Carbohydrates- 2010

8/7/2019 Carbohydrates- 2010

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Grade 10-

Carbohydratesnotes-

Monosaccharid

es

Disaccharides

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Polysaccharide

s(2010-2011)

Carbohydrates

Characteristics

a. Carbohydrates contain the three elements1.Carbon

2.Hydrogen

3.Oxygen

b. The second half of the name comes from the fact

that hydrogen and oxygen atoms are present in the

ratio of 2:1 as they are in water (hydrates refers to

water ).

c. The general formula for a carbohydrate can be

written as Cx(H2O)y

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Carbohydrates are divided into three main groups:

1. Monosaccharides

2. Disaccharides3. Polysaccharides

Monosaccharides

Characteristics

1. They are sugars .

2. They dissolve easily in water to form sweetsolutions .

3. They have the general formula (CH2O)n .

4. Consist of single sugar molecule (mono means

one).

According to the number of carbon atoms the

Monosaccharides have types :

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Q: So what makes the difference between the

galactose, glucose and fructose?

A: The Structural formula

The molecular and structural formulae:

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For any molecule or substance there is a structural

and molecular formula

a)the molecular formula: it shows the number and

kinds of atoms in a molecule

eg. C6H12O6, H2O

b)Structural formula: in which atoms are shown in

relation to each other, and bonds are shown, so it is

the formula that shows the arrangement of the

atoms including the bonds.

We will study the structure of glucose only, But in

the following diagram we will show you the structural

formulae of glucose, fructose, and galactose and

note the difference although all they have the same

molecular formula which is Molecular Formula:

C6H12O6

Structural formula:

glucose fructose galactose

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The structural formula for glucose

Ring structures:

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Glucose : the form of glucose where the OH group

on carbon number 1 is below the plane of the ring.

Glucose

glucose: the form of glucose where the OH group

on carbon number 1 is above the plane of the ring.

glucose

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Lesson - Disaccharides and the glycosidic

bond

Two monosaccharides are joined together by process

known as Condensation.

Condensation: is a chemical reaction in which two

molecules combine to form one single molecule, together

with the loss of a small molecule. If the small molecule is

water, it is known as a dehydration reaction.

The formation of the disaccharide:

Two hydroxyl (-OH) groups line up alongside each

other. One -OH combines with a hydrogen atom

from the other to form a water molecule. This

allows an oxygen bridge to form between the two

molecules, holding them together and forming a

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http://en.wikipedia.org/wiki/Chemical_reactionhttp://en.wikipedia.org/wiki/Moleculehttp://en.wikipedia.org/wiki/Dehydration_reactionhttp://en.wikipedia.org/wiki/Chemical_reactionhttp://en.wikipedia.org/wiki/Moleculehttp://en.wikipedia.org/wiki/Dehydration_reaction


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http://www3.interscience.wiley.com:8100/legac

y/college/pruitt/0471473219/bioinquiries/appb/f

lash/animation3.html

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http://www3.interscience.wiley.com:8100/legacy/college/pruitt/0471473219/bioinquiries/appb/flash/animation3.htmlhttp://www3.interscience.wiley.com:8100/legacy/college/pruitt/0471473219/bioinquiries/appb/flash/animation3.htmlhttp://www3.interscience.wiley.com:8100/legacy/college/pruitt/0471473219/bioinquiries/appb/flash/animation3.htmlhttp://www3.interscience.wiley.com:8100/legacy/college/pruitt/0471473219/bioinquiries/appb/flash/animation3.htmlhttp://www3.interscience.wiley.com:8100/legacy/college/pruitt/0471473219/bioinquiries/appb/flash/animation3.htmlhttp://www3.interscience.wiley.com:8100/legacy/college/pruitt/0471473219/bioinquiries/appb/flash/animation3.html


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Examples of disaccharides:

Disaccharide Building block(monosaccharides)1.Lactose Glucose +galactose2. sucrose Glucose+ fructose3. Maltose Glucose+ glucose

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Lesson

Polysaccharides

Characteristics:

1. Polysaccharides are polymers whose subunits

are monosaccharides. They are made by joining

many monosaccharides molecules by

condensation.

2. They are not sugars.

Glucose is the most important carbohydrate fuelin human cells. The small size and solubility inwater of glucose molecules allows them to passthrough the cell membrane into the cell. Energyis released when the molecules are metabolised.

(C6H12O6 + 6O2 6CO2 + 6H2O).

Disaccharides are soluble in water, but they aretoo big to pass through the cell membrane bydiffusion. They are broken down in the smallintestine during digestion to give the smallermonosaccharides that pass into the blood andthrough cell membranes into cells.

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C12H22O11 + H2O C6H12O6 + C6H12O6

Monosaccharides are used very quickly by cells.However, a cell may not need all the energy

immediately and it may need to store it. Monosaccharides are converted into

disaccharides in the cell by condensationreactions.

Further condensation reactions result in theformation ofpolysaccharides. These are giantmolecules which, importantly, are too big toescape from the cell. These are broken down by

hydrolysis into monosaccharides when energy isneeded by the cell.

Glucose is the main source of energy for cells, it

is important for living organisms to store it in

appropriate form.

Problems associated with storage ofglucose-

If glucose itself accumulated in cells, it would

dissolve and make the contents of the cell too

concentrated, which would seriously affect its

osmotic properties.

It is also a reactive molecule and wouldinterfere with normal cell chemistry.

These problems are avoided by converting it,

by condensation reaction, to a storage

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polysaccharide which is a convenient,

compact, inert, and insoluble molecule.

This is in the form of starch in plants and

glycogen in animals.

Starch and glycogen

Starch is a mixture of two substances

a) Amylose

b) Amylopectin

Amylose Amylopectin1. Made of many -

glucose molecules.1. Made of many 1,4

linked -glucose

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2. long, unbranching chainof several thousand 1,4linked glucosemolecules

3. The chains are curvedand coil up into helicalstructures like springs.

molecules .2. The chains are shorter

than amylose andbranched. The branches

are formed by 1,6linkages.

DIAGRAM FROM BOOKLET-PG 7-FIG2.5 DIAGRAM FROM BOOKLET-

PG 7- 2.6a

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Amylose

Starch is found in:

1.Chloroplast

2. storage organs such as potato tubers and seeds of

cereals and legumes.

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Cellulose

Characteristics:

1.The most abundant organic molecule on the planet

due to its presence in plant cell walls and its slow rate

of breakdown in nature.

2. Mechanically strong molecule.

3. Cellulose fibers have very high tensile strength.

4. Provide support and strength for plants (rigidity) .

5. Cellulose fibers determine the shape of the plant

cell.

6. Polymer of -glucose.

Between 60-70 cellulose molecules become tightly

cross- linked to form bundles called microfibrils.

Microfibrils are in turn held together in bundles called

fibers by hydrogen bonding. A cell wall has several

layers of fibers running in different directions toincrease strength.

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Carbohydrates- 2010

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