L. Noha Soliman Carbohydrates Objectives Introduction.. Functions Of Carbohydrates. Types Of...

L. Noha Soliman

Carbohydrates

Biochemistry(BMS 233)

Carbohydrates

Objectives

Introduction. Functions Of Carbohydrates. Types Of Carbohydrates.Classification Of Carbohydrates.MONOSACCHARIDES

• Monosaccharide Classification. • Some important monosaccharides and their

structures.• Sugars exhibit various forms of isomerism

DISACCHARIDESPOLYSACCHARIDES

Introduction

Also called saccharides , which means “sugars.”

They composed of carbon, hydrogen, and oxygen in a 1:2:1 empirical ratio.

The general empirical formula for a carbohydrate is CH2O. If a carbohydrate has 5 carbons atoms, what would be its empirical formula? If a carbohydrate has 12 hydrogen atoms present, what would be its empirical formula?

All carbohydrates have this empirical formula except deoxy sugars, amino sugars.

Most carbohydrates end with the suffix –ose.

C5H10O5

C6H12O6

Are produced by photosynthesis in plants.

Such as glucose are synthesized in plants from CO2, H2O, and light energy from the sun.

Are oxidized in living cells (respiration) to produce CO2, H2O, and energy.

Introduction

Functions of Carbohydrates

Provide energy source:• Living things use carbohydrates as their main source of energy.

• The breakdown of sugar supplies immediate energy for all cell activities.

Provide energy storage:• Plants store energy in a complex carbohydrate form called starch.

• Animals store energy in a complex carbohydrate in their muscle tissue and liver in the called glycogen.

Functions of Carbohydrates

Structural Building Material:

• Plants and some animals also use carbohydrates for structural purposes.

• Plants build their cell walls of a complex carbohydrate called cellulose.

• Animals such as arthropods build their exoskeletons of a complex carbohydrate called chitin.

• Chitin is also found in the cell walls of Fungi.

Carbohydrates are chains (polymers) made of monomers.

The most common monomer of carbohydrates is…

There are

2 types

of

carbohydrates

Simple Complex

Simple Sugars are carbohydrates made up of 1 or 2 monomers.

They taste sweet.

Complex Cabohydrates are polymers made up of many monomers.

Most taste starchy.

Classes of Carbohydrates

Classifications based on number of sugar units in

total chain:

Monosaccharides - single sugar unit

Disaccharides - two sugar units

Oligosaccharides- 3 to 10 sugar units

Polysaccharides- more than 10 units

Classes of Carbohydrates

MONOSACCHARIDES

The basic building blocks (monomers) of carbohydrates. (cannot be further hydrolyzed into smaller units).

Known as simple sugars.

Readily soluble in water.

Same no. of C as O atoms. e.g. Glucose is C6H12O6

Have the general formula (CH2O)n They contain:

– a carbonyl group (C=O) – either at 1C atom or at the 2C atom – multiple hydroxyl groups (-OH)

White crystalline solids.

Structural representation of sugars

Fisher projection: straight chain form. Haworth projection: simple ring. Chair form.

D-Glucose

α- D-Glucose

α- D-Glucose

Monosaccharide Classification

MONOSACCHARIDE

FUNCTIONAL GROUP

ALDOSE KETOSE

NUMBER OF CARBONS IN THE BACKBONE

TRIOSE PENTOSE HEXOSE

Monosaccharide Classification

OH

OH

H

H

HO

CH2OH

HH

H

OH

O

Glucose

H

OH

HO

O H

HHO

H

Ribose

CH2OH

Glyceraldehyde

H

H

H

H

OH

OH

O

C

C

C

65 3

Classified by number of carbons:3C = triose (glyceraldehyde)5C = pentose (ribose)6C = hexose (glucose)

TRIOSES PENTOSES HEXOSES

contains 3 carbon atoms contains 5 carbon atoms contains 6 carbon atoms

C3H6O3 C5H10O5 C6H12O6

glyceraldehydes dihydroxyacetone

ribose deoxyribose

glucose immediate source of energy for cellular

respiration

building blocks to form larger molecules

components of nucleic acids

galactose sugar found in milk and

yogurt

fructose sugar found in honey

Monosaccharide Classification

Monosaccharide Classification

It can be classified based on functional group(According to where the carbonyl group is located): • Aldose - polyhydroxyl aldehyde (aldehyde sugar):

with the carbonyl group (C=O) at the first carbon position, which forms an aldehyde group (CHO).

• Ketose - polyhydroxyl ketone (ketone sugar):Carbonyl group is at C2 position.

1

2

1

2

Monosaccharide Classification

Both functional group have reducing properties ~ reducing sugars

ALDOSES KETOSES

carbonyl group (C=O) at 1C is the aldehyde group

carbonyl group (C=O) at 2C is the ketone group

sugar is known as aldose (aldehyde sugar)

sugar is known as ketose (ketone sugar)

glucose fructose

Monosaccharide Classification

Learning check

Identify each as aldo- or keto- and as tetrose, pentose, or hexose:

H

CH2OH

OHC

H

H

H

OH

OH

OH

C

C

C

HC

O

CH2OH

HHO

CH2OH

O

H OHC

C

C

Aldohexose Ketopentose

Some important monosaccharides

Glucose:• In plants and fruits.• Mild sweet flavor.• known as blood sugar.• Essential energy source.Fructose:• Sweetest sugar• Found in fruits and honey.• Added to soft drinks, cereals, deserts.

Galactose:• Part of milk sugar.• Hardly tastes sweet.• Rarely found naturally as a single sugar.

Some important monosaccharides

Glyceraldehyde Simplest sugar

Ribose Found in RNA

Deoxyribose Found in DNA

Glyceraldehyde

SUGARS EXHIBIT

VARIOUS FORMS

OF ISOMERISM

SUGARS ISOMERISM

They are molecules which have the same molecular formula but have different structures.

Glucose and fructose both have the empirical formula C6H12O6

but they have different structural formulas or shapes.

1. Aldose – Ketose Isomerism: (Isomers)

•Asymmetric carbon: Cl

4 different things are attached to it. |•You must have at least one asymmetric I - C - F carbon to have stereoisomers. |

Br

Chiral center H

| C=O | H-C-OH |

CH2OH Chiral centerGlyceraldehyde

Chiral center

Physical properties

• Optical activityability to rotate plane polarized light.

• Dextrorotatory - rotate to right

- use + symbol

- usually D isomers• Levorotatory - rotate to left

- use - symbol

- usually L isomers

Light is passed through a polarized filter.

A solution of an optical isomer will rotate the light one direction.

2. D and L Isomerism: (Enantiomers)

• Pairs of structures that are mirror images of each other and CANNOT be superimposed on each other.

• Designated by D- or L- at the start of the name.

O H O H C C H – C – OH HO – C – H

HO – C – H H – C – OH

H – C – OH HO – C – H

H – C – OH HO – C – H

CH2OH CH2OH

D-glucose L-glucose

2. D and L Isomerism: (Enantiomers)

3. Epimers:

• Two sugars that differ in configuration at only one chiral center.

• The most important epimers of glucose are:

Mannose epimerization at C2

Galactose epimerization at C4

Hemiacetal & hemiketal formation:

An aldehyde can react with an alcohol to form a hemiacetal.

A ketone can react 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

+

+

4. Pyranose and Furanose ring structures:

Pentoses and hexoses can cyclize as the ketone or aldehyde reacts with a distal OH.

Glucose forms an intra-molecular hemiacetal, as the C1 aldehyde & C5 OH react, to form a 6-member pyranose ring.

H O

OH

H

OHH

OH

CH2OH

H

OH

H H O

OH

H

OHH

OH

CH2OH

H

H

OH

-D-glucose -D-glucose

23

4

5

6

1 1

6

5

4

3 2

H

CHO

C OH

C HHO

C OHH

C OHH

CH2OH

1

5

2

3

4

6

D-glucose (linear form)

4. Pyranose and Furanose ring structures:

Fructose forms either• A 6-member pyranose ring, by reaction of the C2 keto group with

the OH on C6, or• A 5-member furanose ring, by reaction of the C2 keto group with

the OH on C5. CH2OH

C O

C HHO

C OHH

C OHH

CH2OH

HOH2C

OH

CH2OH

HOH H

H HO

O

1

6

5

4

3

2

6

5

4 3

2

1

D-fructose (linear) -D-fructofuranose

5. Alpha and beta anomers:

Cyclization of glucose produces a new asymmetric center at C1.

The 2 stereoisomers are called anomers, a & b. GLUCOSE

primary source of energy

- glucose - glucose

hydroxyl (-OH) group of the 1C projects below the

plane of the ring

hydroxyl (-OH) group of the 1C projects upward the

plane of the ring

DISACCHARIDES

These are formed when two monosaccharide molecules join together with the elimination of one molecule of water.

They have the general formula C12H22O11.

Sweet tasting.

Water soluble.

EXAMPLE: Maltose

Sucrose

Lactose

C6H12O6 + C6H12O6 = C12H22O11 + H2OGlucose + Glucose = Maltose + Water

CH2OH

H O H

OH OH

CH2OH

H O H

HO OH

+H20

CH2OH

H O H

OH

CH2OH

H O H

OHO

α- GLUCOSE α- GLUCOSE MALTOSE

Disaccharide Formation

Disaccharides are formed when two monosaccharides are joined by dehydration synthesis reaction.

GLUCOSE + GLUCOSE -> Maltose (malt sugar)GLUCOSE + FRUCTOSE -> Sucrose (cane sugar)GLUCOSE + GALACTOSE -> Lactose (milk sugar)

Dehydration Synthesis

• Building reaction.

• H2O is removed in order to form a new bond.

Hydrolysis Reaction

• Breaking reaction.

• H2O is required to break a bond.

Glycosidic linkage

• The bond between monosaccharides.• What type of reaction would form this bond?

– Dehydration synthesis reaction.• What kind of bond is a glycosidic linkage?

– Polar covalent bond.O

H2C

OH

CHO

HO

OH

OH

OH2C

OH

HOHO

OHOH

OH2C

OH

CHO

HO

OHO

H2C

OH

O

HO

OHOH

+ H2O

Disaccharide Formation

Some important disaccharides

• Sucrose: Saccharose or table sugar• It is fructose and glucose combined.

• Source of sucrose is sugar beets and sugar cane.

• Tastes sweet, and is readily available.

• brown, white, powdered.

Some important disaccharides

• Maltose: Malt sugar• Consists of two glucose units. • Produced when starch breaks down.• Not abundant.• Present in germinating seeds.

Lactose: milk sugar• Glucose and galactose.• Main carbohydrate in milk.

Some important disaccharides

OLIGOSACCHARIDES

• Oligosaccharide is a few linked monosaccharides and are at time associated with proteins (glycoproteins) or lipids (glycolipids).

POLYSACCHARIDES

Polysaccharides are chains of monosaccharides that have been joined by many dehydration synthesis reactions.

Do not taste sweet and do not crystallize.

Insoluble in water.

Form colloidal solutions when added to water.

Polysaccharide diversity

Molecular structure determines function.

The function of the polysaccharide depends on what type of isomer of glucose the polysaccharide is made.

Storage PolysaccharidesEnergy storage - starch and glycogen.

Structural PolysaccharidesUsed to provide protective walls to cells – cellulose and chitin.

In starch In cellulose

STORAGE POLYSACCHARIDES

STARCH AND

GLYCOGEN

Some important polysaccharides

Starch

Energy storage used by plants.– Storage form of glucose in plants.– Found in grains, tubers, and legumes.

Body hydrolyzes plant starch to glucose.

Long repeating chain of α-D-glucose.

Chains up to 4000 units.

Starch Starch consists of two compounds:

– Amylose: straight chain of α-D- glucose, major form of starch.

– Amylopectin: branched chains of α-D-glucose.

Glycogen

Energy storage of animals:– Storage form of glucose in the body.– Provides a rapid release of energy when needed.

Structure is similar to amylopectin but more branches.

Made from α-glucose.

Glycogen

Found mainly in liver and muscle cells.

When the level of glucose in your blood runs low, glycogen is released from your liver.

The glycogen stored in your muscles supplies the energy for muscle contraction and thus, for movement.

more branching

carbon and energy (glucose) storage molecules

STRUCTURAL POLYSACCHARIDES CELLULOSE

AND CHITIN

Some important polysaccharides

Cellulose

Most abundant organic compound on Earth.

It forms the main part of the cell wall in plants cells.

Cellulose is the major component of cotton , wood and paper.

Cellulose

It is a polysaccharide of β glucose units in unbranched chains.

Linked by β-1,4 glycosidic bonds.

Each β-glucose related to the next by a rotation of 180°.

14

3 2

5

6

1 4 1 4 1 4

Cellulose

Every other glucose is flipped over, due to β linkages. This promotes intra-chain and inter-chain H-bonds and van der Waals interactions, that cause cellulose chains to be straight & rigid, and pack with a crystalline arrangement in thick bundles - microfibrils.

Digesting starch vs. cellulose

starcheasy todigest

starcheasy todigest enzyme

enzyme

cellulosehard todigest

cellulosehard todigest

Cowcan digest cellulose well; no need to eat other sugars

Gorillacan’t digest cellulose well; must add another sugar source, like fruit to diet

Digesting starch vs. cellulose

Amino derivatives

The replacement of a hydroxyl group on a carbohydrate results in an amino sugar.

•Uses for amino sugars.•Structural components of bacterial cell walls.•As a component of chitin.•A major structural unit of chondroitin sulfate - a component of cartilage.•Component of glycoprotein and glycolipids.

H O

OH

OH

H

H

OHH

OH

CH2OH

HH O

OH

OH

H

H

NH2H

OH

CH2OH

H

-D-glucose -D-2-aminoglucose (glucosamine)

Chitin

It is the “plastic-like” material that composes the exoskeletons of arthropods (insects, arachnids, and crustaceans).Most fungi (mushrooms) have chitin present within their cell walls.

Chitin

Similar to cellulose but the hydroxyl group on each monomer substituted with an acetyl amine group.

Cellulose strands are parallel, chitins can be parallel or antiparallel.

Above is a structural monomer of chitin.