Home Science Carbohydrates CARBOHYDRATES Dr. Daxaben N. Mehta Principal Smt. Sadguna C.U.Shah Home Science and U. Shah Arts & Commerce Mahila Colleg Wadhwancity, Dist: Surendranagar
May 11, 2015
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
Home Science Carbohydrates
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)
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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
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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
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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
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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…)
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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
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Structure of aldose and ketose
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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
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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
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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
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Enantiomers
• Pairs of stereoisomers• Designated by D- or L- at the start of the
name. • They are mirror images
that can’t be overlapped.
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Enantiomers
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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
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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
highest numbered "chiral" carbon
highest numbered "chiral" carbon
highest numbered "chiral" carbon
Aldotetrose
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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
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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
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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
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Structural representation
of sugars• Fisher projection: straight chain
representation• Haworth projection: simple ring in
perspective• Conformational representation:
chair and boat configurations
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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
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Rules for drawing Haworth projections
• 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
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Rules for drawing Haworth projections
• 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
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D-glucose can cyclize in two ways forming either furanose or pyranose structures
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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
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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:
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• 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:
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AnomersThe two diastereomers are called anomers and the hemiacetal carbon atom is referred to as the anomeric center
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D-ribose and other five-carbonsaccharides can form eitherfuranose or pyranose structures
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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
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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
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Chair and boat conformations of a pyranose sugar
2 possible chair conformationsof b-D-glucose
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Optical isomerism
• A property exhibited by any compound whose mirror images are non-superimposable
• Asymmetric compounds rotate plane polarized light
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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
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POLARIMETER
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New polarimeters usually connected to computer
and printer
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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
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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
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Reactions of monosaccharides
• Carbonyl reactions:•Osazone formation•Reduction , Oxidation•Amino Sugars
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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
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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)
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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)
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• Br2 is a mild oxidant that gives good yields of aldonic acid products
Oxidation
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• Aldoses are oxidized in warm, dilute HNO3 to dicarboxylic acids called aldaric acids
Oxidation
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• Enzymatic oxidation at the –CH2OH end of aldoses yields uronic acids
Oxidation
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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
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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
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Sugar alcohols
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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
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examples of deoxysugars
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Several sugar esters importantin metabolism
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Amino Sugars
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Glycosides
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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
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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
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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
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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
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Polysaccharides or glycans
• homoglycans (starch, cellulose, glycogen, inulin)
• heteroglycans (gums, mucopolysaccharides)
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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
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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
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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
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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
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Amylose and amylopectin are the 2 forms of starch. Amylopectinis a highly branched structure, with branches occurring every 12to 30 residues
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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)
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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
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REFERENCES
John E McMurry : Organic ChemistryGarrett & Grisham: Textbook of BiochemistryLehninger: Fundamentals of BiochemistryMorris Hein, Scott Pattison, and Susan Arena:Introduction to Biochemistry
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The End