12 Chemistry Notes Ch14 Biomolecules

8/20/2019 12 Chemistry Notes Ch14 Biomolecules

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CBSE Class-12 Chemistry Quick Revision Notes

Chapter-14: Biomolecules

• Carbohyrates:

Polyhydroxy aldehydes or polyhydroxy ketones or compounds on hydrolysis give

carbohydrates.

• Classi!ication o! carbohyrates:

Monosaccharides

a) Simplest carbohydrates

b) It cannot be hydrolysed into simpler compounds

c) Examples - Glucose mannose

!ligosaccharides

a) "arbohydrates #hich gives $ to %& monosaccharide units on hydrolysis

b)

Examples - Sucrose 'actose Maltose

Polysaccharides

a) "arbohydrates #hich on hydrolysis give large number o( monosaccharide units.

b) Examples - "ellulose starch

• "nomers:

Pair o( optical isomers #hich di((er in con(iguration only around "% atom are called anomers.

Examples - α --glucopyranose and β --glucopyranose.

• Epimers:

Pair o( optical isomers #hich di((er in con(igurationaround any other " atom other than "%

atom are called epimers. E.g. -glucose and - mannose are "$ epimers.

• #reparation o! $lucose %also calle e&trose' $rape su$ar(:

a(

)rom sucrose 12 22 11 2 6 12 6 6 12 6

cos

H

Sucrose Glu e Fructose

C H O H O C H O C H O+

+ → +

b( )rom starch

/393 ;2 3

12 22 5 2 6 12 6cos

( ) H k atm

nSucrose Glu eOr Cellulose

C H O H O nC H O+

−+ →

• Structure o! $lucose

4 2( )CHO CHOH CH OH − −

•

Structure eluciation o! $lucose:


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a( * + $lucose ,ith .

b( * + $lucose ,ith CN

c( * + $lucose ,ith N2/

( *- $lucose ,ith )ehlin$0s rea$ent

e( * + $lucose ,ith ollen0s rea$ent

!( * + $lucose ,ith nitric aci

4 2 4 4 2Saccharic acid acid

( ) ( ) ( )Oxidtion Oxidation

Gluconic

CHO CHOH CH OH COOH CHOH COOH COOH CHOH CH OH − − → − − ← − −

$( * + $lucose ,ith %CC/(2/ an 3nCl2 3 2 25( ) /

3 4 2 3 3Penta acetyl glucose

Glucose ( ) 5 shows the presence of 5 -OH groupsCH CO O ZnCl

CHO CHOCOCH CH OCOCH CH COOH → − − + →

h( * + $lucose ,ith bromine ,ater

2 water

4 2 4 2 acid

( ) ( ) Br

Gluconic

CHO CHOH CH OH COOH CHOH CH OH − − → − −

i( lucose ,ith phenyl hyra5ine to !orm osa5one


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Glucose and (ructose gives the same osa*one because the reaction takes place at "% and

"$ only.

• /ther Reactions o! lucose %#resence o! rin$ structure(

Glucose does not give Schi((+s test and does not react #ith sodium bisulphite and ,.

Pentaacetyl glucose does not react #ith hydroxyl amine. /his sho#s the absence o( 0"!

group and hence the presence o( ring structure.• Cyclic structure o! $lucose:

• a,orth representation o! $lucose:

• Cyclic structure o! !ructose:


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• a,orth representation o! !ructose

•

lycosiic linka$e:

/he oxide linkage (ormed by the loss o( a #ater molecule #hen t#o monosaccharides are

1oined together through oxygen atom is called glycosidic linkage.

• Sucrose %invert su$ar(:

a) Sucrose is a non-reducing sugar because the t#o monosaccharide units are held together

by a glycosidic linkage bet#een "% o( α -glucose and "$ o( β - (ructose. Since the

reducing groups o( glucose and (ructose are involved in glycosidic bond (ormation

sucrose is a non-reducing sugar.

b) Sucrose is dextrorotatory but on hydrolysis it gives dextrorotatory 2 laevorotatory and

the mixture is laevorotatory.

0 0 0

12 22 11 2 6 12 6 6 12 6cos

[ ] 66.5 [ ] 52.5 [ ] 92.4 D D D

H

Sucrose D glu e D fructose

C H O H O C H O C H O

α α α

+

− −

=+ =+ =−

+ → +

• a,orth #ro6ection o! Sucrose:


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• 7altose:

a) Maltose is composed o( t#o 3--glucose units in #hich "% o( one glucose 4I) is linked to

"5 o( another glucose unit 4II).

b) /he (ree aldehyde group can be produced at "% o( second glucose in solution and it sho#s

reducing properties so it is a reducing sugar.

2

1 4Maltose Glucose + Glucose

H O

C C α α →

• a,orth pro6ection o! maltose:

• 8actose %7ilk su$ar(:

It is composed o( 6--galactose and 6--glucose. /he linkage is bet#een "% o( galactose and

"5 o( glucose. ence it is also a reducing sugar.

• a,orth pro6ection o! lactose:


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• Starch:

It is a polymer o( α -glucose and consists o( t#o components 7 8mylose and

8mylopectin.

• "mylose:

a) It is a #ater soluble component

b)

It is a long unbranched chain polymerc) It contains $&& 0 %&&& α --49)- glucose units held by α - glycosidic linkages

involving "% 0 "5 glycosidic linkage

d) It constitutes about %:-$&; o( starch

• "mylopectin

a) It is a #ater insoluble component

b) It is branched chain polymer

c) It (orms chain by "% 0 "5 glycosidic linkage #hereas branching occurs by "% 0 "<

glycosidic linkage

d)

It constitutes about =&-=:; o( starch• Cellulose:

a) It occurs exclusively in plants.

b) It is a straight chain polysaccharide composed only o( β --glucose units #hich are

1oined by glycosidic linkage bet#een "% o( one glucose unit and "5 o( the next

glucose unit.

• lyco$en:

a) /he carbohydrates are stored in animal body as glycogen.

b) It is also kno#n as animal starch because its structure is similar to 8mylopectin.

c)

It is present in liver muscles and brain. d) >hen the body needs glucose en*ymes break the glycogen do#n to glucose.

• "mino acis:

8mino acids contain amino 40,$) and carboxyl 40"!!) (unctional groups.

|

2 NH

R CH COOH − −

>here ? 0 8ny side chain

Most naturally occurring amino acids have ' 0 "on(ig.


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• ypes o! amino acis:

a( Essential amino acis

/he amino acids #hich cannot be synthesised in the body and must be obtained through

diet are kno#n as essential amino acids. Examples@ Aaline 'eucine

b( Non-essential amino acis

/he amino acids #hich can be synthesised in the body are kno#n as non-essential

amino acids. Examples@ Glycine 8lanine

• 3,itter ion !orm o! amino acis:

a)

8mino acids behave like salts rather than simple amines or carboxylic acids. /hisbehaviour is due to the presence o( both acidic 4carboxyl group) and basic 4amino group)

groups in the same molecule. In aBueous solution the carboxyl group can lose a proton

and amino group can accept a proton giving rise to a dipolar ion kno#n as *#itter ion.

/his is neutral but contains both positive and negative charges.

b) In *#itter ionic (orm amino acids sho# amphoteric behaviour as they react both #ith

acids and bases.

|| ||

| |

:

( ion)2 3

Zwitter

O O

NH NH

R CH C O H R CH C O+

−− − − − ⇔ − − −

• .soelectronic point:

/he p at #hich the dipolar ion exists as neutral ion and does not migrate to either electrode

cathode or anode is called isoelectronic point.

• #roteins:

Proteins are the polymers o( α -amino acids and they are connected to each other by

peptide bond or peptide linkage. 8 polypeptide #ith more than hundred amino acid residues

having molecular mass higher than %&&&&u is called a protein.

• #eptie linka$e:Peptide linkage is an amide linkage (ormed by condensation reaction bet#een 0"!! group

o( one amino acid and 0,$ group o( another amino acid.

1

||

2 2 2| | | |

2 1 2 R

O

R R R

H N CH COOH H N CH COOH H N CH C NH CH COOH − − + − − → − − − − −

Peptide link age

• #rimary structure o! proteins:

/he seBuence o( amino acids is said to be the primary structure o( a protein.


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• Seconary structure o! proteins: It re(ers to the shape in #hich long polypeptide chain can

exist. /#o di((erent types o( structures@

α 0 elix@

a) It #as given by 'inus Pauling in %C:%

b)

It exists #hen ?- group is large.

c) ?ight handed scre# #ith the , group o( each amino acid residue 0 bonded to 0 "

D ! o( ad1acent turn o( the helix.

d) 8lso kno#n as .aals (orces

• ,o shapes o! proteins:

ibrous proteins

a) >hen the polypeptide chains run parallel and are held together by hydrogen and

disulphide bonds then (ibre0 like structure is (ormed.

b) /hese proteins are generally insoluble in #ater

c) Examples@ keratin 4present in hair #ool silk) and myosin 4present in muscles) etc

Globular proteins

a) /his structure results #hen the chains o( polypeptides coil around to give a spherical

shape.

b) /hese are usually soluble in #ater.

c) Examples@ Insulin and albumins


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• Quaternary structure o! proteins:

a) Some o( the proteins are composed o( t#o or more polypeptide chains re(erred to as sub-

units.

b) /he spatial arrangement o( these subunits #ith respect to each other is kno#n as

Buaternary structure o( proteins.

• *enaturation o! proteins:

a) /he loss o( biological activity o( proteins #hen a protein in its native (orm is sub1ected to

physical change like change in temperature or chemical change like change in p. /his is

called denaturation o( protein.

b) Example@ coagulation o( egg #hite on boiling curdling o( milk.

• Nucleosie:

a) Hase 9 sugar

• Nucleotie:

a) Hase 9 sugar 9 phosphate group

• Nucleic acis %or polynucleties(:

a) 'ong chain polymers o( nucleotides.

b) ,ucleotides are 1oined by phosphodiester linkage bet#een :+ and + " atoms o( a pentose

sugar. • ,o types o! nucleic acis:

*N"

a) It has a double stranded α -helix structure in #hich t#o strands are coiled spirally in

opposite directions.

b) Sugar present is β 00$-deoxyribose

c) Hases@

i) Purine bases@ 8denine 48) and Guanine 4G)

ii) Pyrimidine bases@ /hymine 4/) and cytosine 4")

d)

It occurs mainly in the nucleus o( the cell.


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e) It is responsible (or transmission (or heredity character.

RN"

a) It has a single stranded α -helix structure.

b) Sugar present is β 00ribose

c)

Hases@

i) Purine bases@ 8denine 48) and Guanine 4G)

ii) Pyrimidine bases@ racil 4) and cytosine 4")

d) It occurs mainly in the cytoplasm o( the cell.

e) It helps in protein synthesis.

• *ouble heli& structure o! *N":

a) It is composed o( t#o right handed helical polynucleotide chains coiled spirally in

opposite directions around the same central axis.

b) /#o strands are anti-parallel i.e. their phosphodiester linkage runs in opposite

directions.

c) Hases are stacked inside the helix in planes ⊥ to the helical axis.

d) /#o strands are held together by 0 bonds 48 D / G ≡ ").

e) /he t#o strands are complementary to each other because the hydrogen bonds are

(ormed bet#een speci(ic pairs o( bases.

f) 8denine (orms hydrogen bonds #ith thymine #hereas cytosine (orms hydrogen bonds

#ith guanine.

g) iameter o( double helix is $ nm.

h) ouble helix repeats at intervals o( .5 nm. 4!ne complete turn)

i)

/otal amount o( purine 48 9 G) D /otal amount o( pyramidine 4" 9 /)

• itamins:

Aitamins are organic compounds reBuired in the diet in small amounts to per(orm speci(ic

biological (unctions (or normal maintenance o( optimum gro#th and health o( the organism.

• Classi!ication o! vitamins:

Aitamins are classi(ied into t#o groups depending upon their solubility in #ater or (at.

a) >ater soluble vitamins

i) /hese vitamins are soluble in #ater.

ii) >ater soluble vitamins must be supplied regularly in diet because they are readily

excreted in urine and cannot be stored 4except vitamin H%$) in our body.iii) Example@ Aitamin " H group vitamins.

b) at soluble vitamins

i) /hese vitamins are soluble in (at and oils but insoluble in #ater.

ii) /hey are stored in liver and adipose 4(at storing) tissues.

iii) Example@ Aitamin 8 E and J


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• .mportant vitamins' their sources an their e!iciency iseases:

Name o! vitamins Sources *e!iciency iseases

Aitamin 8 ish liver oil carrots

butter and milk

xe r o p h t h a l m i a

4hardening o( cornea o(

eye)

,ight blindness

Aitamin H%

4/hiamine)

Keast milk green

vegetables and cereals

Heri beri 4loss o( appetite

retarded gro#th)

Aitamin H$

4?ibo(lavin)

Milk egg #hite liver

kidney

"heilosis 4(issuring at

corners o( mouth and

lips) digestive disorders

and burning sensation

o( the skin.

Aitamin H<

4Pyridoxine)

Keast milk egg yolk

cereals and grams

"onvulsions

Aitamin H%$ Meat (ish egg and

curd

Pernicious anaemia

4?H" de(icient in

haemoglobin)

Aitamin "

48scorbic acid)

"itrus (ruits amla and

green lea(y vegetables

Scurvy 4bleeding gums)

Aitamin Exposure to sunlight

(ish and egg yolk

?ickets 4bone de(ormities

in children) and

osteomalacia

4so(t bones and

1oint pain in adults)

Aitamin E Aegetable oils like #heat

germ oil sun(lo#er oil

etc.

Increased (ragility o(

?H"s and muscular

#eakness

Aitamin J Green lea(y vegetables Increased blood clotting

time

12 Chemistry Notes Ch14 Biomolecules

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