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Biomolecules 1 C O N S E R V A T I O N L A W

All living systems (plants and animals) are composed of several non living molecules which are presentin their cells in a very complex but highly organised manner are called Biomolecules.

e.g. Carbohydrates, Proteins, Nucleic acids, Lipids etc.

Biomolecules Cell organells Cells Tissues Organs Living system

CARBOHYDRATES (Molecules of Support and Energy)

They are composed of C, H and O

Ratio of hydrogen and oxygen in carbohydrates is 2 : 1 therefore carbohydrates are known ashydrates of carbon.

General formula Cx (H2O)y

Glucose C6H

12O

6or C

6(H

2O)

6

Sucrose C12

H22

O11

or C12

(H2O)

11

Starch C6H

10O

5or [C

6(H

2O)

5]

n

Exceptions

(i) Carbohydrates in which ratio of H and O is not 2 : 1

e.g. Rhamnose C6H

12O

5

De-oxyribose C5H

10O

4

(ii) Compounds in which ratio of H and O is 2 : 1 but they are not carbohydrates

e.g. Formaldehyde H-CHO or CH2O

Acetic acid CH3COOH or C

2H

4O

2

Lactic acid C3H

6O

3

Definition

Carbohydrates may be defined as optically active polyhydroxy aldehydes or ketones

or the compounds which produce such units on hydrolysis.

Note

Carbohydrates are also known as Saccharides because of the sweet taste of sugars

(Latin, sekcharon means sugar)



Classification of Carbohydrates

On the basis of their behaviour on hydrolysis

Monosaccharides Oligosaccharides Polysaccharides

A carbohydrate that cannot be Carbohydrates that yield 2 to10 Carbohydrates which yield a

hydrolysed further to give simpler monosaccharide units, on hydrolysis, are large number of monosaccharide

unit of polyhydroxy aldehyde or called oligosaccharides.They are further units on hydrolysis are called

ketone is called a monosaccharide. classified as disaccharides, trisaccharides, polysaccharides

About 20 monosaccharides are tetrasaccharides, etc., Amongst these They are of two types

known to occur in nature. the most common are disaccharides. (a) Homo polysaccharides

e.g. Glucose, e.g. Disacc-Sucrose, Maltose,Lactose e.g.,Starch, Cellulose, Glycogen

Fructose, Trisacc-Raffinose (b) Hetero polysaccharides

Ribose, etc Tetrasacc- Stachyose e.g., Gum

Examples

DisaccharidesHydrolysis

12 22 11 6 12 6 6 12 6

Sucrose Glu cos e Fructose

C H O C H O C H O


12 22 11 6 12 6 6 12 6

Maltose Glu cos e Glu cos e

C H O C H O C H O


12 22 11 6 12 6 6 12 6

Lactose Galactose Glu cos e

C H O C H O C H O

TrisaccharidesHydrolysis

18 32 16 6 12 6 6 12 6 6 12 6

Raffinose Glu cos e Fructose Galactose

C H O C H O C H O C H O

TetrasaccharidesHydrolysis

24 42 21 6 12 6 6 12 6 6 12 6 6 12 6

Stachyose Glu cos e Fructose Galactose Galactose

C H O C H O C H O C H O C H O

Polysaccharides Hydrolysisn56 10 6 12 6

Starch D Glucose(C H O ) n C H O

Polysaccharides Hydrolysisn56 10 6 12 6

Cellulose D Glucose(C H O ) n C H O

On the basis of physical properties

Sugars Non-sugars

Crystalline solids Amorphous solids

Sweet in taste Tasteless

Water soluble Water insoluble

e.g. Glucose, Fructose,Sucrose etc. e.g. Starch, Cellulose, Glycogen etc.



Sugars are further classified in two parts

Reducing Sugars Non-Reducing Sugars

They have free aldehyde or ketonic group and In disaccharides, if the reducing groups of

they reduces Tollens Reagent & Fehling solution monosaccharides i.e., aldehydic or ketonic

e.g. Monosaccharides - All are reducing groups are bonded, these are non-reducing

Disaccharides -Maltose, Lactose are reducing sugars e.g. Sucrose

Carbohydrates

Sugars Non-sugars(Polysaccharides)

Monosacc-harides

Oligosacc-harides

Aldoses Ketoses

Disacc-harides

Trisacc-harides

Tetrasacc-harides

Homopoly-saccharides

Heteropoly-saccharides

... ... ...

MONOSACCHARIDES

Monosaccharides are further classified on the basis of numberof carbon atoms and the functional group present in them.

If a monosaccharide contains an aldehyde group, it is known as an aldose and if it contains a keto group, it is

known as a ketose.

Number of carbon atoms constituting the monosaccharide is also introduced in their name.

They have 3 to 7 carbon atoms.

C atoms General term Aldehyde Ketone

3 Triose Aldotriose Ketotriose

4 Tetrose Aldotetrose Ketotetrose

5 Pentose Aldopentose Ketopentose

6 Hexose Aldohexose Ketohexose

7 Heptose Aldoheptose Ketoheptose

Different Types of Monosaccharides

Except ketotriose (dihydroxy acetone), all aldoses and ketoses (monosaccharides) contain asymmetric carbonatoms and are optically active.Number of isomers depend on the number of asymmetric carbon atoms in the molecule of monosaccharide and is

derived by the formula 2n , where n is the number of asymmetric carbon atoms in the molecule.

e.g. Glucose n = 4 and number of isomers = 42 = 16Configuration of monosacccharides :All the naturally occurring monosaccharides belong to D-series, i.e., the –OH group is on the right side of thelowest asymmetric carbon atom as in D(+) glyceraldehyde.



GLUCOSE / Dextrose/ Grape Sugar/ Blood Sugar

(a) Glucose occurs freely in nature as well as in the combined form.

(b) It is present in sweet fruits and honey. Ripe grapes also contain glucose in large amounts.

(c) Glucose is also known as dextrose because naturally occuring glucose is dextrorotatory.

Preparations of glucose

(i) From Sucrose(Cane Sugar)

If sucrose is boiled with dil HCl or H2SO

4 in alcoholic solution, glucose and fructose are obtained in equal amounts.

+H12 22 11 2 6 12 6 6 12 6

Sucrose Glucose Fructose

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

(ii) From Starch

Commercially glucose is obtained by hydrolysis of starch by boiling it with dilute H2SO

4 at 393 K

6 10 5 2 6 12 6393 ,2 3Starch or Cellulose Glucose

(C H O ) + nH O C H OHn K atm

n

General reactions of glucose It has one aldehyde group, one primary 2CH OH and four secondary

CH OH| alcoholic groups. It shows following reactions

(i) Reaction with HI (Reduction)

This reaction suggesting all the six carbon of glucose are linked in a straight chain.

(ii) Reaction showing presence of carbonyl group

Glucose reacts with hydroxylamine to form an oxime and adds a molecule of hydrogen cyanide to give cyanohy-drin. These reactions confirm the presence of a carbonyl group (>C = 0) in glucose.

(iii) Reaction which indicates presence of –CHO groupGlucose gets oxidised to six carbon carboxylic acid (gluconic acid) on reaction with a mild oxidising agent likebromine water. This indicates that the carbonyl group is present as an aldehyde group.

Glucose is probably most

abundant organic compound on earth



(iv) Reaction showing presence of five – OH groupsAcetylation of glucose with acetic anhydride gives glucose pentaacetate which confirms the presence of five –OHgroups. Since it exists as a stable compound, five –OH groups should be attached to different carbon atoms.

(v) Reaction showing presence of one primary alcoholic group

On oxidation with conc.nitric acid, glucose as well as gluconic acid both yield a dicarboxylic acid, saccharic acid.This indicates the presence of a primary alcoholic (–OH) group in glucose.

Structure of glucose

Open Chain Structure

D indicates that –OH of the last asymmetric carbon (C5) is at the right side.

+ represents dextrorotary nature i.e. it rotate PPL in clock wise direction.

Cyclic Structure

The open chain structure of glucose explained most of its properties but fails to explain the following

1. Glucose does not react with NaHSO3and NH

3.

2. Even though an aldehyde group is present, glucose does not give 2,4-DNP test & Schiff test.

3. Glucose does not react with Grignard reagent.

4. Glucose pentaacetate does not react with hydroxylamine.

5. Glucose exist in two different crystalline forms which are named as and .

All these observations indicate that free aldehyde group is not present in the molecule.

Fischer projection formula

It was proposed that a hemiacetal is formed by reaction of –CHO and –OH group of C-5 of glucose.



The two cyclic hemiacetal forms of glucose differ only in the configuration of the hydroxyl group at C1, called

anomeric carbon (the aldehyde carbon before cyclisation). Such isomers, i.e., -form and -form, are called

anomers.

The six membered cyclic structure of glucose is called pyranose structure or in analogy with pyran.

Pyran is a cyclic organic compound with one oxygen atom and five carbon atoms in the ring. The cyclic structure

of glucose is more correctly represented by Haworth structure as given below.

Pyranose (Haworth) Strucutre

FRUCTOSE / Laevulose/ Fruit Sugar/ Sweetest Sugar

(a) It is present in abundance in fruits and hence is called fruit sugar.

(b) It is also present in cane sugar and honey along with glucose in combined form.

(c) The polysaccharide inulin is a polymer of fructose.

(d) Fructose is also known as laevulose because naturally occuring glucose is laevorotatory.

Structure of fructose

Open Chain Structure



Closed Chain Structure

A hemiacetal is formed by reaction of –CO– and –OH group of C-5 of fructose.

Fischer projection formula

Furanose (Haworth) Strucutre

The ring, thus formed is a five membered ring and is named as furanose with analogy to the compound furan.

Furan is a five membered cyclic compound with one oxygen and four carbon atoms.

DISACCHARIDES

Disaccharides on hydrolysis with dilute acids or enzymes yield two molecules of either the same or differentmonosaccharides.

The two monosaccharides are joined together by an oxide linkage formed by the loss of a water mol-ecule.

Such a linkage between two monosaccharide units through oxygen atom is called glycosidic linkage.

SUCROSE

(i) Sucrose is a white crystalline solid, soluble in water.

(ii) When heated above its melting point, it forms a brown substance known as caramel.

(iii) Concentrated sulphuric acid chars sucrose, the product being almost pure carbon.

(iv) A glycosidic linkage between C1 of -glucose and C2 of -fructose.

Since the reducing groups of glucose and fructose are involved in glycosidic bond formation, sucroseis a non reducing sugar.



(v) Hydrolysis

D D D0 0 0

dil acid or12 22 11 2 6 12 6 6 12 6Invertase

( )Sucrose ( ) Glu cose ( ) fructose66.5 52.5 92.4[ ] [ ] [ ]

C H O H O C H O C H O

Sucrose is dextrorotatory but after hydrolysis gives dextrorotatory glucose and laevorotatory fructose.

Since the laevorotation of fructose (–92.4°) is more than dextrorotation of glucose (+ 52.5°), the mixture islaevorotatory.

Thus, hydrolysis of sucrose brings about a change in the sign of rotation, from dextro (+) to laevo (–) and theproduct is named as invert sugar & the hydrolysis of sucrose is known as inversion of sugar.

MALTOSE

Maltose is composed of two -D-glucose units in which C1 of one glucose (I) is linked to C4 of another glucose

(II).

The free aldehyde group can be produced at C1 of second glucose in solution and it shows reducing properties so

it is a reducing sugar.

Hydrolysis

dil acid or12 22 11 2 6 12 6Maltase

Maltose D Glu coseC H O H O 2C H O

LACTOSE

It is more commonly known as milk sugar since this disaccharide is found in milk.

It is composed of -D- galactose and -D-glucose.

The linkage is between C1 of galactose and C4 of glucose. Hence it is also a reducing sugar.



Hydrolysis

dil acid or12 22 11 2 6 6 6 6 12 6Lactase

Lactose D Glu cose D GalactoseC H O H O C H O C H O

Summary of Disaccharides

Sugar Common Name Enzyme Hydrolysis Product Nature

Sucrose Cane sugar Invertase D-Glucose + D-Fructose Nonreducing

(C1-C

2 Glycosidic Bond)

Maltose Malt sugar Maltase D-Glucose + D-Glucose Reducing

(C1-C

4Glycosidic Bond)

Lactose Milk sugar Lactase D-Galactose + D-Glucose Reducing

(C1-C

4Glycosidic Bond)

POLY SACCHARIDES

Polysaccharides contain a large number of monosaccharide units joined together by glycosidic linkages.

These are the most commonly encountered carbohydrates in nature.

They mainly act as the food storage or structural materials.

STARCH / Amylum

(a) Starch is the main storage polysaccharide of plants.

(b) It is the most important dietary source for human beings.

(c) High content of starch is found in cereals, roots, tubers and some vegetables.

(d) It is a polymer of -glucose

(e) It has two components

(i) Amylose

Amylose is water soluble component which constitutes about 15-20% of starch.

Chemically amylose is a long unbranched chain with 200-1000 -D-(+)-glucose units held by C1– C4 glyco-sidic linkage.



(ii) Amylopectin

Amylopectin is insoluble in water and constitutes about 80-85% of starch.

It is a branched chain polymer of -D-glucose units in which chain is formed by C1–C4 glycosidic linkagewhereas branching occurs by C1–C6 glycosidic linkage.

GLYCOGEN /Animal Starch

(a) It is homopolymer of-D-glucose

(b) The carbohydrates are stored in animal body as glycogen.

(c) It is also known as animal starch because its structure is similar to amylopectin and is rather more highlybranched.

(d) It is present in liver, muscles and brain.

(e) When the body needs glucose (like fast or illness), enzymes break the glycogen down to glucose.

(f) Glycogen is also found in yeast and fungi.



CELLUOSE

(a) It is homopolymer of-D-glucose.

(b) C1-C

4 glycosidic bond.

(c) Unbranched, water insoluble polymer.

(d) It is predominant constituent of cell wall of plant cells.

INULIN It is polysaccharide of -fructose.

GUM It is polymer of sugar except glucose.

Importance of Carbohydrates

(a) Carbohydrates are essential for life in both plants and animals. They form a major portion of our food.

(b) Honey has been used for a long time as an instant source of energy by ‘Vaids’ in ayurvedic system of medicine.(c) Carbohydrates are used as storage molecules as starch in plants and glycogen in animals.

(d) Cell wall of bacteria and plants is made up of cellulose.

(e) We build furniture, etc. from cellulose in the form of wood and clothe ourselves with cellulose in the form ofcotton fibre.

(f) They provide raw materials for many important industries like textiles, paper, lacquers and breweries.

Most abundant organic

substance in plant

kingdom



SOME IMPORTANT FACTS RELATED TO CARBOHYDRATES 1. Action with phenylhydrazine (Osazone formation)

Glucose contains an aldehyde group and is expected to react with phenyl hydrazine to form phenyl hydrazone.However, when the excess of phenyl hydrazine is used, the product formed is an osazone i.e., glucosazone.

Osazone formation is used in identification of carbohydrates.

hydroxy aldehyde and hydroxy Ketone also form osazone.

Only first two carbons participate in formation of osazone. Remaining molecule become unchanged. Therefore

hexose which has same configuration at 3 4,C C and 5 C forms same osazone. Thus Glucose, Fructose and

Mannose forms same osazone.

2. Reaction with alkaliesWhen warmed with concentrated alkali, glucose first turns yellow, then brown and finally gives resionousmass.

When a dil solution of glucose is warmed withdil solution of alkali., some glucose is converted into fructoseand mannose. This reaction is called

LOBRY DE BRUYN VAN EKENSTEIN REARRANGEMENT

Glucose

Fructose Mannose

The same equilibrium mixture is obtained even it starts with mannose or fructose.

Due to this reaction fructose reduces F.S., B.S. and T.R. (alkaline medium)

3. Reaction with CH3OH in presence of dry HCl

Both glucose and fructose on treatment with CH3OH/dry HCl gas forms and methyl glucosides and

fructosides respectively indicating that one of the –OH group is different in and structures

(supports the cyclic structure).



4. MutarotationIt is the change of optical rotation of an optically active compound in solution with time

5. Reducing SugarThey have free aldehyde or ketonic group and show following reactions

(a) They reduces Tollens Reagent, Fehling solution & Benedict solution

(b) They form oxime with hydroxyl amine.

(c) They form osazone with phenyl hydrazine.

(d) They show Mutarotation.

6. Sucrose is more useful for preserving jams and jellies because it is a non-reducing sugar so is not easilyoxidised. Glucose, in contrast is a reducing sugar, so it will oxidise and spoil the jams and jellies.

7. Glucose reacts with HCN, NH2OH and C

6H

5NHNH

2but does not react with NH

3, NaHSO

3, 2, 4-DNP and

Schiff's reagent

Explaination : Please note that the glucose ring is not very stable. It can be easily cleaved by strong reagentssuch as HCN, NH

2OH and NH

2OH and C

6H

5NHNH

2 etc. to give the intermediate open chain structure

containing a free aldehydic group. It gives all the characteristic reactions with the reagents listed above. How-ever, weak reagents like NH

3 and NaHSO

3are unable to cleave the ring structure and therefore, the cyclic

structure fails to react with these.

8. Reduction with Na-Hg/H2O or NaBH

4, glucose forms D-sorbitol while fructose gives a mixture of D-sorbitol

and D-mannitol.

9. AnomersThey are opticals isomers whose structure differ in the position of a group at a carbon atom of aldehyde orketone e.g.and forms of glucose and fructose are anomers. C-1 in glucose and C-2 in fructose is calledanomeric carbon.


Biomolecules 14 C O N S E R V A T I O N L A W10. Epimers

They are opticals isomers whose structure differ in the position of a group at a carbon atom other than anomericcentre. e.g. Glucose and Mannose are C

2 epimers. Glucose and Galactose are C

4 epimers.

11. Invert SugarEquimolar mixture of glucose and fructose obtained from sucrose is called invert sugar. It has no sucrose at all.

12. In our body 1 mole of glucose produces 38 ATP which is the effeiciency (38%) of our body. In our body,energy is actually stored in the form of ATP.

13. Synthesis of each molecule of glucose in photosynthesis involves 18 molecules of ATP.

h2 2 6 12 6 2glu cose

6CO 6H O 18ATP C H O 6O

14. Simplest carbohydrate is glyceraldehyde. It has one chiral carbon.

15. Relative sweetnessFructose > Invert Sugar > Sucrose > Glucose > Maltose > LactoseFructose is sweetest sugar

16. Our blood contains 60 to 100 mg of glucose per 100 mL of blood. This quantity is regulrly maintained by the

protein hormone insulin secreted by cells of pancrease.

17. Starch solution gives a blue colour with a drop of iodine which disappears on heating and reappears on cooling.

18. Starch and Cellulose are not fermented by yeast.

19. It may be noted that cellulose cannot be hydrolysed in our body because cellulase enzymes required for itshydrolysis are not present in our body, hence, cellulose is not digestible. However, grazing animals (such ascow, buffalo and deer, etc.) can used cellulose of grass and plants as food by converting them into glucose.

20. Carbohydrates act as lubricants in joints.

21. Starch is finally converted to glucose in intestine.

22. The only non-reducing disaccharide is sucrose.

biomolecules - masters academy · 2020. 9. 28. · masters academy 1- anasagar circular road, opp....

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