chapter 9
Simple Carbohydrates
is a derivative of a ketonanose. It occurs in the
oligosaccharide side chains of some glycoproteins and in
gangliosides, both of which are constituents of cell mem-
branes (Chapter 10).
Sugar Phosphates
Sugar phosphates, which are phosphoric acid esters of
monosaccharides, occur as intermediates in carbohydrate
metabolism. Two of these compounds, namely, ribose
phosphate and deoxyribose phosphate, are constituents
of nucleotides and nucleic acids. Glucose can be phos-
phorylated either at the
primary hydroxyl group to
yield glucose
-phosphate or at the Cj anomeric hydroxyl
group to yield glucose 1-phosphate (Figure 9-16). In
-phosphate, the phosphate group can exist in
either the
or /1-position. These two forms are not
interconverted in solution because the substitution of the
anomeric hydroxyl group by any group prevents the ring
opening responsible for the equilibration of anomers. The
reducing property is also lost.
Another class of sugar phosphates consists of nucle-
oside diphosphate sugars, in which a monosaccharide
is attached through the anomeric hydroxyl group to a
nucleoside diphosphate. A nucleoside contains D-ribose,
an aldopentose, attached to a purine or a pyrimidine base,
as in uridine diphosphate glucose (Figure 9-16). Such
compounds are important in the synthesis of polysaccha-
rides, the interconversion of sugars, and the synthesis of
Deoxy Sugars
In deoxy sugars, one or more hydroxyl groups of the
pyranose or furanose ring is substituted by hydrogen. A
well-known example is
-deoxyribose, which is a com-
ponent of deoxyribonucleotides, the repeating units of de-
oxyribonucleic acids (DNA). Another example is L-fucose
d - R ib o s e -5 - p h o s p h a te
( D -rib o fu ran o sy l-5 -p h o sp h ate)
2-D eoxy- o -rib o se -5 -p h o sp h a te
(2 -d eo x y -D -rib o fu ran o sy l-5 -p h o sp h ate)
D -G iucose-1 -p h o sp h a te
(a-D -g iu co p y ran o sy l p h o sp h ate )
C H 2OPC>3
H O '
)H O H
o -G lu c o se -6 -p h o sp h a te
(6 -p h o sp h o - D -g lucopyranose)
U ridine d ip h o sp h a te g lu c o se
F I G U R E 9 - 1 6
Sugar phosphates and a nucleoside diphosphate sugar. When the anomeric position of a sugar is not substituted, the
configuration at this position is not specified because the sugar can exist in either the
a -
or /
-anomeric form.
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