17-1

Principles and Applications of Inorganic, Organic, and

Biological ChemistryDenniston, Topping, and Caret

4th ed

Chapter 17

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Power Point to Accompany

17-2

Introduction• Carbohydrates are synthesized by

photosynthesis in plants.

• Grains, cereals, bread, sugar cane

• Glucose is major energy source

• A gram of digested carbohydrate gives about 4 kcal of energy

• Complex carbs are best for diet

• USDA recommends about 58% daily calories from carbs (not simple sugars)

17-3

17.1 Carbohydrate TypesMonosaccharides

E. g. glucose, fructoseone sugar (saccharide) molecule

DisaccharidesE. g. sucrose, lactoseTwo monosaccharides linked

PolysaccharidesE. g. starch, glycogen, celluloseChains of linked monosaccharide units

17-4

17.2 Monosaccharides

polyhydroxy

Aldehydesare aldoses

Ketonesareketoses

3=triose4=tetrose5=pentose6=hexose

Number of carbons

17-5

Three carbon monosaccharides

D-glyceraldehyde

Is an aldotriose

dihydroxy acetone

Is a ketotriose

C

C

O H

CH2OH

OHHCH2OH

C

CH2OH

O

17-6

17.3 Stereoisomers and StereochemistryPrefixes D- and L- in a monosaccharide

name identify one of two isomeric forms.

The isomers (same formula) differ in the spatial arrangement of atoms and are stereoisomers.

The stereoisomers D- and L- glycer- aldehyde are nonsuperimposable

mirror image molecules and are called enantiomers (a subset of stereoisomers).

17-7

Stereoisomers and StereochemistryMolecules that can exist in enantiomeric

forms are said to be chiral.

Chirality in glyceraldehyde is conveyed by a chiral (asymmetric) carbon-one with four different groups attached.

17-8

Glyceraldehyde has a stereocenter (chiral) carbon and thus has two enantiomers (nonsuperimposable mirror image molelcules)

The D isomer has the OH on the stereocenter to the right. The L isomer has the OH on the stereocenter to the left.

C

C

O H

CH2OH

OHH

C

C

O H

CH2OH

HOH

the D isomer the L isomer

Stereocenter:connected tofour different atoms or groups

Mirrorplane

17-9

Optical ActivityEnantiomers are also called optical isomers.

Pasteur, in 1848, showed that enantiomers interact with plain polarized light to rotate the plane of the light in opposite directions. This interaction with polarized light is called optical activity and distinguishes the isomers. It is measured in a device called a polarimeter.

A discussion of plane polarized light follows.

17-10

Polarized Light-1Normal light vibrates in an infinite number of directions perpendicular to the direction of travel. When the light passes through a polarizing filter (Polaroid sunglasses, for example) only light vibrating in one plane reaches the other side of the filter.The diagram on the next slide illustrates this idea. The diagram is of a polarimeter, the instrument used to measure rotation of plain polarized light.

17-11

Polarized Light-2

Light vibration inmany directions

Polarized light vibrating in vertical plane.

polarizerPolarized light planebeing rotated in sampletube.

Rotated beam

Analyzer polaroid

17-12

Optical Activity-againWhen an enantiomer in a solution is placed

in the polarimeter, the plane of rotation of the polarized light is rotated.

One enantiomer always rotates light in a clockwise (+) direction and is said to be the dextrorotatory isomer. The other isomer rotates the light in a counterclockwise (-) direction and is the levorotatory isomer.

Under identical conditions, the enantiomers always rotate light to exactly the same degree but in opposite directions.

17-13

Fischer ProjectionsA Fischer projection uses lines crossing

through a chiral carbon to represent bonds projecting out of the page (horizontal lines) or bonds projecting into the page (vertical lines).

Compare the wedge vs the Fischer pictures below for glyceraldehyde.

CHO

C

CH2OH

OHH

CHO

C

CH2OH

HOH

the D isomer the L isomer

CHO

CH2OH

OHH

CHO

CH2OH

HOH

17-14

The D- and L-SystemMonosaccharides are drawn in Fischer

projections with the most oxidized carbon closest to the top. The carbons are numbered from the top. If the chiral carbon with the highest number has the OH to the right, the sugar is D. If the OH is to the left, the sugar is L.

Most common sugars are in the D form.

17-15

C

C

O H

C

OHH

CH2OH

H OH

CH2OH

C

C

O

OH

C OHH

C

H

H OH

CH2OHD-erythrosean aldotetrose

D-fructosea ketohexose

1

2

3

4

1

2

3

4

5

6

17-16

CHO

C

C

OH

OH

C HOH

C

H

H OH

CH2OH

H

D-glucosean aldohexose

D-galactosean aldohexose

CHO

C

C

OH

OH

C OHH

C

H

H OH

CH2OH

H

These diastereomers are also epimers, they differ in configuration at only one stereocenter (colored dot).

17-17

17.4 Biological MonosaccharidesGlucose is the most important sugar in

the human body. Its concentration in the blood is regulated by insulin and glucagon.

Under physiological conditions, glucose exists in a cyclic hemiacetal form where the C-5 OH reacts with the aldehyde.

Two isomers (anomers) are formed which differ in the location of the OH on the acetal carbon, C-1. (Next slide)

17-18

Cyclic Form for GlucoseThe cyclic form of glucose is shown as a

Haworth projection.O

CH2OH

HH

OHH

OH

OH

HOH

H

OCH2OH

HH

OHH

OH

OH

H O

HH

OCH2OH

HH

OHH

OH

OH

HH

OH

form(alpha)

form(beta)

arrows showelectron movement

Pyranose ring form

Haworth projections

17-19

Cyclic Form for Glucose-cont.Fischer to Haworth projections

- D-glucose

C

C

C

OH

OH

C OHH

C

H

HHOCH2

H

OHH

O

1

2

3

4

5

6

ODraw ring with O at upper right.

OCH2OH

HH

OHH

OH

OH

HOH

H

Groups to the left go up on the Haworth ring.

1

23

6

4

5

17-20

Fructose (Levulose or Fruit Sugar)Found in honey, corn syrup, and sweet

fruits. The sweetest of sugars!

D-fructose

CH2OHCC

OOH

C OHHC

H

OHCH2OH

H

1

2

3

4

5

6

O CH2OHCH2OH

HOHH

OH

O

CH2OH

CH2OH

HOHH

OH

17-21

Galactose ( in lactose/milk sugar)

-D-galactoseamine is a component of the blood group antigens.

-D-galactose

CHOCC

OHOH

COH HC

H

OHCH2OH

H

H

1

2

3

4

5

6

OCH2OH

H

H

OH

H

OH

OH

HOH

H

17-22

RiboseRibose also exists mainly in the cyclic form

OHCCH2OH

H

CHO

CC

H OHH OH

CH2OH

HH

OH

H

OH

O H

OH

-D-riboseDeoxyribose has an H herereplacing the OH

17-23

Reducing Sugars

+ Cu2O (red-orange)

Aldehydes of aldoses are oxidized by Benedict’s reagent, an alkaline copper(II) solution. The blue color fades as reaction occurs and a ppt forms. Test measures glucose in urine.

CC

O H

CH2OHOHH

CC

O O

CH2OHOHH+2 Cu2+

17-24

Reducing SugarsAll monosaccharides and the disac-

charides except sucrose are reducing sugars. Ketoses can isomerize to aldoses.

D-glucose

CHCC

OHOH

C OHHC

H

H OHCH2OH

HO

D-fructose

CH2OHCC

OOH

C OHHC

H

H OHCH2OH

CHCC

OHOH

C OHHC

H

H OHCH2OH

OH

enediol

17-25

A Reduced SugarThe most important reduced sugar is deoxyribose. (In DNA)

CC

O H

CHH

CH OH

OHHCH2OH

D-deoxyribose -D-2-deoxyribose

O OH

H

CH2OH

HH

OH

H

H

17-26

17.5 DisaccharidesThe anomeric OH can react with another

OH on an alcohol or sugar. Water is lost to form an acetal.

O

CH2OH

HH

OHH

OH

OH

H

H

OH

+ CH3 OH

O

CH2OH

HH

OHH

OH

OH

H

H

O CH3

+ H2O

Acetal link: R-O-C-O-R

Acetalcarbon

17-27

Disaccharides: SucroseSucrose is formed by linking D-glucose

with D-fructose (acetal link=1) to give a 1,2 glycosidic link.

CH2

O H

OH H

OH

O H

CH2OH

OHO

CH2OH

HH

OH

H

OH

OH

H

H

1 2

Sucrose is table sugar and is linked to dental caries. It is nonreducing. The glycosidic O is part of an acetal and a ketal.

17-28

Disaccharides: LactoseLactose is formed by joining D-galactose to D-

glucose to give a 1,4 glycoside

O

CH2OH

H

H

OH

H

OH

OH

HH OH

O

CH2OH

HH

H

OH

OH

H

H

O1

-D-galactose

4

-D-glucoseLactose is milk sugar. Lactose intolerance

results from lack of lactase to hydrolyze the glycosidic link of lactose.

17-29

Disaccharides:GalactosemiaIn order for lactose to be used as an

energy source, galactose must be converted to a phosphorylated glucose molecule. When enzymes necessary for this conversion are absent, the genetic disease galactosemia results.

People who lack the enzyme lactase (~20%) are unable to digest lactose and have the condition called lactose intolerance.

17-30

Disaccharides: MaltoseMaltose is formed by linking two -D-glucose

molecules to give a 1,4 glycosidic link.

OH

OCH2OH

HH

H

OH

OH

H

H

O

OCH2OH

HH

OHH

OH

OH

HH

Maltose is malt sugar. It is formed when starch is partly hydrolyzed. It is a reducing sugar due to the free acetal.

17-31

Disaccharides:CellobioseCellobiose is formed by linking two D-

glucose molecules to give a 1,4 glycosidic link. It comes from hydrolyzed cellulose.

OCH2OH

HH

OHH

OH

OH

H H

OHOCH2OH

HH

H

OH

OH

H HO

17-32

17.6 Polysaccharides: CelluloseCellulose is the major structural polymer

in plants. It is a liner homopolymer composed of -D-glucose units linked -1,4. The repeating disaccharide of cellulose is -cellobiose.

Animals lack the enzymes necessary to hydrolyze cellulose. The bacteria in ruminants (eg. cows) can digest cellulose so that they can eat grass, etc.

17-33

Structure of Cellulose

OO

CH2OH

HH

OH

OH

OH

H HOCH2OH

HH

H

OH

OH

H HOO

CH2OH

HH

OH

OH

OH

H H

-(1->4) glycosidic bond

17-34

Polysaccharides: StarchStarches are storage forms of glucose

found in plants.They are polymers of linked glucose.If the links are only 1,4, the polymer is

linear and is called amylose. (Figure on next slide.) Amylose usually assumes a helical configuration with six glucose units per turn.

If the links are both 1,4 and 1,6, the polymer is branched and is called amylopectin. (Figure on next slide.

17-35

Polysaccharides: amylose/amylopectin

amylopectin(-1,6 link)

()

O

OCH2

HH

OH

OH

OH

HH

OHO

CH2

HH

OH

OH

OH

HH

OH

OCH2

HH

OH

OH

OH

HO

HOH

OCH2

HH

OH

OH

OH

HHO

CH2

HH

OH

OH

OH

HH

OHO

CH2

HH

OH

OH

OH

HH

OH

(

amylose(-1,4 links)

()

OHO

CH2

HH

OH

OH

OH

HO

HOH

OCH2

HH

OH

OH

OH

HHO

CH2

HH

OH

OH

OH

HH

OHO

CH2

HH

OH

OH

OH

HH

OH

17-36

Polysaccharides: glycogenThe storage carbohydrate in animals is

glycogen. It is a branched chain polymer like amylopectin but it has more frequent branching (about every 10 residues). Glycogen is stored in liver and muscle cells.

17-37

GlycoproteinsThese materials contain carbohydrate

residues on protein chains. Very important examples of these materials are antibodies-chemicals which bind to antigens and immobilize them.

The carbohydrate part of the glycoprotein plays a role in determining the part of the antigen molecule to which the antibody binds.

17-38

Glycoproteins: 2The human blood groups A, B, AB, and

O depend on the oligosaccharide part of the glycoprotein on the surface of erythrocyte cells. The terminal monosaccharide of the glycoprotein at the nonreducing end determines blood group.

17-39

Glycoproteins: 3

Type Terminal sugar

A N-acetylgalactosamine

B -D-galactose

AB both the above

O neither of the above

O is the “universal donor”

AB is the “universal acceptor”

17-40

The End

Carbohydrates