide

b4Disaccharidec4Oligosaccharide

d4&olysaccharide


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Monosacch:onosaccharidearides

Monosaccharides:

;hey are classified according to the

number of carbon atoms present.

;hey are the simplest sugars

;hey cannot be hydroly#ed further.

;hey may be aldoses or ketoses. 5ll the monosaccharides are reducing

sugars.


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Sugars

Aldosesare monosaccharides

with an aldehyde group

Ketosesare monosaccharides

with a ketone group


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Monosaccharide

A Aldehyde group B Keto group

H

C


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Generic names Aldose Ketos

Carbons> trioses 8lyceraldehyde Dihydroxy acetone

( Carbons> tetroses =rythrose =rythrulose

Carbons> pentoses /ibose /ibulose

0 Carbons> hexoses 8lucose *ructose

1 Carbons> heptoses 8lucoheptose +edoheptulose

6 Carbons> nonoses 3euraminic acid


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8lycosidic -ond

:onosaccharides can be linked byglycosidic bonds to creates largerstructure.

Eample:

:altose>

;wo molecules of glucose are attached

with one another through a glycolic linkageof C no % of one glucose and C no ( ofother.'? %4( linkage)


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Eamples ofMonosaccharides

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&ublishing as -enjamin Cummings


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!"Glucose

Glucose8rape sugarDextrose

Dextro4rotation:ost commonsource sucrosewhich is table sugar

*irst line ofnutrition forproduction ofenergy.


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:onosaccharides

Glucose #Cont$%*-+ 09 A %99 mgBdl

/-+ %99 A %09 mgBdl

On reduction glucose forms alcohol e.g. +orbitolOn oxidation sugar acids '8luconic acid)

8luconic acid 7f oxidation of C% of glucose

7t needs insulin for its entry in to cell. '&roper Care

+hould be taken to gi$e to diabetic patient)3ormally it does not appear in urine but in diabetes

mellitus glucose passes out in urine.


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!"&ructose

!"fructose is a ketoheose C'()*+'$

is the s,eetestcarbohydrate$

is found in fruit -uices andhoney$

con.erts to glucose in thebody$

/ure honey is made up offructose only$

It does not need insulin forits enter in to cell0 therefore

e.en diabetic pt$ can takeit$

It is present in appreciableamount in seminal fluidand act as source of energyfor spermato1oa$

H OH

CHOH

C

HO

H OH

H

C

O

C

C

CHOH

D4*ructose


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Galactose

:ain source actose which is milk sugar

tili#ed in de$elopment of brain tissue.

e.g. Cerebroside and 8angliosides

Mannose

Can be con$erted to glucoseOn reduction forms :annitol


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!isaccharides


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Important !isaccharides

5 disaccharideconsists of two monosaccharides.

Monosaccharides !isaccharide

glucose E glucose maltose E HO

glucose E galactose lactose E HO

glucose E fructose sucrose E HO


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Maltose

Maltoseis

a disaccharide also known as malt sugar. composed of two D4glucose molecules.

obtained from the hydrolysis of starch. used in cereals, candies, and brewing. found in both the 4 and4 forms.

&roduced from starch by hydrolysis due to sali$ary F

pancreatic amylase. Hydroly#ed by :altase


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&ormation of Maltose

*ree 4OH


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2actose

2actose

is a disaccharide of-D-galactose and - or

4D4glucose.

contains a4%,(4glycosidic bond.

is found in milk and

milk products. /educing sugar

Hydroly#ed by actase

?4form-form


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Sucrose

Sucroseor table sugar is obtained from sugar cane and sugar beets.

consists of -D4glucose and-D-fructose..

has an ,4%,4glycosidic bond.

3on4reducing3on4reducing

sugarsugar 7n$ert sugar7n$ert sugar

Hydroly#ed byHydroly#ed by

+ucrase '7n$ertase)+ucrase '7n$ertase)

"!"glucose

"!"fructose


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Oligosaccharide

Contain from to about %9

monosaccharide units.

;hey are of less significance.

=xamples>

:altotriose


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/olysaccharides

Copyright @ 99 by &earson =ducation, 7nc.

&ublishing as -enjamin Cummings


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/olysaccharides

/olysaccharides

;hese molecules contain more than

%9 monosaccharide units and can be

%99 of sugar units in length.

;hey can be further classified into

Homopolysaccharide

Heteropolysaccharide


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(omopolysaccharide

;hese molecules contain same

monosaccharide units.

=xamples>a. +tarch

b. 8lycogen

c. Dextrins

d. Dextrans

e. Cellulose


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!etrans

;hey are $iscous polysaccharides

;hey are used as plasma expanders

in the treatment of shock.Inulin

7nulin 'Homopolysacharide) is used for

clinical purposes in clearance tests.

7t is also used in diagnosis of 8*/

'glomerular filtration rate)


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Starch

:ajor storagecarbohydrate in higherplants

5mylose A long straight

glucose chains 'a%4() 5mylopectin A

branched e$ery (49

glc residues 'a %40) &ro$ides 29G of

dietary calories inhumans worldwide


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Structures of Amylose and

Amylopectin


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Amylose

Amyloseis

a polymer of ?4D4

glucose molecules.

linked by 4%,(

glycosidic bonds.

a continuous

'unbranched) chain.


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Amylopectin

Amylopectin

is a polymer of ?4D4

glucose molecules.

is a branched4chain

polysaccharide.

has ?4%,(4glycosidic

bonds between the

glucose units.

has 4%,0 bonds to

branches.


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Glycogen

Glycogen

:ajor storage carbohydrate in:ajor storage carbohydrate inanimals li$er and muscles.animals li$er and muscles.

ong straight glucose chainsong straight glucose chains

'a%4()and 'a %40) linkages.'a%4()and 'a %40) linkages. ;herefore it needs en#ymes.;herefore it needs en#ymes.

a.a. &hosphorylase 'which break %4&hosphorylase 'which break %4( glycosidic bond).( glycosidic bond).

b.b. Debranching en#ymes 'breaksDebranching en#ymes 'breaks

%40 bond)%40 bond) :ore branched than starch:ore branched than starch

-lood glucose le$els are usuallymaintained by i$er glycogen


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Dextrins

+tarches like amylose and amylopectin

hydroly#e to dextrins 'smaller

polysaccharides)

Contain 42 glucose units


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Cellulose

Cellulose is a polysaccharide

of glucose units inunbranched chains.

has4%,(4glycosidicbonds. cannot be digested

by humans becausethey lack the en#ymeCellulase.

7t pro$ides bulk tofood and stimulatethe intestinalperistalsis thuspre$ent constipation.


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(etero /olysaccharides

Contain same type of monosaccharides or

different monosaccharides along with

prosthetic groups.

=xamples>

:uco &olysaccharides

:ucilagesHemicellulose


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Muco /olysaccharides

Hyaluronic acid

HeparinChondroitin sulphate

-lood group &olysaccharides.

+erum mucoids


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Mucilages

5gar

egetable gums

&ectin(emicellulose

Carbohydrates I

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