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16.1 Types of Carbohydrates

16.2 Classification of Monosaccharides16.3 D and L Notations from Fischer

Projections16.4 Structures of Some Important

Monosaccharides

Chapter 16 Carbohydrates

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Carbohydrates

Carbohydrates are: A major source of energy

from our diet. Composed of the elements

C, H and O. Also called saccharides,

which means “sugars.” Produced by photosynthesis

in plants.

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Photosynthesis and Respiration

Photosynthesis in plants requires CO2, H2O, and energy from the sun and produces carbohydrates, such as glucose [C6H12O6 =C(H2O)6].

In respiration, glucose is oxidized in living cells to produce CO2, H2O, and energy.

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Types of Carbohydrates Monosaccharides are the simplest carbohydrates. Disaccharides consist of two monosaccharides. Polysaccharides contain many monosaccharides.

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Classification of Monosaccharides Aldoses are monosaccharides with an aldehyde

group and many hydroxyl (-OH) groups. Ketoses are monosaccharides with a ketone group

and many hydroxyl (-OH) groups.

Aldose Aldose Ketose

CHO

HO H

CH2OH

CHO

HO H

OHH

CH2OH

CH2OH

O

HHO

OHH

OH H

OH

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Monosaccharides Monosaccharides are also classified according

to the number of carbon atoms. A triose has three carbons; a tetrose has four

carbons; a pentose has five carbons; and a hexose has six carbons.

triose tetrose hexose

CHO

HO H

CH2OH

CHO

HO H

OHH

CH2OH

CH2OH

O

HHO

OHH

OH H

OH

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Fischer Projections

A Fischer projection Is used to represent carbohydrates. Places the most oxidized group at the top. Uses horizontal lines for bonds that come forward. Uses vertical lines for bonds that go back.

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D and L Notations By convention, the letter L is assigned to the

structure with the —OH on the left. The letter D is assigned to the structure with

—OH on the right.

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D and L Monosaccharides The —OH on the chiral atom farthest from

the carbonyl group is used to assign the D or L configuration.

L-Galactose

C

HO H

OHH

OHH

HHO

CH2OH

O

OHC

H OH

HHO

OHH

OHH

CH2OH

O

D-Glucose

H

CHO

H OH

OHH

OHH

CH2OH

D-Ribose

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D-GlucoseD-Glucose is: Found in fruits, corn syrup, and honey. An aldohexose with the formula C6H12O6. Known as blood sugar in the body.

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Blood Glucose Level

In the body, glucose has a normal concentration of 70-90 mg/dL.

In a glucose tolerance test, blood glucose is measured for several hours after ingesting glucose.

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D-Fructose

D-Fructose: Is a ketohexose

C6H12O6. Is the sweetest

carbohydrate. Is found in fruit

juices and honey. Converts to glucose

in the body.

D-Fructose

CH2OH

C

C

O

C

H

OHH

HO

C

CH2OH

OHH

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D-Galactose

D-Galactose: Is not found free in

nature. Is obtained from lactose,

a disaccharide. Is important in cellular

membranes.

CHO

C

C

OH

C

H

HHO

HO

C

CH2OH

OHH

H

D-Galactose