4. Function of Carbohydrates
• Abundant dietary source of energy
• Precursors for many organic compound
• Participate in the structure of cell membrane & cellular
functions
• Structural component of many organism
• Also serve as the storage form of energy
10. EPIMERS
• If two monosaccharides differ from each other in the configuration
around a single specific carbon (other than anomeric carbon) atom
they are referred to as Epimers of each other.
• Glucose & galactose are epimers with regard to carbon 4 (C4
epimers) i.e. they differ in the arrangement of –OH group at C 4.
C2 Epimer C4 Epimer
•
D- Mannose D- Glucose D- Galactose
CHO
C
C
C
OH
H
HO H
C
H OH
OH
CH2OH
H
CHO
C
C
C
OH
H
HO H
C
HO H
OH
CH2OH
H
CHO
C
C
C
H
HO H
C
H OH
OH
CH2OH
H
HO
11. EPIMERS
• Glucose & mannose are epimers with regard to carbon 2.(C2
epimers)
• D- Glucose D- Mannose
• The interconversion of epimers is known as Epimerisation or
Epimerism & a group of enzymes namely ‘Epimerases’ catalyze
this reaction
CHO
C
C
C
OH
H
HO H
C
H OH
OH
CH2OH
H
CHO
C
C
C
H
HO H
C
H OH
OH
CH2OH
H
HO
12. Hemiacetal / Hemiketal formation
The hydroxy group of monosaccharides can react with its
own aldehyde or keto functional group to form hemiacetal
/hemiketal
α D- Glucose β- D-Glucose
C
C
C
C
OH
H
HO H
C
H OH
CH2OH
H
O
H OH
C
C
C
C
OH
H
HO H
C
H OH
CH2OH
H
O
HO H
13. • α D- Glucose β- D-Glucose
O
H
OH
OH
H
H
OH
H
OH
CH2OH
H
O
OH
H
OH
H
H
OH
H
OH
CH2OH
H
14. Mutarotation
• Mutaroation: Change in specific rotation on standing
aqueous solution of sugar is known as mutarotation.
• When monosaccharide (glucose) is dissolved in water, its
optical rotation gradually changes until it reaches a
constant value, for eg. Freshly prepared solution of alpha
D-glucose has a specific rotation of +1120 and on standing
specific rotation falls to +52.50 and remains constant at
this value. This final stage can be obtained more quickly
either by heating or by adding some catalyst like acid or
alkali. This change in specific rotation is called as
Mutarotation.
• Fresh solution of beta D-glucose has rotation value of +190
which on standing also changes to +52.50
16. Reaction of monosaccharide
• Tautomerization/ Enolization
The process of shifting a hydrogen atom from one carbon
atom to another in alkaline solution to produce enediols is
known as Tautomerization
D-Glucose Enediol D-Mannose
CHO
C
C
C
OH
H
HO H
C
H OH
OH
CH2OH
H
CHO
C
C
C
H
HO
HO H
C
H OH
OH
CH2OH
H
HC
C
C
C
OH
HO H
C
H OH
OH
CH2OH
H
OH
18. Reducing property of sugars
• Carbohydrates having free & potential
aldehyde / Ketone group are called reducing
sugars They give Fehling’s ,Benedict’s ,
Tommer’s and Osazone test positive
• Eg. Glucose, lactose, maltose, fructose.
CuSO4
Cu2+ Sugar
solution
Cu+
Cupric
Ion
Cuprous
Ion
2Cu(OH) Yellow PPT
Cu2O
Red PPT of cuprous oxide
19. Osazone test
• In these test phenyl hydrazine is reduce to phenyl hydrazone
by sugar solution. Phenyl hydrazone when heated with more
amount of phenyl hydrazine forms yellow crystalline
compound called osazone.
• Glucose, fructose & mannose gives needle shaped crystals
• Maltose gives sunflower shape crystals & lactose gives
powder puff shape crystals.
• Significance:
• Osazone test helps to differentiate reducing sugars from non
reducing sugars like starch, dextrin, sucrose.
• It also helps in differentiating particular type of reducing
sugars.
• It is used to identify and confirm reducing sugars, e.g. glucose,
fructose, galactose, maltose, lactose
21. Oxidation Reaction
• Depending on the oxidizing agent used, the terminal
aldehyde or keto or terminal alcohol or both the groups
may be oxidized.
22. Oxidation
CHO
C
C
C
OH
H
HO H
C
H OH
OH
CH2OH
H
D- Glucose
PtO2 Br2
Nitric acid
COOH
C
C
C
OH
H
HO H
C
H OH
OH
CH2OH
H
COOH
C
C
C
OH
H
HO H
C
H OH
OH
COOH
H
CHO
C
C
C
OH
H
HO H
C
H OH
OH
COOH
H
Glucoronic Acid Gluconic Acid
Glucosaccharic Acid
