CARBOHYDRATES Foundation Module-Phase 1 Department of Biochemistry Faculty of Medical Sciences
Dec 14, 2015
What are carbohydrates?
Energy
•Aldehyde or ketone derivatives of polyhydric alcohol
•Formula (CH2O)n (n > 3)
•Not all carbohydrates have this empirical formula:
deoxysugars, aminosugars
•used as an energy source and in making cell
structures.
Sources of carbohydrate
Rice
Wheat
Bread
Biscuit
Potato Oats
Do you know….
• Q1: List the main functions of carbohydrates?
• Q2: How are carbohydrates classified?
Answer
Answer
Types of Carbohydrates
• Based on the number of monomers.
1. Monosaccharides: 1
2. Disaccharides: 2
3. Oligosaccharides: 3-20
4. Polysaccharides: more than 20
Back
Q3: How to classify monosaccharides?
– According to the number of carbons
– According to functional groups • Aldosugars• Ketosugars
Common Monosaccharides
fructose (fruit sugar) galactos
e
How to measure Glucose
For your interest only
Properties of monosaccharides?
A. Physical properties
* Highly soluble in water
* Most taste sweet
B. Chemical properties
* Formation of cyclic hemiacetals or hemiketals
* New chiral center => 2 “anomers”
designated and
Fisher projectionHaworth projection
Structural representation of sugars
(straight chain representation) (simple ring in perspective)
DisaccharidesSugars composed of two monosaccharides linked together by glycosidic bonds.
e.g.Maltose
Used : • as a nutrient (malt extract)• as a sweetener • as a fermentative reagent
(1,4) linkage maltose (seed sugar)
Found in germinating grains
Polysaccharides or glycans Complex carbohydrates that are made up of hundreds of
monosaccharides linked by glycosidic bonds.
Homoglycans
•Starch•Cellulose•Glycogen •Inulin
Heteroglycans
•Gums•Mucopolysaccharides
Suspensions of amylosein water adopt a helical conformation.
Iodine (I2) can insert inthe middle of the amylosehelix to give a blue colorthat is characteristic anddiagnostic for starch.
Identification of starch-Iodine test
Back to question
X
Control Test
Following is the test results for 3 different sugars
1. Name the test
2. What is in X & Z?
3. What is in Y ? Answer
Y
Barfoed’s testFollowing is the Barfoed’s test results for sugars.
YX
Tube Y contains ………..
a) Maltose
b) Glucose
c) LactoseAnswer
Seliwanoff’s testFollowing is the Seliwanoff’s test results for sugars.
X Y
Tube Y contains……….
a) Glucose
b) Maltose
c) Fructose Answer
Q1- List the main function of carbohydrates
• Sources of energy
• Form structural components– cellulose, lignin, murein
• Molecular recognition– Blood group antigens
• Associated with other entities – DNA, RNA, glycosides, vitamins
Back to the question
Q3:How to classify carbohydrates?
• Number of monomers• Monosaccharides(1)• Disaccharides(2)• Oligosacchrides(2-10)• Polysaccharides or glycans(>10)
– Homopolysaccharides– Heteropolysaccharides– Complex carbohydrates
Glucose measurement methods
• Most are enzymatic methods
– 3 enzyme systems are currently used :
• Glucose oxidase
• Glucose dehydrogenase
• Hexokinase
-D-glucose + O2
glucose oxidaseD-gluconolactone + H2O2
D-gluconolactone + H2O gluconic acid
H2O2 + chromogenic oxygen acceptor (ortho-dianisidine, 4 aminophenazone, ortho-tolidine)
peroxidase
colored chromogen + H2O
Glucose oxidase methods:colorimetric method
A blood test for glucose levels
H
C
CH2OH
O
H OH
HO H
H OH
H OH
C
CH2OH
O
H OH
HO H
H OH
H OH
OH
D-Gluconic Acid(An Aldonic Acid)
D-Glucose
Glucose Oxidase
O2 H2O2
Dye Colored Dye
Back to the question
Answer
1. Benedict’s test
2. Reducing sugar
3. Non reducing sugar
Back
1. Barfoed’s test2. Disaccharides3. Monosaccharides
Can have two sets of answers