CARBOHYDRATES

Foundation Module-Phase 1

Department of Biochemistry

Faculty of Medical Sciences

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

Back

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Structure

(Single Sugar Unit)

Monosaccharide

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

C

groupsgroups

1 2 3

4 5 6

Answers

v

Chiral centers

Penultimate OH group

Fisher projectionHaworth projection

Structural representation of sugars

(straight chain representation) (simple ring in perspective)

Fisher projection Haworth projection

DisaccharidesSugars composed of two monosaccharides linked together by glycosidic bonds.

e.g.Maltose

Common Disaccharidessucrose (table sugar)

Commercially obtained from sugar cane or sugar beet

Used : • as a nutrient (malt extract)• as a sweetener • as a fermentative reagent

(1,4) linkage maltose (seed sugar)

Found in germinating grains

lactose (milk sugar)

Refer: What is lactose intolerance?

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

Polysaccharides

(Many sugar units)

Starch

Test for starch?

Answer

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

Cellulose

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

Back to the beginning

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

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1. Barfoed’s test2. Disaccharides3. Monosaccharides

Can have two sets of answers

b) Glucose

(Barfoed’s test is positive for Monosaccharides only)

Back to the question

c) Fructose

(Seliwanof’s test is positive for Keto sugars)

Back to the question

1 2 3

4 5

1

2

3

4

5

N0

Yes

N0

N0

Yes

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