BIOMEDICAL SCIENCES BIOMEDICAL SCIENCES COURSESCOURSES

PRINCIPLES OF PRINCIPLES OF BIOMOLECULARBIOMOLECULAR

PART-1 CARBOHIDRATESPART-1 CARBOHIDRATES

INTRODUCTIONINTRODUCTIONFocus of this section are :

The important role of carbohydrate as a macrobiomolecular in life

Classification of Carbohydrate Physical-chemistry aspect of Carbohydrate Functional group and reaction of Carbohydrate

SOME ASPECT OF CARBOHYDRATE IN LIFESOME ASPECT OF CARBOHYDRATE IN LIFE Carbohydrates is one among the largest and most

important classes of naturally occurring organic substances. The simplest carbohydrates (saccharides and sugars) are formed in plant by a process called photosynthesis from carbon dioxide and water. This fundamental process of life is catalyzed by green plant pigment chlorophyll a and an enzyme systems, and liberates oxygen

Many important biopolymer consist of numerous units of simpler carbohydrates

Together with fats and protein, carbohydrates are fundamental energy carriers in our foods.

The conversion or decomposition of each molecules of (+) glucose to CO2 and H2O liberates kilocalories of energy.

This process of carbohydrate metabolism is catalyzed by enzymes

CLASSIFICATION OF CARBOHYDRATECLASSIFICATION OF CARBOHYDRATE The word “Carbohydrate” firstly means hydrates

of Carbon In term of its organic structures (related to the

containing functional group), Carbohydrates defined as : polyhydroxy aldehyde or polyhydroxy ketone

Carbohydrates also can classified according to the unit of its formation : monosaccharide, oligosaccharides, polysaccharides. The term of saccharides means sweet sugar (a simple unit of carbohydrates)

Relationship between those three form mono, oligo, and polysaccharides appear in the hydrolysis process

MONOSACCARIDESMONOSACCARIDES Introduction Monosaccharide can classified according to the number of

Carbon atom present ( triose, tetrose, pentose, hexose, and so on)

Or according to wheter the carbonyl group is p[resent as an aldehyde (aldose) or ketone (ketosa)

All of the monosccharide homologs actually starting from the very simple molecules which is Glycerol

H

H

OHOH

OH

HH

H

Glycerol

MONOSACCARIDESMONOSACCARIDES Sterochemistry of monosaccharides

C

CH 2OH

O

Dihidroksiaseton D-ribosa D-fruktosa

C

CH OH

CH OH

CH 2OH

CHO

CH OH

H

CH OH

CH 2OH

C

CH 2OH

O

CH 2OH O

CH 2OH

MONOSACCARIDESMONOSACCARIDES Ring formation of monosaccharides

As noted above, the preferred structural form of many monosaccharides may be that of a cyclic hemiacetal. Five and six-membered rings are favored over other ring sizes because of their low angle and eclipsing strain. Cyclic structures of this kind are termed furanose (five-membered) or pyranose (six-membered), reflecting the ring size relationship to the common heterocyclic compounds furan and pyran shown on the right. Ribose, an important aldopentose, commonly adopts a furanose structure, as shown in the following illustration. By convention for the D-family, the five-membered furanose ring is drawn in an edgewise projection with the ring oxygen positioned away from the viewer. The anomeric carbon atom (colored red here) is placed on the right. The upper bond to this carbon is defined as beta, the lower bond then is alpha.

MONOSACCARIDESMONOSACCARIDES Ring formation of monosaccharides (furanose

ring) pyranose and furanose ring

Diagram β-D-ribofuranose

MONOSACCARIDESMONOSACCARIDES Fischer and Howorth conformational structure of

monosaccharides

C

OHH

OHH

OHH

H

CH2OH

HO

H

O

1

2

3

4

5

6

HO

H

CH2OH

OH

H

O

OH

H

HC

C

C C

C OHH1

23

4

5

6

Fischer Haworth

MONOSACCARIDESMONOSACCARIDES Important reaction of monosaccharideso Oxidation

MONOSACCARIDESMONOSACCARIDES• Reduction

CH2OH

OHH

HHO

OHH

OHH

CH2OH

CHO

OHH

HHO

OHH

OHH

CH2OH

H2/ katalis

D-glusitol (surbitol)D-glukosa

• Glucosidation

HO

H

CH2OH

OH

H

O

OH

H

HC

C

C C

C

OH

H

HO

H

CH2OH

OH

H

O

OH

H

HC

C

C C

C

OCH3

HCH3-OH

H++ H2O

• Esterification

HO

H

CH2OH

OH

H

O

OH

H

HC

C

C C

C

OH

H

AcO

H

CH2Ac

OAc

H

O

OAc

H

HC

C

C C

C

OAc

H(CH3-CO)2O

MONOSACCARIDESMONOSACCARIDESo Osazone Formation

The osazone reaction was used to identify aldose sugars differing in configuration only at the alpha-carbon. The upper equation shows the general form of the osazone reaction, which effects an alpha-carbon oxidation with formation of a bis-phenylhydrazone, known as an osazone. Application of the osazone reaction to D-glucose and D-mannose demonstrates that these compounds differ in configuration only at C-2.

FORMATION OF MONOSACCARIDE RINGFORMATION OF MONOSACCARIDE RING Monosaccharides mainly existing in the

cyclic hemiacetal form. Two different crystalline forms of glucose were reported in 1895. Each of these gave all the characteristic reactions of glucose, and when dissolved in water equilibrated to the same mixture. This equilibration takes place over a period of many minutes, and the change in optical activity that occurs is called mutarotation. These facts are summarized in the diagram below.

FORMATION OF MONOSACCARIDE RINGFORMATION OF MONOSACCARIDE RING Formation of a ring in monosaccharides is achieved by

converting the open aldehyde structure for glucose into a cyclic hemiacetal, called a glucopyranose. The linear aldehyde is tipped on its side, and rotation about the C4-C5 bond brings the C5-hydroxyl function close to the aldehyde carbon. The hemiacetal carbon atom (C-1) becomes a new stereogenic center, commonly referred to as the anomeric carbon, and the α and β-isomers are called anomers.

GlycosidesGlycosidesAcetal derivatives formed when a monosaccharide reacts with an alcohol in the presence of an acid catalyst are called glycosides. This reaction is illustrated for glucose and methanol in the diagram below.

DISACCARIDESDISACCARIDESWhen the alcohol component of a glycoside is provided by a hydroxyl function on another monosaccharide, the compound is called a disaccharide.

POLYSACCARIDESPOLYSACCARIDESAs the name implies, polysaccharides are large high-molecular weight molecules constructed by joining monosaccharide units together by glycosidic bonds. They are sometimes called glycans. The most important compounds in this class, cellulose, starch and glycogen are all polymers of glucose. This is easily demonstrated by acid-catalyzed hydrolysis to the monosaccharide.