Carbohydrates

1Carbohydrates Chapter 1

Carbohydrates Chapter 1

DR. LEONARDO C. MEDINA, JR.

2Chapter Outline1. Carbohydrates: A First Class of Biochemicals2. Classification of

Carbohydrates3. Importance of

Carbohydrates

4. Monosaccharides

5. Structure of Glucose and Other Aldoses

3Chapter Outline (continued)

6. Cyclic Structure of Glucose; Mutarotation

7. Hemiacetals and Acetals8. Structures of Galactose

and Fructose9. Pentoses10. Disaccharides

11. Structures and Properties of Disaccharides

12. Sweeteners and Diet13. Redox Reactions of

Monosaccharides14. Polysaccharides Derived

from Glucose

4Carbohydrates: Carbohydrates: A First Class of A First Class of BiochemicalsBiochemicals

5 Carbohydrates are generally defined as polyhydroxy aldehydes or ketones or substances that yield these compounds when hydrolyzed.

H

CHO

C OH

C OHH

H

glyceraldehyde

C

C O

C OHH

H

dihydroxyacetone

H OH

H

6Classification Classification of of

CarbohydratesCarbohydrates

7A carbohydrate can be classified as:

1.monosaccharide

2.disaccharide

3.oligosaccharide

4.polysaccharide

8Monosaccharides A monosaccharide is a carbohydrate that

cannot be hydrolyzed to simpler carbohydrate units.

The monosaccharide is the basic carbohydrate unit of cellular metabolism.

9Disaccharides A disaccharide yields two

monosaccharides either alike or different when hydrolyzed:

disaccharide + water

2 monosaccharidesH+ or

enzymes

10

Monosaccharides & Disaccharides Disaccharides are often used by plants or

animals to transport monosaccharides from one cell to another.

The monosaccharides and disaccharides generally have the ending ose for example, glucose, sucrose, and lactose.

These are water-soluble carbohydrates, which have a characteristically sweet taste and are called sugars.

11

Oligosaccharides

An oligosaccharide has two to six monosaccharide units linked together.

12

Polysaccharides A polysaccharide is a macromolecular substance

that can be hydrolyzed to yield many monosaccharide units:

polysaccharide + water

monosaccharidesH+ or

enzymes

Polysaccharides are important structural supports, particularly in plants, and also serve as a storage depot for monosaccharides, which cells use for energy.

13

Other Ways to Classify Carbohydrates As a triose, tetrose, pentose, hexose, or

heptose As an aldose or ketose As a D or L isomer As a (+) or (-) isomer As a furanose or a pyranose As having an alpha () or beta ()

configuration

14

Importance of Importance of CarbohydratesCarbohydrates

15

Importance of Carbohydrates

1. Carbohydrates are very effective energy-yielding nutrients.

2. Carbohydrates can serve as very effective building materials.

3. Carbohydrates are important water- soluble molecules.

16

MonosaccharidesMonosaccharidesMonosaccharides

17

Monosaccharides

The hexose monosaccharides are the most important carbohydrate sources of cellular energy.

Three hexoses glucose, galactose, and fructose are of major significance in nutrition. All three have the same formula, C6 H12 O6 , and

thus deliver the same amount of cellular energy. They differ in structure, but are biologically

interconvertible.

18

Glucose (dextrose) is the most important of the monosaccharides.

It is an aldohexose and is found in the free state in plant and animal tissue.

H

CHO

OH

HHO

OHH

OHH

CH2OH

19

Galactose is also an aldohexose and occurs, along with glucose, in lactose and in many oligo- and polysaccharides such as pectin and gums.

H

CHO

OH

HHO

HHO

OHH

CH2OH

20

Fructose, also know as levulose, is a ketohexose that occurs in fruit juices, honey, and along with glucose, as a constituent of sucrose.

CH2OH

O

HHO

OHH

OHH

CH2OH

21

Structures of Glucose Structures of Glucose and Other and Other AldosesAldoses

22

Epimers Any two monosaccharides that differ

only in the configuration around a single carbon atom are called epimers.

D- and L-glyceraldehyde are epimers.

H

CHO

C OH

CH2OH

D-glyceraldehyde

HO

CHO

C H

CH2OH

L-glyceraldehyde

23

Configurations of the D-family of aldoses. The hydroxyl group on the new chiral carbon atom, added in going from triose to tetrose to pentose to hexose, is shown in red.

24


25


26

An example of the Kilani-Fischer synthesis in which two aldotetrose molecules are formed from an aldotriose molecule.

27

Cyclic Structure of Cyclic Structure of Glucose; Glucose; MutarotationMutarotation

28

Mutarotation of D-glucose

29

Anomers

When two cyclic isomers differ only in their stereo arrangement about the carbon involved in mutarotation, they are called anomers.

Mutarotation is the process by which anomers are interconverted.

30

Three-dimensional representations of the chair form of -D-glucopyranose

31

Hemiacetals and Acetals

HemiacetalsHemiacetals and and AcetalsAcetals

32

Cyclic structures of monosaccharides are intramolecular hemiacetals.

Five- or six-membered rings are especially stable.

O

CH2OH

HO

HO

OH

HO

hemiacetal structure in -D-glucopyranose

33

Glycoside When a monosaccharide hemiacetal reacts with

an alcohol, the product is an acetal. In carbohydrate terminology, this acetal

structure is called a glycoside.

O

CH2OH

RO

HO

OH

HO

acetal structure

glycosidic linkage

34

Structures of Structures of GalactoseGalactose and Fructoseand Fructose

35

Galactose

O

CH2OH

HO

OH

OH

OH O

CH2OH

HO

OH

OHOHH

CHO

OH

HHO

HHO

OHH

CH2OH

D-galactose -D-galactopyranose -D-galactopyranose

36

FructoseCH2OH

O

HHO

OHH

OHH

CH2OH

O

OH

CH2OH

OH

OH

CH2OH

37

DisaccharidesDisaccharidesDisaccharides

38

Disaccharides Disaccharides are carbohydrates composed

of two monosaccharide residues united by a glycosidic linkage.

sucrose + water

glucose + fructose

lactose + water

galactose + glucose

maltose + water

glucose + glucose

H+ or sucrase

H+ or

lactase

H+ or

maltase

39

Structures and Properties of Disaccharides

Structures and Structures and Properties of Properties of DisaccharidesDisaccharides

40

Disaccharides contain an acetal structure (glycosidic linkage), and some also contain a hemiacetal structure.

Maltose: O

CH2OH

O

OH

HO

OH

O

CH2OH

HO

HO

OH

-1,4-glycosidic linkage

41

Sweeteners and Diet Sweeteners Sweeteners and Dietand Diet

43

Redox Reactions of Monosaccharides

RedoxRedox Reactions of Reactions of MonosaccharidesMonosaccharides

44

Oxidation The aldehyde groups in monosaccharides can

be oxidized to monocarboxylic acids by mild oxidizing agents such as bromine water.

H

CHO

OH

HHO

OHH

OHH

CH2OH

+ Br2 + H2O

H

COOH

OH

HHO

OHH

OHH

CH2OH

+ 2HBr

45

Reduction Monosaccharides can be reduced to their

corresponding polyhydroxy alcohols by reducing agents such as H2 /Pt or sodium amalgam, Na(Hg).

H

CHO

OH

HHO

OHH

OHH

CH2OH

+ H2 / Pt

H

CH2OH

OH

HHO

OHH

OHH

CH2OH

46

Redox Test for Carbohydrates

Under prescribed conditions, some sugars reduce silver ions to free silver, and copper (II) ions to copper (I) ions.

Such sugars are called reducing sugars.

47

Polysaccharides Derived from

Glucose

Polysaccharides Polysaccharides Derived from Derived from

GlucoseGlucose

48

Starch Starch is found in plants, mainly in the seeds,

roots, or tubers. Corn, wheat potatoes, rice and cassava are the

chief sources of dietary starch. The two main components of starch are

amylose and amylopectin. Amylose molecules are unbranched chains

composed of about 25-1300 -D-glucose units joined by -1,4-glycosidic linkages.

49

Representation of amylose.

52

Glycogen Glycogen is the energy-storage carbohydrate of

the animal kingdom. It is formed by the polymerization of glucose

and is stored in the liver and in muscle tissues. Structurally, it is very similar to the

amylopectin fraction of starch, except that it is more highly branched.

The -1,6-glycosidic linkages occur on one of every 12-18 glucose units.

53

Cellulose

Cellulose is the most abundant organic substance found in nature.

It is the chief structural component of plants and wood.

54

Two representations of cellulose. In the three- dimensional drawing, note the hydrogen bonding that links the extended cellulose polymers to form cellulose fibers.

55

Carbohydrates Chapter 1Chapter OutlineChapter Outline (continued)Carbohydrates: A First Class of BiochemicalsSlide Number 5Slide Number 6Slide Number 7MonosaccharidesDisaccharidesMonosaccharides & DisaccharidesOligosaccharidesPolysaccharidesOther Ways to Classify CarbohydratesImportance of CarbohydratesImportance of CarbohydratesMonosaccharidesMonosaccharidesSlide Number 18Slide Number 19Slide Number 20Structures of Glucose and Other AldosesEpimersSlide Number 23Slide Number 24Slide Number 25Slide Number 26Cyclic Structure of Glucose; MutarotationSlide Number 28AnomersSlide Number 30Hemiacetals and AcetalsSlide Number 32GlycosideStructures of Galactose and FructoseGalactoseSlide Number 36DisaccharidesDisaccharidesStructures and Properties of DisaccharidesSlide Number 40Slide Number 41Slide Number 42Redox Reactions of MonosaccharidesOxidationSlide Number 45Redox Test for CarbohydratesPolysaccharides Derived from GlucoseStarchSlide Number 49Slide Number 50Slide Number 51Slide Number 52Slide Number 53Slide Number 54Slide Number 55

Carbohydrates

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