12
Carbohydrates
12.1 Carbohydrates
Many aspects of the chemistry of carbohydrates are
not specific to this class of compounds, but are
merely examples of the simple chemical reactions
we have already met. Therefore, against usual
practice, we have not attempted a full treatment
of carbohydrate chemistry and biochemistry in this
chapter. We want to avoid giving the impression
that the reactions described here are something
special to this group of compounds. Instead, we
have deliberately used carbohydrates as examples of
reactions in earlier chapters, and you will find suitable
cross-references.
Carbohydrates are among the most abundant
constituents of plants, animals, and microorganisms.
Polymeric carbohydrates function as important food
reserves, and as structural components in cell walls.
Animals and most microorganisms are dependent
upon the carbohydrates produced by plants for their
very existence. Carbohydrates are the first products
formed in photosynthesis, and are the products from
which plants synthesize their own food reserves, as
well as other chemical constituents. These materials
then become the foodstuffs of other organisms. The
main pathways of carbohydrate biosynthesis and
degradation comprise an important component of
intermediary metabolism that is essential for all
organisms (Chapter 15).
The name carbohydrate was introduced because
many of the compounds had the general formula
C x (H 2 O) y , and thus appeared to be hydrates of carbon. The terminology is now commonly used in a
much broader sense to denote polyhydroxy aldehydes
and ketones, and their derivatives. Sugars or saccharides are other terms used in a rather broad sense
to cover carbohydrate materials. Though these words
link directly to compounds with sweetening properties, application of the terms extends considerably
beyond this. A monosaccharide is a carbohydrate
usually in the range C 3 –C 9 , whereas oligosaccharide
covers small polymers comprised of 2–10 monosaccharide units. The term polysaccharide is used for
larger polymers.
12.2 Monosaccharides
Six-carbon sugars (hexoses) and five-carbon sugars
(pentoses) are the most frequently encountered
monosaccharide carbohydrate units in nature. Primary
examples of these two classes are the hexoses glucose
and fructose, and the pentose ribose. Note the suffix
-ose as a general indicator of carbohydrate nature.
Essentials of Organic Chemistry Paul M Dewick
© 2006 John Wiley & Sons, Ltd
Carbohydrates
12.1 Carbohydrates
Many aspects of the chemistry of carbohydrates are
not specific to this class of compounds, but are
merely examples of the simple chemical reactions
we have already met. Therefore, against usual
practice, we have not attempted a full treatment
of carbohydrate chemistry and biochemistry in this
chapter. We want to avoid giving the impression
that the reactions described here are something
special to this group of compounds. Instead, we
have deliberately used carbohydrates as examples of
reactions in earlier chapters, and you will find suitable
cross-references.
Carbohydrates are among the most abundant
constituents of plants, animals, and microorganisms.
Polymeric carbohydrates function as important food
reserves, and as structural components in cell walls.
Animals and most microorganisms are dependent
upon the carbohydrates produced by plants for their
very existence. Carbohydrates are the first products
formed in photosynthesis, and are the products from
which plants synthesize their own food reserves, as
well as other chemical constituents. These materials
then become the foodstuffs of other organisms. The
main pathways of carbohydrate biosynthesis and
degradation comprise an important component of
intermediary metabolism that is essential for all
organisms (Chapter 15).
The name carbohydrate was introduced because
many of the compounds had the general formula
C x (H 2 O) y , and thus appeared to be hydrates of carbon. The terminology is now commonly used in a
much broader sense to denote polyhydroxy aldehydes
and ketones, and their derivatives. Sugars or saccharides are other terms used in a rather broad sense
to cover carbohydrate materials. Though these words
link directly to compounds with sweetening properties, application of the terms extends considerably
beyond this. A monosaccharide is a carbohydrate
usually in the range C 3 –C 9 , whereas oligosaccharide
covers small polymers comprised of 2–10 monosaccharide units. The term polysaccharide is used for
larger polymers.
12.2 Monosaccharides
Six-carbon sugars (hexoses) and five-carbon sugars
(pentoses) are the most frequently encountered
monosaccharide carbohydrate units in nature. Primary
examples of these two classes are the hexoses glucose
and fructose, and the pentose ribose. Note the suffix
-ose as a general indicator of carbohydrate nature.
Essentials of Organic Chemistry Paul M Dewick
© 2006 John Wiley & Sons, Ltd