Lect 1 Sucrose [Compatibility Mode]

8/3/2019 Lect 1 Sucrose [Compatibility Mode]

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PHARM. D

Chemical Pharmacognosy- I

Lecture 1February 17, 2011

CARBOHYDRATESSUCROSE

M.M. AhsanAhsan KhalidKhalid,, B.PharmB.Pharm, Pharm. D, Pharm. DM.PhilM.Phil Scholar (RIPS/RIU)Scholar (RIPS/RIU)

HIPSHIPS--HUKICHUKIC


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Monosaccharides - simple sugars with multiple OH groups.

Based on number of carbons (3, 4, 5, 6), a monosaccharide

is a triose, tetrose, pentose or hexose.

Disaccharides - 2 monosaccharides covalently linked.

Oligosaccharides - a few monosaccharides covalently

linked.

Polysaccharides - polymers consisting of chains of

monosaccharide or disaccharide units.

I

(CH2O)n or H-C-OHI

Carbohydrates (glycans) have the followingbasic composition:

There are a variety of interrelated classification schemes. The most

useful classification scheme divides the carbohydrates into groups

according to the number of individual simple sugar units.


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Monosaccharides

Aldoses (e.g., glucose) have

an aldehyde group at one end.

Ketoses (e.g., fructose) have

a keto group, usually at C2.

C

C OHH

C HHO

C OHH

C OHH

CH2OH

D-glucose

OH

C HHO

C OHH

C OHH

CH2OH

CH2OH

C O

D-fructose


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Monosaccharides

Glucose

From Greek word for sweet wine; grape

sugar, blood sugar, dextrose.

Galactose

Greek word for milk--"galact", found as a

component of lactose in milk.

Fructose

Latin word for fruit--"fructus", also known as

levulose,

found in fruits and honey; sweetest sugar.

Ribose

Ribose and Deoxyribose are found in the

backbone structure of RNA and DNA,

respectively.


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Hemiacetal & hemiketal formation

An aldehyde can

react with analcohol to form

a hemiacetal.

A ketone canreact with an

alcohol to form

a hemiketal.

O C

H

R

OH

O C

R

R'

OHC

R

R'

O

aldehyde alcohol hemiacetal

ketone alcohol hemiketal

C

H

R

O R'R' OH

"R OH "R

+

+


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Cellobiose, a product of cellulose breakdown, is the

otherwise equivalent b anomer (O on C1 points up).The b(1 4) glycosidic linkage is represented as a zig-zag,but one glucose is actually flipped over relative to the other.

H O

OH

H

OHH

OH

CH2OH

H

O H

OH

H

OHH

OH

CH2OH

H

O

HH

1

23

5

4

6

1

23

4

5

6

maltose

H O

OH

H

OHH

OH

CH2OH

H

O OH

H

H

OHH

OH

CH2OH

H

H

H

O1

23

4

5

6

1

23

4

5

6

cellobiose

Disaccharides:

Maltose, a cleavageproduct of starch

(e.g., amylose), is adisaccharide with an

a(1 4) glycosidic

link between C1 - C4OH of 2 glucoses.

It is the a anomer(C1 O points down).


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Otherdisaccharides

include: Sucrose, common table sugar, has a glycosidic bond

linking the anomeric hydroxyls ofglucose & fructose.

Because the configuration at the anomeric C of glucose

is a (O points down from ring), the linkage is a(12).

The full name of sucrose is a-D-glucopyranosyl-(12)-

b-D-fructopyranose.)

Lactose, milk sugar, is composed ofgalactose &glucose, with b(14) linkage from the anomeric OH of

galactose. Its full name is b-D-galactopyranosyl-(1 4)-

a-D-glucopyranose


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Disaccharides - contain two monosaccharides

Sucrose

French word for sugar--"sucre", a disaccharide

containing glucose and fructose; table sugar, cane

sugar, beet sugar.

Lactose

Latin word for milk--"lact"; a disaccharide found in

milk containing glucose and galactose.

Maltose

French word for "malt"; a disaccharide containing

two units of glucose; found in germinating grains,

used to make beer.


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Polysaccharides:

Plants store glucose as amylose or amylopectin, glucosepolymers collectively called starch.

Glucose storage in polymeric form minimizes osmotic

effects.

Amylose is a glucose polymer with a(14) linkages.The end of the polysaccharide with an anomeric C1 not

involved in a glycosidic bond is called the reducing end.

H O

OH

H

OHH

OH

CH2OH

H

O H

H

OHH

OH

CH2OH

H

O

HH H O

O

H

OHH

OH

CH2OH

HH H

O

H

OHH

OH

CH2OH

H

OH

HH O

O

H

OHH

OH

CH2OH

H

O

H

1

6

5

4

3

1

2

amylose


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Amylopectin is a glucose polymer with mainly a(14)

linkages, but it also has branches formed by a(16)

linkages. Branches are generally longer than shown above.

The branches produce a compact structure & provide

multiple chain ends at which enzymatic cleavage can occur.

H O

OH

H

OHH

OH

CH2OH

H

O H

H

OHH

OH

CH2OH

H

O

HH H O

OH

OHH

OH

CH2

HH H O

H

OHH

OH

CH2OH

H

OH

HH O

OH

OHH

OH

CH2OH

H

O

H

O

1 4

6

H O

H

OHH

OH

CH2OH

H

H H O

H

OHH

OH

CH2OH

H

H

O

1

OH

3

4

5

2

amylopectin


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Glycogen, the glucose storage polymer in animals, issimilar in structure to amylopectin.

But glycogen has more a(16) branches.

The highly branched structure permits rapid glucose releasefrom glycogen stores, e.g., in muscle during exercise.

The ability to rapidly mobilize glucose is more essential toanimals than to plants.

H O

OH

H

OHH

OH

CH2OH

H

O H

H

OHH

OH

CH2OH

H

O

HH H O

OH

OHH

OH

CH2

HH H O

H

OHH

OH

CH2OH

H

OH

HH O

OH

OHH

OH

CH2OH

H

O

H

O

1 4

6

H O

H

OHH

OH

CH2OH

HH H O

H

OHH

OH

CH2OH

HH

O

1

OH

3

4

5

2

glycogen


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Cellulose, a major constituent ofplant cell walls, consists

of long linear chains of glucose with b(14) linkages.

Every other glucose is flipped over, due to b linkages.This promotes intra-chain and inter-chain H-bonds and

cellulose

H O

OH

H

OHH

OH

CH2OH

H

O

H

OHH

OH

CH2OH

HO

H H O

O H

OHH

OH

CH2OH

H

H O

H

OHH

OH

CH2OH

H

H

OHH O

O H

OHH

OH

CH2OH

HO

H H H H

1

6

5

4

3

1

2

van der Waals interactions,that cause cellulose chains to

be straight & rigid, and packwith a crystalline arrangement

in thick bundles - microfibrils.

See: Botany online website;website at Georgia Tech.

Schematic of arrangement of

cellulose chains in a microfibril.


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Multisubunit Cellulose Synthase complexes in the plasma

membrane spin out from the cell surface microfibrilsconsisting of 36 parallel, interacting cellulose chains.

These microfibrils are very strong.

The role of cellulose is to impart strength and rigidity to

plant cell walls, which can withstand high hydrostatic

pressure gradients. Osmotic swelling is prevented.

Explore and compare structures of amylose & cellulose

using Chime.

cellulose

H O

OH

H

OHH

OH

CH2OH

H

O

H

OHH

OH

CH2OH

HO

H H O

O H

OHH

OH

CH2OH

H

H O

H

OHH

OH

CH2OH

H

H

OHH O

O H

OHH

OH

CH2OH

HO

H H H H

1

6

5

4

3

1

2


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Common Polysaccharides

Name Source

Starch

Plants store glucose as the polysaccharide starch. The cereal grains

(wheat, rice, corn, oats, barley) as well as tubers such as potatoes

are rich in starch.

Cellulose

The major component in the rigid cell walls in plants is cellulose

and is a linear polysaccharide polymer with many glucose

monosaccharide units.

Glycogen

This is the storage form of glucose in animals and humans which

is analogous to the starch in plants. Glycogen is synthesized and

stored mainly in the liver and the muscles.


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Sucrose is made from glucose and fructose units:

Sucrose or table sugar is obtained from sugar caneor sugar beets.

The glucose and fructose units are joined by an

acetal oxygen bridge in the alpha orientation.


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Invert Sugar:

When sucrose is hydrolyzed it forms a 1:1 mixtureof glucose and fructose. This mixture is the main

ingredient in honey.

It is called invert sugar because the angle of thespecific rotation of the plain polarized light

changes from a positive to a negative value due to

the presence of the optical isomers of the mixture

of glucose and fructose sugars.


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Hydrolysis of Sucrose:

In the hydrolysis of any di- or polysaccharide, a water

molecule helps to break the acetal bond.

The acetal bond is broken, the H from the water is added

to the oxygen on the glucose.

The -OH is then added to the carbon on the fructose.


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Synthesis and Biosynthesis of Sucrose

The biosynthesis of sucrose proceeds via the precursors UDP-glucoseand fructose 6-phosphate, catalyzed by the enzyme sucrose-6-

phosphate synthase.

The energy for the reaction is gained by the cleavage of Uridine

diphosphate (UDP).

Sucrose is formed by plants but not by other organisms. Sucrose is

found naturally in many food plants along with the monosaccharide

fructose.

In many fruits, such as pineapple and apricot, sucrose is the main

sugar. In others, such as grapes and pears, fructose is the main sugar.


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The prodution of sucrose takes place in plants, to store energy

produced during photosynthesis. The extraction of sucrose from

plants like sugar cane and sugar beets is used to produce sugar for

consumption, making this pathway of significant economic interest.

The starting point for sucrose synthesis is activated glucose, UDP-

glucose. UDP-glucose used in sucrose synthesis is derived from

glucose-1-phosphate, which is itself derived from photosyntheticproducts.

The fructose-6-phosphate involved in sucrose synthesis is also

derived from photosynthetic products. The enzyme sucrose 6-

phosphate synthase is regulated in several ways.

Glucose-6-phosphate activates this enzyme, and

dephosphorylation of this enzyme in light also activates sucrose 6-

phosphate synthase, coordinating sucrose synthesis with

photosynthesis.


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PRODUCTIONSugar or more specifically sucrose is a carbohydrate that

occurs naturally in every fruit and vegetable.

It is the major product of photosynthesis, the process by which

plants transform the sun's energy into food.

Sugar occurs in greatest quantities in sugar cane and sugar

beets from which it is separated for commercial use.


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In the first stage of processing the natural sugar stored in the cane stalk

or beet root is separated from the rest of the plant material by physicalmethods.

For Sugar Cane, this is accomplished by:

a) pressing the cane to extract the juice containing the sugar

b) boiling the juice until it begins to thicken and sugar begins tocrystallize

c) spinning the sugar crystals in a centrifuge to remove the syrup,

producing raw sugar; the raw sugar still contains many impurities

d) shipping the raw sugar to a refinery where it is washed and filtered

to remove remaining non-sugar ingredients and color

e) crystallizing, drying and packaging the refined sugar.


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Beet sugar processing is similar, but it is done

in one continuous process without the raw sugar

stage.

The sugar beets are washed, sliced and soaked

in hot water to separate the sugar-containing

juice from the beet fiber.

The sugar-laden juice is purified, filtered,concentrated and dried in a series of steps

similar to cane sugar processing.


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The production of sugarcane needs approximately four times as much

water as the production of sugar beet,

On the other hand, sugar cane tolerates hot climates better.

The production of sugar results in residues that differ substantiallydepending on the raw materials used and on the place of production.

While cooks often use cane molasses in food preparation, humans find

molasses from sugar beet unpalatable, and it, therefore, ends up mostlyas industrial fermentation feedstock (for example in alcohol distilleries),

or as animal feed.

Once dried, either type of molasses can serve as fuel for burning.

CANE VERSUS BEET


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Health Hazards

Tooth Decay

Glycemic Index Diabetes

Gout


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Tooth Decay the most prominent health hazard associated

with the consumption of sugar

Oral bacteria such as Streptococcus mutans

live in dental plaque and metabolize anysugars (not just sucrose, but also glucose,

lactose, fructose, or cooked starches) into

lactic acid.

High concentrations of acid may result on

the surface of a tooth, leading to tooth

demineralization


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Glycemic Index

Sucrose has a moderately high glycemic index (64,about the same as honey, 62, but not nearly that of

maltose, 105), which, in turn, causes an immediate

response within the body's digestive system

Like other sugars, sucrose is digested into glucose

(blood sugar) and transported into the blood

overconsumption may cause an increase in blood

sugar levels from a normal 90 mg/dL to up over

150 mg/dL.


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Diabetes

Type 1 diabetes & Type 2 diabetes

Glucose build up in the bloodstream can cause two

problems: in the short term, cells become starved for energy

because they do not have access to the glucose

in the long term, frequent glucose build-up increases

the acidity of the blood, damaging many of the

body's organs, including the eyes, kidneys, nerves

and/or heart


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Gout

The occurrence ofgout is connected with an excess

production of uric acid.

A diet rich in sucrose may lead to gout as it raises the

level of insulin, which prevents excretion of uric

acid from the body.As the concentration of uric acid in the body increases,

so does the concentration of uric acid in the joint

liquid and beyond a critical concentration, the uricacid begins to precipitate into crystals.

Researchers have implicated sugary drinks high in

fructose in a surge in cases of gout

Lect 1 Sucrose [Compatibility Mode]

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