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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-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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