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Chemistry 20. Chapter 12 Carbohydrates. Carbohydrates. Produced by photosynthesis in plants. The major source of energy from our diet. Composed of the elements C, H, and O. C n (H 2 O) n. Photosynthesis. 6CO 2 + 6H 2 O + energyC 6 H 12 O 6 + 6O 2. Respiration. glucose.

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Chapter 12 Carbohydrates

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Chapter 12 carbohydrates

Chemistry 20

Chapter 12

Carbohydrates


Chapter 12 carbohydrates

Carbohydrates

  • Produced by photosynthesis in plants.

  • The major source of energy from our diet.

  • Composed of the elements C, H, and O.

Cn(H2O)n

Photosynthesis

6CO2 + 6H2O + energyC6H12O6 + 6O2

Respiration

glucose


Chapter 12 carbohydrates

Carbohydrates

  • The most abundant organic compounds in the plant world.

  • 3/4 of the weight of plants.

  • 1% of the weight of animals and humans (they do not store).

  • 65% of the foods in our diet.


Chapter 12 carbohydrates

Carbohydrates

H+ or enzyme

1. Monosaccharide + H2Ono hydrolysis

H+ or enzyme

2. Disaccharide + H2Otwo monosaccharide units

+

H+ or enzyme

3. Polysaccharide + many H2Omany monosaccharide units


Chapter 12 carbohydrates

Monosaccharides

A carbohydrate that cannot be split or hydrolyzed into smaller carbohydrates.

  • Monosaccharides are carbohydrates with:

  • 3-9 carbon atoms

  • A carbonyl group (aldehyde or ketone)

  • Several hydroxyl groups

Cn(H2O)n

CnH2nOn

C ─ H

H─ C ─ OH

H─ C ─ OH

CH2OH

O


Chapter 12 carbohydrates

Monosaccharides - Aldose

O

C ─ H aldose

H─ C ─ OH

H─ C ─ OH

CH2OH

an aldotetrose

(Erythose)

  • Aldose is monosaccharide:

  • With an aldehyde group and many hydroxyl (-OH) groups.

  • triose (3C atoms)

  • tetrose (4C atoms)

  • pentose (5 C atoms)

  • hexose (6 C atoms)

  • “Aldo-” + suffix


Chapter 12 carbohydrates

Monosaccharides - Ketose

CH2OH

C = O ketose

H─ C ─ OH

H─ C ─ OH

H─ C ─ OH

CH2OH

a ketohexose

(Fructose)

  • Ketose is monosaccharide:

  • With a ketone group and many hydroxyl (-OH) groups.

  • triose (3C atoms)

  • tetrose (4C atoms)

  • pentose (5 C atoms)

  • hexose (6 C atoms)

  • “Keto-” + suffix


Chapter 12 carbohydrates

Some important Monosaccharides

  • Glucose

  • (C6H12O6, aldohexose) – blood sugar

  • Is found in fruits, vegetables,

  • corn syrup, and honey.

  • Is found in disaccharides such as sucrose, lactose, and maltose.

  • Makes up polysaccharides such as starch, cellulose, and glycogen.


Chapter 12 carbohydrates

Some important Monosaccharides

  • Fructose

  • (C6H12O6, ketohexose),

  • Is the sweetest of the carbohydrates.

  • Is found in fruit juices and honey (fruit sugar).

  • In bloodstream, it is converted to its isomer, glucose.

  • Is bonded to glucose in sucrose (a disaccharide known as table sugar).


Chapter 12 carbohydrates

Some important Monosaccharides

  • Galactose

  • (C6H12O6, aldohexose),

  • Has a similar structure to glucose except for the –OH on Carbon 4.

  • Cannot find in the free form in nature.

  • Exist in the cellular membranes of the brain and nervous system.

  • Combines with glucose in lactose (a disaccharide and a sugar in milk).


Chapter 12 carbohydrates

Disease - Galactosemia

Galactosemia

missing the enzyme that convert galactose to glucose.

Accumulation of galactose in the blood and tissues.

Mental retardation and cataract

Solution: removing the galactose from food: no milk.


Chapter 12 carbohydrates

C

H

O

Convert to Fischer

Projection

C

H

O

H

O

H

H

C

O

H

C

H

O

H

C

H

O

H

2

2

Fischer Projections

  • - Horizontal lines represent bonds projecting forward from the stereocenter.

  • - Vertical lines represent bonds projecting to the rear.

  • - Only the stereocenter is in the plane.

3D

2D


Chapter 12 carbohydrates

Fischer Projections

1. Carbon with four different groups bonded to it.

2. The chiral carbon furthest from the carbonyl group (-CHO).

H

HO

L - glucose

D - glucose

More common in the nature


Chapter 12 carbohydrates

Amino Sugars

  • - Amino sugars contain an -NH2 group in place of an -OH group.

    • - Only three amino sugars are common in nature:

    • D-glucosamine, D-mannosamine, and D-galactosamine.


Chapter 12 carbohydrates

Cyclic Structure – Haworth Structure

  • - Aldehydes and ketones react with alcohols to form hemiacetals.

  • - Cyclic hemiacetals form readily when the hydroxyl and carbonyl groups

    • are part of the same molecule.


Chapter 12 carbohydrates

Cyclic Structure – Haworth Structure

1

1

Anomeric carbon

1

1

1

Alpha (α)

Beta ()

More stable form

Anomers


Chapter 12 carbohydrates

Cyclic Structure – Haworth Structure

1

1

-Glucose-Glucose

1

1

-Galactose-Galactose


Chapter 12 carbohydrates

CH2OH

OH

HOCH2

HOCH2

2

2

HO

HO

H

H

H

OH

H

CH2OH

OH

H

OH

H

-fructose-fructose

Cyclic Structure – Haworth Structure

Anomeric carbon


Chapter 12 carbohydrates

Cyclic Structure – Haworth Structure

1

1

-Glucose-Glucose

Humans have -amylase (an enzyme) and they can digest starch

products such as pasta (contain-glucose)

Humans do not have β-amylase (an enzyme) and they cannot digest

cellulose such as wood or paper (containβ-glucose)


Chapter 12 carbohydrates

Chair Conformation

-D-Glucose

(Haworth projection)

-D-Glucose

(Chair conformation)


Chapter 12 carbohydrates

-D-glucose

Open-chain form

α-D-glucose

Mutarotation

Change in specific rotation that accompanies the equilibration

of αand  anomers in aqueous solution.

36%

64%

< 0.02%


Chapter 12 carbohydrates

Physical properties of Monosaccharides

  • Colorless

  • Crystalline solids

  • Soluble in water (H-bond because of OH groups)

  • Insoluble in nonpolar solvents


Chapter 12 carbohydrates

Chemical properties of Monosaccharides

  • Formation of Glycosides (acetals)

  • Oxidation

  • Reduction


Chapter 12 carbohydrates

- Exist almost exclusively in cyclic hemiacetal forms.

- They react with an alcohol to give acetals.

- Acetals are stable in water and bases but they are hydrolyzed in acids.

-D-Glucose

Methyl α-D-Glucoside

Methyl -D-Glucoside

Formation of Glycosides (acetals)


Chapter 12 carbohydrates

OH

Oxidation

+ Cu2O(s)

+ 2Cu2+

(Brike red)

Benedict’s

Reagent (blue)

D - glucose

D – gluconic acid

Oxidation of Monosaccharides

Aldonic acids

Reducing sugars: reduce another substance.


Chapter 12 carbohydrates

Oxidation of Monosaccharides

O

H

CH2OH

C

Rearrangement

(Tautomerism)

C = O

H

C OH

D-fructose

(ketose)

D-glucose

(aldose)


Chapter 12 carbohydrates

Enzyme

D-glucuronic acid

(a uronic acid)

D-glucose

Oxidation of Monosaccharides

primary alcohol at C-6 of a hexose is oxidized to uronic acid

by an enzyme (catalyst).

Exist in connective tissue

Detoxifies foreign phenols and alcohols


Chapter 12 carbohydrates

CH2OH

H2

D - glucose

D – Sorbitol (D – glucitol)

Reduction of Monosaccharides

Alditols

Transition metals

Sugars alcohols: sweetners in many sugar-free (diet drinks & sugarless gum).

Problem: diarrhea and cataract


Chapter 12 carbohydrates

Disaccharides

  • A disaccharide:

  • Consists of two monosaccharides linked by a glycosidic bond(when one –OH group reacts with another –OH group).

  • Glucose + glucose maltose + H2O

  • Glucose + galactoselactose + H2O

  • Glucose + fructosesucrose + H2O


Chapter 12 carbohydrates

Disaccharides

  • Maltose:

  • Is a disaccharide of two glucose molecules.

  • Has a α -1,4-glycosidic bond (between two α-glucoses).

  • Is obtained from the breakdown of starches.

  • Is used in cereals and candies.

  • Is a reducing sugar (carbon 1 can open to give a free aldehyde to oxidize).

 -1,4-glycosidic

bond

+

1

1

4

4

α-glucose

α-glucose

- maltose


Chapter 12 carbohydrates

Disaccharides

  • Lactose:

  • Is a disaccharide of galactose and glucose.

  • Has a β -1,4-glycosidicbond (between β-galactoseandα-gulcose).

  • Is found in milk and milk products (almost no sweet).

  • Is a reducing sugar(carbon 1 can open to give a free aldehyde to oxidize).

-lactose


Chapter 12 carbohydrates

Disaccharides

  • Sucrose:

  • Is found in table sugar (obtained from sugar cane and sugar beets).

  • Consists of glucose and fructose.

  • Has an α,β-1,2-glycosidic bond(between α-glucose and -fructose).

  • Is not a reducing sugar(carbon 1 cannot open to give a free aldehyde

  • to oxidize).


Chapter 12 carbohydrates

Polysaccharides

  • Polymers of many monosaccharides units.

  • Amylose (20%)

  • Starch

  • Amylopectin (80%)

  • Glycogen(animal starch in muscle and liver. It is

  • hydrolyzed in our cells and provides energy ).

  • Cellulose(plant and wood structures).

(starch that stores glucose in plants such

as rice, potatoes, beans, and wheat - energy storage).


Chapter 12 carbohydrates

Polysaccharides

  • Amylose:

  • Is a polysaccharide of α-glucose in a

  • continuous (unbranched) chain (helical or coil

  • form).

  • Has α-1,4-glycosidic bonds between the

  • α-glucose units (250 to 4000 units).

α-1,4-glycosidic bond


Chapter 12 carbohydrates

Polysaccharides

  • Amylopectin:

  • Is a polysaccharide of glucose units in branched chains.

  • Has α-1,4-glycosidic bonds between the α-glucose units.

  • Has α-1,6 bonds to branches of glucose units.

  • (at about every 25 glucose units, there is a branch).

  • Glycogen has same structure (more highly branched-every 10-15 units).


Chapter 12 carbohydrates

Polysaccharides

Amlose, Amylopectin (starch)

H+ or amylase (enzyme in saliva)

Digestion process

Dextrins (6-8 glucose units)

H+ or amylase (enzyme in saliva)

Maltose (2 glucose units)

H+ or maltase (enzyme)

Many α-D-glucose units


Chapter 12 carbohydrates

Respiration

C6H12O6 + 6O2 6CO2 + 6H2O + energy

glucose

Fermentation

Yeast

C6H12O6 2C2H5OH + CO2 + energy

Ethanol


Chapter 12 carbohydrates

Polysaccharides

  • Cellulose:

  • Is a polysaccharide of glucose units in unbranched chains with ß-1,4-glycosidic bonds (2200 glucose units).

  • Has rigid structure (H-bond) and insoluble in water.

  • Is the major structural material of wood & plants (cotton: 100%).

  • Cannot be digested by humans because of the

  • ß-1,4-glycosidic bonds (needs a special enzyme).


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