MONOSACCHARIDESMONOSACCHARIDES Monosaccharides are carbohydrates that

cannot be hydrolyzed to obtain smaller molecules of carbohydrate.

White crystalline solids , very soluble in water, have sweet taste.

# Carbons Category Name Relevant examples

3 Triose Glyceraldehyde, Dihydroxyacetone

4 Tetrose Erythrose

5 Pentose Ribose, Ribulose, Xylulose

6 Hexose Glucose, Galactose, Mannose, Fructose

7 Heptose Sedoheptulose

9 Nonose Neuraminic acid, also called sialic acid

Hexoses Hexoses Three common sugars share the same molecular

formula: C6H12O6. Because of their six carbon

atoms, each is a hexose. hexose.

They are:

glucoseglucose, "blood sugarblood sugar", the immediate source of

energy for cellular respiration

galactosegalactose, a sugar in milk (and yogurt), and

fructose, a sugar found in honey.

D-GlucoseD-Glucose (Grape Sugar)(Grape Sugar)

Glucose is by far the most common carbohydrate

and classified as a monosaccharide,

an an aldosealdose, ,

a a hexosehexose,

and is a reducing sugar.

It is known as dextrosedextrose, because it is

dextrorotatorydextrorotatory

For sugars with more than one chiral center, D or L refers to the asymmetric C farthest from the aldehyde or keto group.

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

OccurrenceOccurrence

Widely distributed in nature

Occurs in combination with other sugars forming disaccharides

SucroseSucrose MaltoseMaltose Lactose Lactose

Commercially obtained from starch

Glucose is also called blood sugar blood sugar

circulates in the blood at a concentration of 60-100 mg/dL 60-100 mg/dL of blood in the fasting condition

Normally trace amounts pass out in urine

Increased amounts in diabetes mellitus.

74% as sweet as sucrose74% as sweet as sucrose

ChemistryChemistry

Glucose can occur both in pyranose and furanose pyranose and furanose forms

O O

Pyranose furanose

PyranosePyranose form is more predominant due to stable ring

D-glucose: the chair conformer

OH

HH

H

HOH

H

O

OHOH

CH2OH

12

3

45

6

Four of the five bulky groups (OH and CH2OH on C 2,3,4,5)

on the ring are in the more stable equitorial positions!

D-fructose

Fruit sugarLevuloseLevulose

FructoseFructose Fructose is classified as a:

monosaccharide,

the most important ketose sugar,

a hexose,

and is a reducing sugar.

Fructose, along with glucose are the

monosaccharides found in disaccharide,

sucrose.

Sweetest of all sugars.Sweetest of all sugars.

73% as sweet as sucrose73% as sweet as sucrose

Fermented by yeastFermented by yeast

Pyranose form levorotatoryPyranose form levorotatory

Furanose form dextrorotatoryFuranose form dextrorotatory

OccurrenceOccurrence

Occurs in plant kingdom as such OROR

in combination with glucose forming SucroseSucrose

Animal tissues also contain it in small amounts

Hydrolysis of cane sugar and of inulin.

Can be changed to glucose in the liver and so

used in the body.

Main source of energy for the spermatozoa

LevorotatoryLevorotatory (in sucrose dextrorotatorydextrorotatory)

Shows mutarotation

MutarotationMutarotation

Unlike the other stereoisomeric forms, α and β anomers spontaneously interconvert in solution.

This is called mutarotation.

Galactose

Galactose is classified as a:monosaccharide,monosaccharide, an aldosealdose, a hexosehexose, and is a reducing sugarreducing sugar.

Dextrorotatory shows mutarotationDextrorotatory shows mutarotation

Occurrence Occurrence

Galactose is more commonly found in the

disaccharide, lactose or milk sugar.

It is found in seed coat of legumesseed coat of legumes.

32% as sweet as sucrose32% as sweet as sucrose

C-4 epimer C-4 epimer of glucose

Galactose is part of nervous tissues as

galactolipidsgalactolipids

D-mannose

Present in the polysacchride component of

tuberculoproteintuberculoprotein

If ingested, it is absorbed and converted to glucose in

the body

C-2 epimer C-2 epimer of glucose Cannot be differentiated from glucose by

Ozasone testOzasone test

PentosesPentoses Occur widely in animal and plant

kingdom as component of polysacchride

Arabinose and xylose- glycoproteins

Ribose - RNA, ATP, GTP, NAD+,

Coenzymes

Deoxyribose - DNA

Properties Properties

May be aldoses or ketoses

Form ozasone crystals with phenylhadrazinephenylhadrazine

with acids converted to furfuralfurfural,

are strong reducing sugarsare strong reducing sugars

Not fermented by yeast

Deoxy sugars Ribose and its related compound,

deoxyribose, are the building blocks of the backbone chains in nucleic acids, better known as DNA and RNA.

Ribose is used in RNA and deoxyribose is used in DNA.

The presence or absence of the -OH group on

carbon (#2) is an important distinction between

ribose and deoxyribose.

Ribose has an alcohol at carbon # 2, while

deoxyribose does not have the alcohol group.

Deoxyribose give most of sugar reaction but do not form ozasonesDeoxyribose give most of sugar reaction but do not form ozasones

Disaccharides Three common disaccharides: Sucrose — common table sugar = glucose

+ fructose Lactose — major sugar in milk = glucose

+ galactose Maltose — product of starch digestion =

glucose + glucose

The resulting linkage between the sugars is called a glycosidic bond. The molecular formula of each of these disaccharides isC12H22O11 = 2 C6H12O6 − H2O

SucroseSucrose

Sucrose is made from glucose and fructose units

Sucrose or table sugar Cane, beet sugar, Pineapple Has no free anomeric carbon Is a non-reducing sugar No osazone crystals

H O H

H

OHH

OH

CH2OH

H

-D-Glucose

HO CH2OH

HHOH2C

OH H

H HOO

-D-Fructose

O

Dextrorotatory

on hydrolysis becomes levorotary

Invert sugarInvert sugar

Invert sugar 30% more sweet than sucroseInvert sugar 30% more sweet than sucrose

Honey is rich with invert sugar

In sucrase deficiency, malabsorption leads

to diarrhea and flatulence

MaltoseMaltose Glucose+ Glucose Formed in vivo by action of slivary slivary

amylase on starchamylase on starch In vitro formation by acidic hydrolysis of acidic hydrolysis of

starchstarch. Reducing sugar Has free anomeric carbon forms osazone crystals Shows mutarotation 32% as sweet as sucrose32% as sweet as sucrose Baby and invalid foods

LactoseLactose

Glucose + Galactose Milk sugar Reducing sugar In lactase deficiency, malabsorption leads

to diarrhea and flatulence Certain bacteria can ferment lactose to

lactic acid - souring of milk. ( lactobacillus bulgaricus)

16% as sweet as sucrose (least sweet sugar)16% as sweet as sucrose (least sweet sugar)

H O OH

HH

OHH

OH

CH2OH

H

-D-Glucose

HO O

H HH

OHH

OH

CH2OH

H

-D-Galactose

O