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Carbohydrates
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Carbohydrates
2.6
Carbohydrates
Carbohydrates are made from CARBON,
HYDROGEN and OXYGEN
FUNCTION 1:They STORE ENERGY in plants and animals
FUNCTION 2:Plant cell walls depend on the STRUCTURAL
role of some carbohydrates
MONOSACCHARIDES
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CARBOHYDRATES
DISACCHARIDES
POLYSACCHARIDES
Monosaccharides
Monosaccharides are small organic molecules used as bulding blocks for more
complex carbohydrates. Click each of the blue boxes to work through the slide.
General Formula
(CH2O)n
So, when
n=3
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When n=5
What does the ‘n’ stand
for?
Number of Carbon atoms
TRIOSE, e.g. glyceraldehyde In metabolic reactions
When n=6
PENTOSE, e.g. ribose –
HEXOSE, e.g. glucose -
formation of nucleic acid
main source of energy
next
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MONOSACCHARIDES
Monosaccharides can exist as straight
chain and ring forms.
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The ring forms are common when
glucose is in solution.
Isomerism in Glucose C6H12O6
Alpha-glucose
CH2OH
Oxygen
Hydrogen
Carbon
Glucose forms two isomers
Hydroxide (OH)
beta-glucose
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CH2OH
Show structural change
They both have the same molecular
formula but a different structure
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Both these molecules are glucose.
Both have a molecular formula of C6H12O6.
But they are structurally different.
Biological role of monosaccharides
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
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As building blocks…..
•Repeated glucose molecules build up; starch &
glycogen
•Ribose (5C) forms part RNA
•Deoxyribose (5C) forms part DNA
Disaccharides
Disaccharides form when two monosaccharide units join forming a
glycosidic bond, by a condensation reaction.
A disaccharide can be made
from two of the same
monosaccharide molecule or
from two different ones.
The combination of
monosaccharides determines
which disaccharide is formed.
MONOSACCHARIDES
DISACCHARIDE
WATER
SUCROSE
MALTOSE
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GLUCOSE
GLUCOSE
GALACTOSE
FRUCTOSE
GLUCOSE
LACTOSE
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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
Milk sugar
Lactose
Forming Disaccharides
Glucose
CH2OH
CH2OH
CH2OH
H
C
OH
C
O
H
OH
H
C
C
H
OH
H
H
C
C
OH
OH
C
O
H
OH
H
C
C
C
H
OH
H
OH
Maltose
CH2OH
H
C
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OH
C
CH2OH
O
H
OH
H
C
C
H
OH
H
H
C
C
OH
OOH
H
H
Glycosidic
Bond
C
O
H
OH
H
C
C
C
H
OH
H
OH
This is a CONDENSATION reaction,
where a water molecule is lost.
Polysaccharides
Polysaccharides are large complex molecules known as
POLYMERS.
What is polymerisation ?
Click the bubble
for the answer
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Polymerisation is the process of
bonding many MONOMERS by
condensation reactions to form one
large molecule.
Return to isomerism of glucose
What is a
monomer?
Monomers are the individual
monosaccharides which join
to form the polysaccharide.
Next
Forming polysaccharides
Glucose
CH2OH
H
C
OH
C
CH2OH
O
H
OH
H
C
C
H
OH
H
H
C
OH
H
C
O
OH
H
C
CH2OH
O
H
OH
H
C
C
H
OH
H
H
C
OH
H
C
O
OH
H
C
CH2OH
O
H
OH
H
C
C
H
OH
H
H
C
OH
H
C
O
OH
H
C
O
H
OH
H
C
C
C
H
OH
H
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In this example, 3 condensation reactions have produced 3 water
molecules to produce the polysaccharide.
A HYDROLYSIS reaction (addition of water) reverses the reaction
and splits the polysaccharide releasing 3 monosaccharide
molecules.
OH
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
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STARCH
CELLULOSE
GLYCOGEN
Starch
•
Made up of two types of
polysaccharide;
1) Amylose 2) Amylopectin
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Amylose
• Condensation reactions
between alpha glucose (14 glycosidic links).
• Forms a coiled helix
Starch
Amylopectin
• Condensation reactions
between alpha glucose (1-4
glycosidic links).
• Branches of 1-6 glycosidic
links also exist.
• Coiled springs with a
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branched structure
formed.
are
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Starch grains are a mixture of amylose & amylopectin
Starch is a polysaccharide
Starch it is a insoluble store of glucose
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It is ideal as a storage molecule because:
• It is compact
• Insoluble
• Has no osmotic effect
• Is readily broken down to mono and disaccharides
Starch is only found in plant cells, the animal
equivalent is called GLYCOGEN.
GLYCOGEN is the storage
polysaccharide in animals
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It has 1-4 glycosidic links
and 1-6 glycosidic links
It is similar to amylopectin but has a greater number
of shorter side branches
Cellulose
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•
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!
Cellulose
It is the hydrogen
bonding between the
straight chains that
helps to give
cellulose it’s
strength.
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Long straight chains
of polysaccharides
linked together by
hydrogen bonds
Hydrogen bonds are formed between the hydroxyl groups
of adjacent parallel chains
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70 chains of β glucose combine to form a
MICROFIBRIL.
Lots of MICROFIBRILS are held together to form
FIBRILS.
Chitin
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• Forms the exoskeletons of insectslightweight 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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You can give this
question a go, in
order to prove your
understanding: