Chemistry 20
Download
1 / 38

Chapter 12 Carbohydrates - PowerPoint PPT Presentation


  • 75 Views
  • Uploaded on
  • Presentation posted in: General

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.

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha

Download Presentation

Chapter 12 Carbohydrates

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


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.

Cn(H2O)n

Photosynthesis

6CO2 + 6H2O + energyC6H12O6 + 6O2

Respiration

glucose


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.


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


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


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


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


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.


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).


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).


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.


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


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


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.


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.


Cyclic Structure – Haworth Structure

1

1

Anomeric carbon

1

1

1

Alpha (α)

Beta ()

More stable form

Anomers


Cyclic Structure – Haworth Structure

1

1

-Glucose-Glucose

1

1

-Galactose-Galactose


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


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)


Chair Conformation

-D-Glucose

(Haworth projection)

-D-Glucose

(Chair conformation)


-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%


Physical properties of Monosaccharides

  • Colorless

  • Crystalline solids

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

  • Insoluble in nonpolar solvents


Chemical properties of Monosaccharides

  • Formation of Glycosides (acetals)

  • Oxidation

  • Reduction


- 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)


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.


Oxidation of Monosaccharides

O

H

CH2OH

C

Rearrangement

(Tautomerism)

C = O

H

C OH

D-fructose

(ketose)

D-glucose

(aldose)


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


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


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


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


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


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).


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).


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


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).


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


Respiration

C6H12O6 + 6O2 6CO2 + 6H2O + energy

glucose

Fermentation

Yeast

C6H12O6 2C2H5OH + CO2 + energy

Ethanol


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).


ad
  • Login