Page 97 - The Manga Guide to Biochemistry

5. Types of Monosaccharides

Aldoses and Ketoses

We already saw that one of the basic forms of a saccharide (monosaccharide) has its first

carbon forming an aldehyde group (see page 61 for more details). Another form of mono-

saccharide has its second carbon forming a ketone group.

Monosaccharides that have an aldehyde group are called aldoses, and monosaccharides

with a ketone group are called ketoses.

Some examples of aldoses are glucose and galactose, and the most well-known ketose

is fructose. (For more details about fructose, see Chapter 3.)

HO aldehyde CH2OH ketone
C group CO group

H C OH HO C H

HO C H H C OH

H C OH

H C OH H C OH

CH2OH CH2OH

Glucose Fructose
(an Aldose) (a ketose)

Pyranose and furanose

Earlier we learned that when certain monosaccharides, like glucose, take a cyclic structure,
they resemble a hexagon. A monosaccharide that takes this form of a six-membered ring,

made up of five carbons and one oxygen, is called a pyranose. However, there are some

cases in which a monosaccharide will resemble a pentagon, made up of four carbons and

one oxygen. This is called a furanose.

Although glucose normally takes the form of pyranose, in extremely rare cases it
becomes furanose. To distinguish the two, the former is called glucopyranose, and the latter

is called glucofuranose.

Fructose can also become a pyranose or furanose when it takes a cyclic structure, and
these forms are called fructopyranose and fructofuranose, respectively.

CH2OH CH2OH
HOCH
HH O O
H H

HO OH H OH H OH H OH
H OH
H OH
glucopyranose
Glucofuranose

Photosynthesis and Respiration 83