Monosaccharides are simple sugars that serve as building blocks for other carbohydrates. They include pentoses with 5 carbons like ribose and hexoses with 6 carbons like glucose and fructose. Glucose and fructose are isomers with the same formula but different structures. Monosaccharides can exist as linear molecules or in ring forms like furanoses. They undergo various reactions including oxidation, reduction, and fermentation.

1. Monosaccharides (Simple sugars)
• They may exist in a linear molecule or in ring forms.
• They are classified according to the number of carbon
atoms in their molecule.
5 carbons are called pentoses ex. Ribose
6 carbons are called hexoses ex. Glucose
• Many forms exists as isomers. Isomers are molecules
which have the same empirical formula (recipe) but
have different structures (shapes) due to arrangement
of the atoms in the molecule. This also gives them
different properties. Glucose and fructose both have
the empirical formula C6H12O6, but they have different
structural formulas or shapes.
• MONOSACCHARIDES ARE THE BUILDING
BLOCKS FOR ALL OTHER CARBOHYDRATES!

2. Monosaccharides
Aldoses (e.g., glucose) Ketoses (e.g., fructose)
have an aldehyde group at have a keto group, usually
one end. at C2.
H O
C CH2OH
H C OH C O
HO C H HO C H
H C OH H C OH
H C OH H C OH
CH2OH CH2OH
D-glucose D-fructose

3. Trioses
a three-carbon simple sugar.
formed during the metabolic breakdown of hexoses in
muscle metabolism.
Tetroses
are four-carbon sugars.
One tetrose, erythrose, is a intermediate in the hexose
monophosphate shunt for the oxidation of glucose.
Pentoses
are five-carbon sugar molecules.
Ribose and deoxyribose
Ribose forms part of ribonucleic acid (RNA), and
deoxyribose forms part of deoxyribonucleic acid (DNA).

4. D-ribulose
an intermediary in the pentose phosphate shunt
D-lyxose
which is found in heart muscle
D-xylose and D-arabinose
 which are components of glycoproteins.
The Fisher projection representations for the pentoses, are called open-chain
structures. However, the predominant form for pentoses is a ring structures.
Recall that aldehydes react with alcohols to form hemiacetals. In the case of
ribose, the aldehyde can react with the alcohol at carbon number 4 to form two
different compounds.
.

5. The Fischer and Haworth
projection are related as follows:
1) The groups on the right side of the Fisher projection
are written below the plane in the Haworth
projection. Those on the left side are written above
the plane.
2) One exception to rule 1 occurs at carbon 4 in
pentoses and at carbon 5 in hexoses because of the
nature of the creation occurring there. At these
carbons, rule 1 is reversed.
3.) At carbon 1 form is indicated by the –OH being
written below the plane; the form has the –OH
above the plane.
4.) In both projections the CH2OH group, which has
no chiral carbon, is written as a unit.

6. Haworth Projections
◦ aldopentoses also form cyclic hemiacetals
◦ the most prevalent forms of D-ribose and
other pentoses in the biological world are
furanoses
HOCH2 H HOCH2 OH ()
O O
H H H H
H OH () H H
OH OH OH H
-D -Ribofuranose -2-D eoxy-D -ribofuranose
(-D -Rib os e) (-2-D eoxy-D -rib os e)

7. Hemiacetal & hemiketal
formation
H H
An aldehyde
can react with
C O + R' OH R' O C OH
an alcohol to R R
form a aldehyde alcohol hemiacetal
hemiacetal.
R R
A ketone can C O + "R OH "R O C OH
react with an R' R'
alcohol to form ketone alcohol hemiketal
a hemiketal.

8. HEXOSES
The six-carbon sugars.
The most common of all the carbohyrates.
 The most important as far as the human body is concerned
are glucose, galactose and fructose.
The have the same molecular formula but have
diff. structural formulas; they are isomers.

9. 1
CHO
H C OH
2
HO C H
Glucose 3 D-glucose
OH (linear form)
Is an H
4
C
H C OH
aldohexose 5
CH2OH
and can be 6
represented 6 CH2OH 6 CH2OH
5 O 5 O
structurally H
H
H H
H
OH
4 1 4 1
as OH H OH H
OH OH OH H
3 2 3 2
H OH H OH
-D-glucose -D-glucose

10. is known commonly as dextrose, or
grape sugar.
It is a white crystalline solid that is
soluble in water and insoluble in most
organic liquids.
It is found, along with fructose, in
many fruit juices.
It can be prepared by the hydrolysis of
sucrose, a disaccharide, or by the
hydrolysis of starch, polysaccharides.

11. It is normally found in the bloodstream and
in the tissue fluids.
“Metabolism of Carbohydrates,” glucose
requires no digestion and can be given
intravenously to patients who are unable to
take food by mouth.
is found in the urine of patients suffering
from diabetes mellitus and is an indication
of this disease

12. GALACTOSE
 An isomer of glucose, is also an aldohexose.
Glucose and galactose differ from each other
only in the configuration of the H and OH
about a single carbon atom.
Two sugars that differ only in the
configuration about a single carbon atom are
called epimers.
D-Galactose is converted to D-glucose in the
liver by a specific enzyme called an epimerse.
is present in some glycoproteins and
glycolipids.

13. Galactosemia
severe inherited disease, results in the
inability of infants to metabolize galactose
because of a difiency of either the enzyme
galactose 1-phosphate uridyl transferase or
the enzyme galactokinase.
 The galactose concentration increases in
the blood the urine (galactosuria).

14. a-D-galactose
D-galactose

15. FRUCTOSE
can be represented as a straight-chain or as a ring
compound.
The ring structure is predominant. Note that the
ring structure represents a hemiketal.
often called levulose, or fruit sugar and it occurs
naturally in fruit juices and honey.
 It can be prepared by the hydrolysis of sucrose, a
disaccharide, and also by the hydrolysis of insulin,
polysaccharides found in Jerusalem artichokes.
the most soluble and also the sweetest of all sugars,
being 75 percent sweeter than glucose.

16. Fructosemia,
fructose intolerance, is an inherited
disease due to a deficiency of a
deficiency of the enzyme fructose 1-
phosphate aldolase. An infant suffering
from this disease experiences
hypoglycemia, vomiting, and severe
malnutrition. Such a condition is treated
by placing the infant on a low-fructose
diet.

17. a-D-fructose

18. Reactions of the Hexoses
Hexoses, which are either aldoses or ketoses, show reducing properties.
This reducing property is the basis of the test sugar in the urine and in
the blood.
When a reducing agent is treated with an oxidizing agent such as Cu2+
complex, a red-orange precipitate of copper(I) oxide(Cu2O) is formed
heat
aldehyde + Cu2+ acid + Cu2O +
water NaOH
deep blue red-orange
solution precipitate
In this reaction the aldehyde is oxidized to the corresponding acid.

19. When glucose is treated with Cu2+ complex ion and the
mixture is heated, the reaction is as follows:
heat
Cu2+
+ Cu2O +
NaOH
Copper(II) Copper(I)
Complex ion oxide
(deep-blue color) (red-orange
D-glucose precipitate) D-gluconic
acid

20. Benedict's Reagent
O O
RCH + 2Cu2+ + 5HO– RCO– + Cu2O + 3H2O
• Benedict's reagent is a solution of the citrate complex
of CuSO4 in water. It is used as a test for "reducing
sugars." Cu2+ is a weak oxidizing agent.
• A reducing sugar is one which has an aldehyde
function, or is in equilibrium with one that does.
• A positive test is the formation of a red precipitate of
Cu2O.

21. Examples of
Reducing Sugars
• Aldoses: because they have an
aldehyde function in their open-chain
form.
• Ketoses: because enolization
establishes an equilibrium with an
CH OH
2 CHOH CH O
aldose.
C O C OH CHOH
R R R
oxidized by Cu2+

22. Oxidation
If the aldehyde end of the molecule is oxidized,
the product is named and –onic acid. When the
aldehyde end of glucose is oxidized, the product is
called gluconic acid.
If the alcohol at the end opposite the aldehyde is
oxidized, the product is called a –uronic acid. The
ooxidation of the alcohol end of glucose yields
glucuronic acid.
If both ends of the glucose molecule are oxidized
at the same time, the product is called saccaharic
acid.

23. Gluconic acid Glucuronic acid
Saccharic acid

24. REDUCTION
When glucose is reduced, sorbitol is
formed. Sorbitol accumulation in the eyes
is a major factor in the formation of
cataracts due to diabetes.
Reduction of galactose yields dulcitol.
Reduction of fructose yields a mixture of
mannitol and sorbitol.
Mannitol
Used in the treatment of malignant brain
tumors.a

25. FERMENTATION
Glucose ferments in the presence of yeast, forming ethyl
alcohol and carbon dioxide. This reaction will not readily
occur in the absence of yeast. Yeast contains certain
enzymes that catalyze this particular reaction.
enzymes
+
Glucose ethyl alcohol
Fructose will also ferment; galactose will not readily ferment.
Pentoses do not ferement in the presence of yeast

26. Fermentation of Phosphate
Esters
Phosphate esters such as D-glyceraldehyde 3-
phosphate and dihydroxyacetone phosphate esters
involved in glycolysis.

27. Amino sugars
D-glucosamine
An amino group in place of an –OH group.
These amino sugars have been found in
nature.