This document discusses several topics relating to biochemistry: 1) Carboxylates are acidic sugar derivatives that are ionized at pH 7. Sugar phosphates are important intermediates in carbohydrate synthesis and metabolism that trap sugars in cells and activate them for chemical reactions. 2) Alditols are reduced forms of aldoses and ketoses with the suffix -itol added, and examples include ribitol, xylitol, and glycerol. 3) Monosaccharides act as reducing agents that can be oxidized, forming enediols and aldonic acids, which is the basis of Fehling's reaction to detect reducing sugars. 4) The modern method of measuring blood glucose

1. Course Title: General Biochemistry
Alditols
Carboxylates
Sugar Phosphates
Monosaccharides Are Reducing Agents
Modern Method of Measuring Blood Glucose Level

3. Carboxylates
The carboxylic acid groups of the acidic sugar derivatives are ionized at pH 7, and the
compounds are therefore correctly named as the carboxylates, e.g., glucuronate, galacturonate,
and so forth.

4. Sugar Phosphates
In the synthesis and metabolism of carbohydrates, mostly the intermediates
are not the sugars themselves but their phosphorylated derivatives.
Condensation of phosphoric acid with one of the hydroxyl groups of a sugar
forms a phosphate ester, as in glucose 6-phosphate.

6. Characteristics
Sugar phosphates are relatively stable at neutral pH and bear a negative charge.
One effect of sugar phosphorylation within cells is to trap the sugar inside the
cell; most cells do not have plasma membrane transporters for phosphorylated
sugars.
Phosphorylation also activates sugars for subsequent chemical transformation.
Several important phosphorylated derivatives of sugars are components of
nucleotides.

7. Alditols
Aldoses and ketoses can be reduced under mild conditions, for example, by
treatment with NaBH4 , to yield polyhydroxy alcohols known as alditols which
are named by adding he suffix- “itol” to the root name of the parent aldose.
CH2OH
C OH
H
C
Ribitol
(from Ribose)
C
CH2OH
OH
OH
H
H
CH2OH
C OH
H
C
Xylitol
(from Xylose)
C
CH2OH
H
OH
H
HO CH2OH
C OH
H
CH2OH
Glycerol
(from Glyceraldehyde)

8. Occurrence
 Ribitol is a component of flavin coenzyme.
 Xylitol is a sweetener that is used in sugarless gum and candies.
 Glycerol is important lipid component.
Monosaccharides Are Reducing Agents
Monosaccharides can be oxidized by relatively mild oxidizing agents such
as cupric (Cu2+) or ferric (Fe+3) ion. The carbonyl carbon is oxidized to a
carboxyl group.

10. Glucose and other sugars capable of reducing cupric ion are called
reducing sugars. They form enediols, which are converted to aldonic acids and
then to a complex mixture of 2-, 3-, 4-, and 6-carbon acids.
This is the basis of Fehling's reaction, a qualitative test for the presence of
reducing sugar. By measuring the amount of oxidizing agent reduced by a
solution of a sugar, it is also possible to estimate the concentration of that sugar.
For many years this test was used to detect and measure elevated glucose levels
in blood and urine in the diagnosis of diabetes mellitus.

11. Modern Method of Measuring Blood Glucose Level
The modern method of measuring blood glucose level is more sensitive and
requires just one drop of blood. This drop of blood is applied to a test strip
containing the enzyme glucose oxidase. The enzyme glucose oxidase coverts D-
glucose in the presence of oxygen to D-glucono-δ-lactone and hydrogen peroxide
(H2O2). A second enzyme, a peroxidase, catalyzes the reaction of the H2O2 with a
colorless compound to produce a colored product, which is measured
spectrophotometrically.