Carbohydrates

Monosaccharides

Monosaccharides are a type of simple carbohydrate, or simple

sugar.

The word comes from the Greek • Manos = single, sacchar = sugar

Monosaccharides are the simplest carbohydrates in that they cannot be hydrolyzed to smaller carbohydrates.

A monosaccharide is a single ringed carbohydrate

Formula : (CH2O)n • Where n ranges from 3 to 7

elmaxe p

Glucose

Fructose

Ribose

Galactose

Properties

Water soluble sweet

Reducing sugar

Groups

aldehyde

Called aldose

Hydrogen and Oxygen

Glucose Galactose

ketone

Called Ketose

Carbon and Oxygen Fructose

C L A S S I F

I

C

A

T

ION

based on how many carbon atoms they have

3 carbon atoms

• Triose• (CH2O)3

4 carbon atoms

• Tetrose• (CH2O)4

5 carbon atoms

• Pentose• (CH2O)5

6 carbon atoms

• Hexose• (CH2O)6

7 carbon atoms

• Heptose• (CH2O)7

Examples

TriosesGlyceraldehyde

Dihydroxyacetone

Pentoses

ribose

deoxyribose

ribulose

Hexoses

glucose

Fructose

galactose

Combination of these systems

CH2O

CH2O

CH2O CH2Otriose

ketose

aldose

hexose

pentose

tetrose

tetrose

heptose

aldose trioseAldo triose

ketose

hexose

Keto hexose

D and L Notations

The letter D is assigned to the structure with—OH

on the right.

D-glyceraldehyde

The letter L is assigned to the structure with —OH

on the left.

L-glyceraldehyde

O

Chiral carbon

Ribose

aldopentoseReducing Sugar

ribose is used in RNA

deoxyribose is used in DNA

Ribose

An aldohexose

GLUCOSEkey sugar of

the body

Major source of energy for

the cell

Component of disaccharide • Sucrose• Maltose • Lactose

Monomer of polysaccharides• Starch • Cellulose • Glycogen

FRUCTOSEmajor constituent of the polysaccharide insulin

splits sucrose into glucose and fructose

metabolized directly but is also readily converted to glucose in the liver

Known as

levulose

A ketohexose

Mostly

found in

fruits and

vegetables

GALACTOSE

synthesized in the mammary glands

to make the lactose of milk

a constituent of glycolipids and

glycoproteins in many cell membranes such as those in nervous tissue

Aldohexose

Isomer of glucose

can be found most readily in milk and dairy products

R E A C IT O N

Monosaccharides are reducing sugars if their

carbonyl groups oxidize to give carboxylic acids.

� In the Benedict’s text, D-glucose is oxidized to D-

gluconic acid. Glucose is a reducing sugar.

OXIDATION

The reduction of the carbonyl group produces sugar

alcohols, or alditols.

D-Glucose is reduced to D-

glucitol also called sorbitol.

REDUCTION