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CarbohydratesCarbohydrates
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Dr Vivek Joshi
Contents and Learning Contents and Learning ObjectivesObjectives Introduction Functions General classification Various representation Monosaccharide structure and isomerism Disaccharides- Sucrose, Lactose & Maltose Polysaccharides- Starch, Glycogen Acidic Polysaccharides: biological importance
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IntroductionIntroduction Proximate principle of the diet-Carbohydrate, Lipid, Protein
Carbohydrate:◦ Energy: 4 kcal/gm◦ 60-70% of energy◦ Preferred fuel◦ Brain and RBC are wholly dependent on Glucose for their energy
needs Lipid:
◦ Energy: 9 kcal/gm◦ Concentrated fuel substance
Protein:◦ Tissue building material◦ Many special functions- enzymes, antibodies, carrier molecules etc.
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Functions of Functions of CarbohydratesCarbohydratesSource and storage of energyIn structure of connective tissueSynthesis of biologically important
compounds like: Ribose and Deoxyribose in Nucleic acid Glycoprotein in Hormones, Blood group substances Glycolipid in Nervous tissue Proteoglycan in mucous secretion Glucuronic acid in detoxification
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Carbohydrates: Definition & Carbohydrates: Definition & NameName“Polyhydroxylated aldehyde and ketone derivatives or compounds that gives these compounds on hydrolysis” “hydrate of carbon” Empiric formula: Cn(H2O)m
Saccharide: simpler members of carbohydrate family (saccharum=sugar, for sweet taste) Suffix: ‘-ose’ Prefix: tri-, tetr-, pent-, hex- etc. indicates number of carbon atoms Carbohydrates
Containing aldehyde group= aldosesContaining ketone group= ketoses
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Carbohydrates Carbohydrates ClassificationClassification
Monosaccharide [One sugar unit-CnH2nOn or Cn(H2O)n] Triose (3C) Tetrose (4C) Pentose (5C) Hexose (6C) Heptose (7C)
Disaccharide [Two sugar units-Cn(H2O )(n-1) ] Sucrose (Glucose and Fructose) Maltose (Glucose and Glucose) Lactose (Glucose and Galactose)
Oligosaccharide [3-10 sugar units] Stacchyrose, Raffinose
Polysaccharide [>10 sugar units] Starch Glycogen Cellulose Hyaluronic acid Heparin
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Aldoses: Aldoses: MonosaccharidesMonosaccharides
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Ketoses: Ketoses: MonosaccharidesMonosaccharides
Various RepresentationVarious Representation Fischer Projection Formulas:
◦ A two dimensional representation showing the configuration of a stereocenter;
◦ Horizontal lines represent bonds projecting forward
◦ Vertical lines represent bonds projecting toward the back
◦ D and L varieties
Cyclic Structure:◦ Pyran: six membered ring◦ Furan: five membered ring
Haworth Projection:◦ A flat ring as is viewed through its edge◦ α and β varieties
Conformational Representation:◦ Chair
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Monosaccharide Structure Monosaccharide Structure and Isomerismand IsomerismTypes of isomerism
1. Functional isomerism: Aldose & Ketose
2. Stereoisomerism: D and L
3. Anomerism: and
4. Optical Isomerism: d(+) and l(-)
5. Epimerism
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1. Functional isomerism1. Functional isomerism Exhibited by the monosaccharides having the same molecular
formula but different functional groups Sugar with Aldehyde group- Aldose sugar Sugar with Keto group- Ketose sugar
Monosaccharides are subclassified as:Aldose Ketose
Triose (3C) Glyceraldehyde Dihdroxy acetone Tetrose (4C) Erythrose Erythrulose Pentose (5C) Ribose Ribulose Hexose (6C) Glucose Fructose Heptose (7C) Heptose Sedoheptulose
11Pentoses and hexoses are the most abundant monosaccharides in living cells
2. Streioisomerism2. Streioisomerism Exhibited by the monosaccharides having the same molecular
formula but differ in the arrangement of H and OH group around penultimate (last but one) carbon atom
Asymmetric/Chiral carbon which is farthest from the functional group.
D-sugar: -OH group on penultimate carbon atom is on the right L-sugar: -OH group on penultimate carbon atom is on the left
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2. Streioisomerism (contd.)2. Streioisomerism (contd.)
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D-Sugar: • Naturally occurring• Normally metabolized in the body.
L-Sugar:• Occur rarely• Normally NOT metabolized in the body.• Present in toxins, poison and Antibiotics
3. Anomerism3. Anomerism Exhibited by the sugars having the
same molecular formula but differ in the arrangement of H and OH group around anomeric carbon atom
Anomeric carbon: due to cyclization, carbonyl carbon becomes new chiral center
[To remember, C bonded with functional group is anomeric carbon]
Anomeric carbon atom◦ Involved in hemiacetal ring formation in Aldose◦ Involved in hemiketal ring formation in Ketose◦ C1 in Glucose◦ C2 in Fructose
Anomer: -OH on the Right Anomer :-OH on the Left
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Note: Acetal is a molecule with two single bonded oxygens attached to the same carbon
3. Anomerism (contd.)3. Anomerism (contd.)
Sugars that contain ≥ 4 carbons exist primarily in cyclic forms in aqueous solutions.
Pyranose = 6-membered ring
Furanose = 5-membered ring
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3. Anomerism (contd.)3. Anomerism (contd.)
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Glucose
C1 of Glucose forms hemiacetal ring with C5
Fischer projectionOH on the right at C1 - OH on the left at C1-
Haworth projectionOH below the plane at C1 - OH above the plane at C1 -
3. Anomerism (contd.)3. Anomerism (contd.)
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FructoseC2 of Fructose forms hemiketal ring with C5
Fischer projectionOH on the right at C2 - OH on the left at C2 -
Haworth projectionOH below the plane at C2 - OH above the plane at C2 -
3. Anomerism (contd.)3. Anomerism (contd.)
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Glucose in solution - more than 99% is in the pyranose form
β-D-Glucopyranose (62%) is the most predominant
form of Glucose in blood.
3. Anomerism (contd.)3. Anomerism (contd.)
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Fructose in solution – primarily in the furanose form
4. Optical Isomerism4. Optical Isomerism Exhibited by the sugars having the same molecular formula but differ in optical
activity
Beam of plane polarized light is made to pass through the solution of a compound◦ dextrorotatory – d(+): Light rotated towards clockwise◦ levorotatory – l(-): Light rotated towards anticlockwise
Racemic mixture: Equimolar concentration of optical isomers◦ No net optical rotation
The specific rotation, []D: Optical rotation expression under standard conditions◦ The observed rotation when light of 589.6 nanometer* (nm; 1 nm = 10-9 m) wavelength is used with a sample pathlength l of 10 cm and a sample concentration C of 1 g/mL
*Light of 589.6 nm, sodium D line, is the orange light emitted from common sodium lamps
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5. Epimerism5. Epimerism Exhibited by the sugars having the same molecular formula but
differ in the arrangement of H and OH group around a single asymmetric carbon atom other than anomeric carbon atom
Glucose and Galactose are epimers at C4 Glucose and Mannose are epimers at C2 Epimerase enzyme: interconverts these epimers
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Glycosidic bondGlycosidic bond In Di, Oligo and Polysaccharides: Sugar units linked by
glycosidic linkage Glycosidic bond/linkage is formed by the condensation
of the –OH group of the anomeric carbon of one sugar and an –OH group at any position on another sugar
Common Glycosidic linkage-Between C1 of the first sugar and the –OH at C4 of the second sugar (1 → 4 linkage)
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DisaccharidesDisaccharides
A carbohydrate containing two monosaccharides units joined together by glycosidic bond
◦Sucrose ◦Lactose◦Maltose
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SucroseSucrose Glucose + Fructose Table sugar, Present in Fruits and Honey Also from cane Sugar (sugarcane) and beet sugar 1,2-glycosidic bond
Non reducing sugar: because both anomeric carbons (C1 of glucose and C2 of fructose) are involved in glycosidic bond and not free to react
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O
HOOH
OH
CH2OH
O
OH
HOO
CH2OH
HOCH2
OHO
HO
OOH
CH2OH
OH
HOO
CH2OH
HOCH2
1
1
2
1
2
1
a unit of -D-glucopyranose
a unit of -D-fructofuranose
-1,2-glycosidic bond
LactoseLactose Galactose + Glucose Milk sugar -1,4 glycosidic bond between C1 of Galactose and C4 of
Glucose
Reducing sugar: as the functional group (-CHO on C1) of 2nd glucose is not involved in glycosidic bond and free to react, i.e. can be oxidized
Also note bonds in comparison to bonds bonds oriented above the plane of ring (as in anomers)
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OOH
HOOH
O
CH2OH
OHO
OH OH
CH2OHOOH O
OH
OH
CH2OHO OH
OH
OH
CH2OH
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4
4
-1,4-glycosidic bond
MaltoseMaltose Glucose + Glucose Malt sugar -1,4 glycosidic bond Reducing sugar : as the functional group (-CHO on C1)
of 2nd glucose is not involved in glycosidic bond and free to react, i.e. can be oxidized
Also note bonds below the plane of ring
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OHOHO OH OOHO OH
OH
CH2OH
CH2OHO
OH
OOHHO
O OH
HO
OHCH2OH
HOCH2 14
-1,4-glycosidicbond1 4
Disaccharides: Must Remember!Disaccharides: Must Remember!
Common Name
Monomers Bonding Reduction?
Sucrose
Table sugar
Glucose + Fructose
1,2-glycosidic bond
Non-reducing
Lactose
Milk sugar
Galactose + Glucose
-1,4- glycosidic bond
Reducing
Maltose
Malt sugar
Glucose + Glucose
-1,4- glycosidic bond
Reducing
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PolysaccharidesPolysaccharides“a carbohydrate consisting of large
numbers of monosaccharide units joined by glycosidic bonds”
A. StarchB. GlycogenC. Cellulose
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StarchStarch Storage form of carbohydrate in plants Found in potatoes, corn, and cereal grains Polymer of only D-glucose Has two components1. Amylose (20-25%): Continuous, un-branched chain of around 4,000 D-glucose
units D-glucose residues - linked with -1,4-glycosidic bonds
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Starch (contd.)Starch (contd.) 2. Amylopectin (75-80%): ◦ Branched chains◦ Around 10,000 Glucose residues united by -1,4 linkages◦ Branching point after every 24-30 Glucose units with -1,6-
linkages
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GlycogenGlycogen Storage form of carbohydrate in Animals Stored in the liver and muscle
Polymer of around 106 glucose units Glycosidic bonds are similar to amylopectin, but has more
branches Branches after every 8-10 glucose units Total amount in human body = 500-600 grams
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All the bonds: Must Remember!All the bonds: Must Remember!
Di/Polysaccharide BondsSucrose Di 1,2-glycosidic bondLactose Di -1,4 glycosidic bondMaltose Di -1,4 glycosidic bondStarch: (a) Amylose Poly only -1,4-glycosidic bonds (b) Amylopectin -1,4-glycosidic bonds
with -1,6- linkages at branches
Glycogen Poly -1,4-glycosidic bondswith -1,6- linkages at branches
Cellulose Poly β-1, 4- glycosidic bonds
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Acidic PolysaccharidesAcidic Polysaccharides“a group of polysaccharides that contain carboxyl
groups and/or sulfuric ester groups, and play important roles in the structure and function of connective tissues”.
Now being called Glycosaminoglycans There is no single general type of connective tissue. Rather, there are a large number of highly specialized
forms, such as cartilage, bone, synovial fluid, skin, tendons, blood vessels, intervertebral disks, and cornea.
Most connective tissues are made up of collagen, a structural protein, in combination with a variety of acidic polysaccharides.
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Hyaluronic acid Hyaluronic acid Simplest acid polysaccharide Contains from 300 to 100,000 repeating units.
It is most abundant in embryonic tissues and in specialized connective tissues such as ◦ the synovial fluid, the lubricant of joints in the body, and ◦ the vitreous of the eye where it provides a clear, elastic gel
that maintains the retina in its proper position.
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OHO
OH
COO-OHO
NH
CH2OH
CH3C O
O O
The repeating unit of hyaluronic acid
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D-glucuronic acid N-Acetyl-D-glucosamine
Thank You
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