Carbohydrates

Home Science Carbohydrates

CARBOHYDRATES

Dr. Daxaben N. MehtaPrincipal

Smt. Sadguna C.U.Shah Home Science and C. U. Shah Arts & Commerce Mahila College,

Wadhwancity, Dist: Surendranagar


CARBOHYDRATES

Term carbohydrate is derived from the French: hydrate de carbonecompounds composed of C, H, and O (CH2O)n when n = 5 then C5H10O5not all carbohydrates have this empirical formula: deoxysugars, aminosugarscarbohydrates are the most abundant compounds found in nature (cellulose: 100 billion tons annually)


characteristics

• Most carbohydrates are found naturally in bound form rather than as simple sugars

• Polysaccharides (starch, cellulose, inulin, gums)• Glycoproteins and proteoglycans (hormones, blood

group substances, antibodies)• Glycolipids (cerebrosides, gangliosides)• Glycosides• Mucopolysaccharides (hyaluronic acid)• Nucleic acids


Functions

• sources of energy• intermediates in the biosynthesis of other basic

biochemical entities (fats and proteins)• associated with other entities such as glycosides,

vitamins and antibiotics)• form structural tissues in plants and in

microorganisms (cellulose, lignin, murein)• participate in biological transport, cell-cell

recognition, activation of growth factors, modulation of the immune system


Classification

• Monosaccharides (monoses or glycoses)• Trioses, tetroses, pentoses, hexoses

• Oligosaccharides• Di, tri, tetra, penta, up to 9 or 10 • Most important are the disaccharides

• Polysaccharides or glycans• Homo and Heteropolysaccharides• Complex carbohydrates


Monosaccharides

• also known as simple sugars• classified by 1. the number of carbons and

2. whether aldoses or ketoses• most (99%) are straight chain compounds• D-glyceraldehyde is the simplest of the

aldoses (aldotriose)• all other sugars have the ending ose

(glucose, galactose, ribose, lactose, etc…)


Properties• Differences in structures of sugars are

responsible for variations in properties• Physical Crystalline form; solubility; rotatory power• Chemical Reactions oxidations, reductions, condensations• Physiological Nutritive value (human, bacterial); sweetness; absorption


Structure of aldose and ketose


C

C

CH2OH

OH)n(H

O

H

Aldose

C

C

CH2OH

OHH

O

H

Aldotriosen = 1

C

CH2OH

OHH

C O

H

C OHH

Aldotetrosen = 2

C

CH2OH

OHH

C O

H

C OHH

C OHH

Aldopentose n = 3

C O

H

C OHH

C OHH

CH OH

C

CH2OH

OHH

Aldohexose n = 4

Aldose sugars


C

C

CH2OH

OH)n(H

O

CH2OH

Ketose

CH2OH

C O

CH2OH

Ketotriose n = 0

CH2OH

C O

C OHH

CH2OH

Ketotetrose n = 1

C OHH

CH2OH

CH2OH

C O

C OHH

Ketopentose n = 2

C OHH

CH2OH

CH2OH

C O

C OHH

OHH

Ketohexose n = 3

Ketose sugars


C

CH2OH

OHH

C O

H

C OHH

C

CH2OH

HOH

C O

H

C HOH

these two aldotetroses are enantiomers.They are stereoisomers that are mirrorimages of each other

C O

H

C HHO

C HHO

CH OH

C

CH2OH

OHH

C O

H

C HHO

C HHO

CHO H

C

CH2OH

OHH

these two aldohexoses are C-4 epimers.they differ only in the position of thehydroxyl group on one asymmetric carbon(carbon 4)

Enantiomers and epimers


Enantiomers

• Pairs of stereoisomers• Designated by D- or L- at the start of the

name. • They are mirror images

that can’t be overlapped.


Enantiomers


L- & D- glyceraldehyde

CHO

HO H

C

CH OH2

CH OH2

H

CHO

HO

CHO

H

C

CH OH2

OH

CH OH2

H

CHO

OH


CHO

HHO

OHH

CH2OH

CHO

OHH

OHH

CH2OH

aldotetroses

D-erythrose

D-threose

CHO

OHH

HHO

CH2OH

CHO

HHO

HHO

CH2OH

L-erythrose

L-threose

12

3

4

12

3

4

highest numbered "chiral" carbon




Aldotetrose


CHO

OHH

OHH

OHH

CH2OH

D-ribose

CHO

HHO

OHH

OHH

CH2OH

CHO

OHH

HHO

OHH

CH2OH

CHO

HHO

HHO

OHH

CH2OH

D-arabinose D-xylose D-lyxose

Aldopentoses: C5, three chiral carbons,

eight stereoisomers


Aldohexoses C6 four chiral carbons, sixteen

stereoisomers

D- glucose

CHO

OHH

OHH

OHH

OHH

CH2OH

CHO

HHO

OHH

OHH

OHH

CH2OH

CHO

OHH

HHO

OHH

OHH

CH2OH

CHO

HHO

HHO

OHH

OHH

CH2OH

D-allose D-altrose D-mannose

CHO

OHH

OHH

HHO

OHH

CH2OH

CHO

HHO

OHH

HHO

OHH

CH2OH

CHO

OHH

HHO

HHO

OHH

CH2OH

CHO

HHO

HHO

HHO

OHH

CH2OH

D-gulose D-idose D-galactose D-talose


CH2OH

O

HHO

OHH

OHH

CH2OH

D-fructose

CH2OH

O

CH2OH

dihydroxyacetone

CH2OH

O

OHH

OHH

CH2OH

D-ribulose

CH2OH

O

HO H

H OH

H OH

OHH

CH2OH

D-sedohepuloase

CH2OH

O

OHH

HHO

CH2OH

Dxylulose

Ketoses


Structural representation

of sugars• Fisher projection: straight chain

representation• Haworth projection: simple ring in

perspective• Conformational representation:

chair and boat configurations


Rules for drawing Haworth projections

• draw either a six or 5-membered ring including oxygen as one atom

• most aldohexoses are six-membered• aldotetroses, aldopentoses,

ketohexoses are 5-memberedO O



• next number the ring clockwise starting next to the oxygen

• if the substituent is to the right in the Fisher projection, it will be drawn down in the Haworth projection (Down-Right Rule)

O O

1

23

4

5

1

23

4



• for D-sugars the highest numbered carbon (furthest from the carbonyl) is drawn up. For L-sugars, it is drawn down

• for D-sugars, the OH group at the anomeric position is drawn down for aand up for β. For L-sugars a is up and β is down


D-glucose can cyclize in two ways forming either furanose or pyranose structures


CHO

OHH

HHO

OHH

HHOH2C

OH

D-glucose

OH

HOHH

HO

O

CHO

OH

H

H

OHH

OH

HOH2C

H

HO

H

OH H

CH2OH

H

OH

OOHH

HO

HH

OH H

CH2OH

HOH

HO

H

OHH

OHH

OH

CH2OH

H

OH

HO

OH

HH

OHH

OH

CH2OH

H

new chiral center

1

3

4

5

6

1 1

11

2

2

2 2

1

3

33 2

3

3

4

4

4 4

4

5

5

5

55

6

6

6

6

6

Pyranose Forms


Glucose exists in aqueous solution primarily in the six-membered, pyranose ring form

• Results from intramolecular nucleophilic addition of the –OH group at C5 to the C1 carbonyl group

Cyclic Structures of Monosaccharides:


• The name pyranose is derived from pyranPyran is the name of the unsaturated six-

membered cyclic ether• Pyranose rings have chairlike geometry with axial

and equatorial substituents

Cyclic Structures of Monosaccharides:


AnomersThe two diastereomers are called anomers and the hemiacetal carbon atom is referred to as the anomeric center


D-ribose and other five-carbonsaccharides can form eitherfuranose or pyranose structures


CHO

OHH

OHH

OHH

HH

OH

D-ribose

OH

HOHHO

HO

O

CHO

OH

H

OH

HH

OH

H

H

HO

H

H H

H

H

OH

OOHHO

HO

HH

H H

H

HOH

HO

H

OHH

OHOH

H

H

H

OH

HO

OH

HH

OHOH

H

H

H

new chiral center

1

3

4

5

1 1

11

2

2

2 2

1

3

33 2

3

3

4

4

4 4

4

5

5

5

55

Pyranose Forms


CH2OH

O

HHO

OHH

HHOH2C

OH

1

4

2

3

5

6

CH2OH

O

HHO

OHH

OHH

CH2OH

1

4

2

3

5

6

CH2OH

OH

OHH

OH

HOH2C

H

HO2

1345

6

H

HOH2C

OH H

H HOOH

CH2OH

O

1

2345

6

CH2OH

OH

H

CH2OH

OH H

H HOO

CH2OH

OH

OHH

OH

H

OH

HOH2C2

1345

6

OH

CH2OHHHO

HO

OH

H HO

H

HOH

HO

OH

CH2OH

HO

HOH

H

H

H

6

2

334

45

56

1 1

1

2

34

5

6

2

Fructofuranose and Fructopyranose


Chair and boat conformations of a pyranose sugar

2 possible chair conformationsof b-D-glucose


Optical isomerism

• A property exhibited by any compound whose mirror images are non-superimposable

• Asymmetric compounds rotate plane polarized light


POLARIMETRYMeasurement of optical activity in chiral or

asymmetric molecules using plane polarized light

Molecules may be chiral because of certain atoms

or because of chiral axes or chiral planes

Measurement uses an instrument called a

polarimeter (Lippich type)

Rotation is either (+) dextrorotatory or (-)

levorotatory


POLARIMETER


New polarimeters usually connected to computer

and printer


polarimetry

Magnitude of rotation depends upon:

Nature of the compound

Length of the tube usually expressed in decimeters

Wavelength of the light source employed

Temperature of sample

Concentration of analyte in grams per 100 ml


Specific rotation of carbohydrates

• D-glucose +52.7 D-fructose -92.4• D-galactose +80.2 L-arabinose +104.5• D-mannose +14.2 D-arabinose -105.0• D-xylose +18.8 Lactose +55.4• Sucrose +66.5 Maltose

+130.4• Invert sugar -19.8 Dextrin +195


Reactions of monosaccharides

• Carbonyl reactions:•Osazone formation•Reduction , Oxidation•Amino Sugars


Formation of osazone

• consists of reacting the monosaccharide with phenylhydrazine

• D-fructose and D-mannose give the same osazone as D-glucose

• seldom used for identification; we now use HPLC or mass spectrometry


OSAZONESThe aldehyde group of an aldose react with phenylhydrazine.

O

CH

(CHOH)n

CH2OH

H

C NNHC6H5

C

(CHOH)n

CH2OH

+ 3C6H5NHNH2 NNHC6H5+ C6H5NH2 + NH3 + H2O

phenylosazone (±½ëÛ)


Oxidation reactions

• Aldoses may be oxidized to 3 types of acidsAldonic acids: aldehyde group is converted

to a carboxyl group Uronic acids: aldehyde is left intact and

primary alcohol at the other end is oxidized to COOH

Saccharic acids (glycaric acids) – oxidation at both ends of monosaccharide)


• Br2 is a mild oxidant that gives good yields of aldonic acid products

Oxidation


• Aldoses are oxidized in warm, dilute HNO3 to dicarboxylic acids called aldaric acids

Oxidation


• Enzymatic oxidation at the –CH2OH end of aldoses yields uronic acids

Oxidation


Reduction

• either done catalytically or enzymatically• Forms sugar alcohol (alditol)• glucose form sorbitol (glucitol)• mannose forms mannitol• fructose forms a mixture of mannitol and

sorbitol• glyceraldehyde gives glycerol


Aldoses( and ketoses) can be reduced with sodium borohydride

NaBH4

OHO

HOH2C

HO

OH

HO

CHO

H OH

HO H

H OH

H OH

CH2OH

CH2OH

H OH

HO H

H OH

H OH

CH2OH

D-GlucoseD-Glucitol (D-ÆÏÌÑÌÇ´¼£©

Reduction


Sugar alcohols


Deoxy Sugars

• These are monosaccharides which lack one or more hydroxyl groups on the molecule

• one quite ubiquitous deoxy sugar is 2’-deoxy ribose which is the sugar found in DNA

• 6-deoxy-L-mannose (L-rhamnose) is used as a fermentative reagent in bacteriology


examples of deoxysugars


Several sugar esters importantin metabolism


Amino Sugars


Glycosides


Oligosaccharides

• Most common are the disaccharides• Sucrose, lactose, and maltose• Maltose hydrolyzes to 2 molecules of D-

glucose• Lactose hydrolyzes to a molecule of glucose

and a molecule of galactose• Sucrose hydrolyzes to a moledule of glucose

and a molecule of fructose


β - Maltose• Malt sugar. Not common in nature except in

germinating grains. α (1 4) linkage.

-D-glucose -D-glucose

OH

OH

H

H

H

OH

CH 2 OH

H

OH

OH OH

H

H

H

OH

CH 2 OH

H

OH

O


Lactose

• Milk sugar - dimer of -D-galactose and or - D-glucose. (1 4)

OOH

H H

H

H

OH

CH 2 OH

H

OH

OH OH

H

H

H

OH

CH 2 OH

H

OH

O

-D-galactose -D-glucose


Sucrose

• Table sugar - most common sugar in all plants.

• Sugar cane and beet, are up to 20% by mass sucrose.

• Disaccharide of -glucose and -fructose.(1 2) linkage

CH2OH O

CH2OHH

OH H

H OH

H O

OH

H

H

OHH

OH

CH2OH

H

O


Polysaccharides or glycans

• homoglycans (starch, cellulose, glycogen, inulin)

• heteroglycans (gums, mucopolysaccharides)


Starch

• most common storage polysaccharide in plants

• composed of 10 – 30% -a amylose and 70-90% amylopectin depending on the source

• the chains are of varying length, having molecular weights from several thousands to half a million


Amylopectin starch• Branched structure due to crosslinks.

β(1 6) link age at crosslink

OHH OHH OHH

OH H

HOH

CH2OH

H

OH H

HOH

CH2OH

H

O O

OH H

HOH

CH2OH

H

OH H

H

OHH

OH

CH2OH

H

O O

OH H

H

OHH

OH

CH2OH

H

OH H

H

OHH

OH

CH2OH

H

O O

OH H

H

OHH

OH

CH2OH

H

OH H

H

OHH

OH

CH2

H

O O


Starch• Main sources of starch are rice, corn,

wheat, potatoes and cassava• Starch is used as an excipient, a binder in

medications to aid the formation of tablets.

• Industrially it has many applications such as adhesives, paper making, biofuel, textiles


c

Glycogen

• Energy storage of animals.• Stored in liver and muscles as granules.• Similar to amylopectin. α(1 6) linkage

OO

O

OO

O

O

O

O

O

O

O

O

O

c


Amylose and amylopectin are the 2 forms of starch. Amylopectinis a highly branched structure, with branches occurring every 12to 30 residues


H OO

HH

OHH

COO-

HO

H O

OH

O

HH

NH

CH2OH

H

C OCH3

H OO

HH

OHH

COO-

HO

H O

OH HH

NH

CH2OH

H

C OCH3

H OO

HH

OHH

COO-

HO

H O

OH

O

HH

NH

CH2OH

H

C OCH3O

Mucopolysaccharides

• These materials provide a thin, viscous, jelly-like coating to cells. The most abundant form is hyaluronic acid.

•

Alternating units of N-acetylglucosamine and

• D-glucuronic acid.

(1 3)

(1 4)


Peptidoglycans• Bacterial cell walls are composed primarily of an

unbranched polymer of alternating units of N-acetylglucosamine and N-acetylmuramic acid.

• Peptide crosslinks between the polymer strands provide extra strength varies based on bacterium.

H O

O H

H

NHH

OH

CH2OH

H

C

CH3

O

H O O

H

H

NHH

OR

CH2OH

H

C

CH3

O

O


REFERENCES

John E McMurry : Organic ChemistryGarrett & Grisham: Textbook of BiochemistryLehninger: Fundamentals of BiochemistryMorris Hein, Scott Pattison, and Susan Arena:Introduction to Biochemistry


The End

Carbohydrates

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