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Carbohydrates
2.6
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CarbohydratesCarbohydrates are made from CARBON, HYDROGEN and OXYGEN
FUNCTION 2:Plant cell walls depend on the STRUCTURAL role of some carbohydrates
FUNCTION 1:They STORE ENERGY in plants and animals
MONOSACCHARIDES
CARBOHYDRATES
POLYSACCHARIDESDISACCHARIDES
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(CH2O)n
MonosaccharidesMonosaccharides are small organic molecules used as bulding blocks for more complex carbohydrates. Click each of the blue boxes to work through the slide.
General FormulaWhat does the ‘n’
stand for?
Number of Carbon atoms
So, when n=3TRIOSE, e.g. glyceraldehyde -
In metabolic reactions
When n=5 When n=6
HEXOSE, e.g. glucose -
main source of energy
PENTOSE, e.g. ribose –
formation of nucleic acidnextnext
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sMONOSACCHARIDES
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Monosaccharides can exist as straight chain and ring forms.
The ring forms are common when glucose is in solution.
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sIsomerism in Glucose C6H12O6
CHCH22OHOH
CHCH22OHOH
Alpha-glucose
beta-glucose
Show structural changeShow structural change
Oxygen
Hydrogen
Carbon
Hydroxide (OH)
Glucose forms two isomers
They both have the same molecular formula but a different structure
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s Both these molecules are glucose.
Both have a molecular formula of C6H12O6.
But they are structurally different.
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As an energy source…..
•A large amount of energy is stored between the C-H bonds•This is released to form ATP•ATP is the energy currency of the cell
As building blocks…..
•Repeated glucose molecules build up; starch & glycogen•Ribose (5C) forms part RNA•Deoxyribose (5C) forms part DNA
Biological role of monosaccharides
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GLUCOSE
MALTOSESUCROSE
GLUCOSE
GLUCOSE
Disaccharides
A disaccharide can be made from two of the same
monosaccharide molecule or from two different ones.
Disaccharides form when two monosaccharide units join forming a
glycosidic bond, by a condensation reaction.
The combination of monosaccharides determines which disaccharide is formed.
MONOSACCHARIDES DISACCHARIDE
FRUCTOSEGALACTOSE
WATERWATERWATER
LACTOSE
GLUCOSE
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Most common disaccharides
Monosaccharide Disaccharide Found in !
Glucose and glucose Maltose Malt sugar
Glucose and fructose Sucrose Cane sugar
Glucose and galactose
Lactose Milk sugar
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OOHOH
Forming Disaccharides
C C
C
C O
C
H
OH
OHOH
OH
HH
CH2OH
H
H
CHCH22OHOH
C C
C
C O
C
H
OH
OHOH
OH
HH
CH2OH
H
H
C C
C
C O
C
H
OH
OH
OH
HH
CH2OH
H
H
C C
C
C O
C
H
OH
OH
OH
HH
CH2OH
H
H O
H H
GlycosidicBond This is a
CONDENSATION reaction, where a water molecule is lost.
Glucose
Maltose
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sPolysaccharides
Polysaccharides are large complex molecules known as
POLYMERS.
Monomers are the individual monosaccharides which join to form the polysaccharide.
Polymerisation is the process of bonding many MONOMERS by condensation reactions to form one large molecule.
Return to isomerism of glucoseReturn to isomerism of glucoseNextNext
What is polymerisation
?
What is a monomer?
Click the bubble for the answer
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OOHOH
Forming polysaccharides
C C
C
C O
C
H
OH
OH
HH
CH2OH
H
H
C C
C
C O
C
H
OH
OH
OH
HH
CH2OH
H
H
O
H H
In this example, 3 condensation reactions have produced 3 water molecules to produce the polysaccharide.
O
H H
C C
C
C O
C
H
OH
OH
OH
HH
CH2OH
H
H
C C
C
C O
C
H
OH
OH
HH
CH2OH
H
H
OHOH OHOH
Glucose
O
O
H H
O
A HYDROLYSIS reaction (addition of water) reverses the reaction and splits the polysaccharide releasing 3 monosaccharide molecules.
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Polysaccharides• Polymers with subunits of monosaccharides• Repeated condensation reactions• Normally 1000’s of monomers • Polysaccharides are not sugars• Polysaccharides are insoluble• They are used for storage or construction
STARCH CELLULOSE GLYCOGEN
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sStarch
• Made up of two types of polysaccharide;
1) Amylose 2) Amylopectin
Amylose• Condensation reactions
between alpha glucose (1-4 glycosidic links).
• Forms a coiled helix
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sStarch
Amylopectin• Condensation reactions
between alpha glucose (1-4 glycosidic links).
• Branches of 1-6 glycosidic links also exist.
• Coiled springs with a
branched structure are formed.
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sStarch grains are a mixture of amylose & amylopectin
Starch is a polysaccharide
Starch it is a insoluble store of glucose
Starch is only found in plant cells, the animal equivalent is called GLYCOGEN.
It is ideal as a storage molecule because:• It is compact• Insoluble • Has no osmotic effect• Is readily broken down to mono and disaccharides
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sGLYCOGEN is the storage polysaccharide in animals
It has 1-4 glycosidic links
and 1-6 glycosidic linksIt is similar to amylopectin but has a greater number of shorter side branches
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sCellulose
• C1-4 links make up this polysaccharide.
• If C1 and C4 are to react, one glucose molecule needs to flip through 180o.
• It is this subtle difference that make cellulose so strong!
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Cellulose
Long straight chains of polysaccharideslinked together by hydrogen bonds
It is the hydrogen bonding between the straight chains that helps to give cellulose it’s strength.
Hydrogen bonds are formed between the hydroxyl groups of adjacent parallel chains
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s 70 chains of β glucose combine to form a MICROFIBRIL.
Lots of MICROFIBRILS are held together to form FIBRILS.
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Chitin• Forms the exoskeletons of insects-
lightweight and waterproof• Similar to cellulose but also has amino
acids to form a mucopolysaccharide• The OH groups are replaced by amino
acids
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sYou can give this question a go, in order to prove your understanding:
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