1. Enzymes and the digestive system
2.2 Carbohydrates – monosaccharides
2.3 Carbohydrates - disaccharides
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2. Settler Activity: Can you unscramble these anagrams to give today’s key words?
MERMOON
YELPORM
HANDISOCCERMAO
SHARCCAIDIDE
RIDEPAYOLCHASC
STEENBIC’D SETT
SOCGLUE
Monomer
Polymer
Monosaccharide
Disaccharide
Polysaccharide
Benedict’s test
Glucose

3. Learning Objectives All students should be able...
To understand how large molecules like carbohydrates are constructed.
To describe the properties of a monosaccharide.
To draw the structure of glucose and fructose.
To describe how monosaccharides link together to form disaccharides.
To draw the reaction between two monosaccharides, hence draw the structure of a disaccharide, including labelling the glycosidic bond.
Specification reference: 3.1.2
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4. Success Criteria
I can translate biological prefixes used in naming biological molecules.
I know how monosaccharides form disaccharides and polysaccharides.
I can outline the properties of a monosaccharide.
I can draw glucose and fructose.
I can draw maltose and sucrose and label the glycosidic bond.
I can answer exam questions on disaccharides.
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5. Starter Activity: In biology certain prefixes are commonly used to indicate numbers. Can you match these Greek/Latin terms to their English translation?
Tri
Hexa
Penta
Mono
Poly Di
Tetra
One
Two
Three
Four
Five
Six
Many

6. Life based on carbon
Carbon atoms are unusual in that they readily form bonds with other carbon atoms, allowing a sequence of carbon atoms of various lengths to be built up.
This unusual property allows a huge number of different types and sizes of molecule, all based on carbon.
The variety of life that exists on Earth is a consequence of living organisms being based on the versatile carbon atom. Therefore, carbon-containing molecules are known as organic molecules.
In living organisms, there are relatively few other atoms that attach to carbon. Life is therefore based on a small number of chemical elements.
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7. Activity 1: How many bonds?
Spot the mistake!
Element
No. of bonds
Carbon
Nitrogen
Oxygen
Sulphur
Hydrogen C H H H O H C C O H

8. Making Polymers
Many organic molecules, including carbohydrates, are made up of individual molecules called monomers.
The carbon atoms of these monomers join to form longer chains called polymers Polymers are made up of repeated molecules called monomers.
Biological molecules like carbohydrates and proteins are often polymers.
Most of these polymers are made up of just four elements: carbon hydrogen, oxygen and nitrogen.

9. Carbohydrates
Carbohydrates are carbon molecules (carbo) combined with water (hydrate). Some molecules are small while others are large.
These are all examples of sugars (saccharides).
Where there is only one sugar it is called a monosaccharide.
Two monosaccharides can join together to form a disaccharide.
Many monosaccharide units can join together to form polysaccharides.
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10. Monosaccharides (single sugars)
They all reduce Benedict’s reagent, are sweet-tasting, soluble substances and easily transported, and are the main respiratory substrates. They have the general formula (CH2O)n, where n can be any number from 3 to 7.
where n = 3 it is called a triose sugar
e.g. glyceraldehyde is C3H6O3
where n = 5 it is called a pentose sugar
e.g. ribose is C5H10O5
where n = 6 it is called a hexose sugar
e.g. glucose is C6H12O6
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11. Glucose CH2OH CH2OH O O OH H C H C H H H C C C C OH H OH H H OH OH OH
It is a hexose (6-carbon) sugar and has the formula C6H12O6.
The atoms form a ring.
There are 2 forms of glucose: α glucose β glucose. Can you spot the difference?
CH2OH
CH2OH O O OH H C H C H H H C C C C OH H OH H H OH OH OH C C C C H OH H OH
α glucose
β glucose
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12. Drawing β glucose! Drawing α glucose! CH2OH 6 5 H C O OH H H C C 4 1
Reducing Centre OH H OH H OH C C 2 3 H OH
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13. Drawing α glucose (simplified)!H O H OH OH
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14. Drawing Fructose! O 1 CH2OH 6 CH2OH 2 C C 5 OH OH H H 3 C C 4 H OH
Reducing Centre 3 C C 4 H OH
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15. Disaccharides
Pairs of monosaccharides can be combined to form a disaccharide.
Glucose linked to glucose forms maltose.
Glucose linked to fructose forms sucrose.
Glucose linked to galactose forms lactose.
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16. Condensation Reactions
When monosaccharides join, a molecule of water is removed and the reaction is therefore called a condensation reaction.
The bond that is formed is called a glycosidic bond.
When water is added to a disaccharide under suitable conditions, it breaks the glycosidic bond releasing the constituent monosaccharides. This is called hydrolysis (addition of water that causes breakdown).
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17. Formation of glycosidic bond by removal of water (condensation reaction)
α glucose
α glucose C
CH2OH OH H O 1 2 3 4 5 6 C
CH2OH OH H O 1 2 3 4 5 6
H2O
Water
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18. Formation of glycosidic bond by removal of water (condensation reaction)
CH2OH OH H O 1 2 3 4 5 6 C
CH2OH O OH H 1 2 3 4 5 6
+ H2O
Maltose
Water
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19. Formation of glycosidic bond by removal of water (condensation reaction)
α glucose
fructose C
CH2OH OH H O 1 2 3 4 5 6
CH2OH C OH H O 1 2 3 4 5 6
H2O
Water
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20. Formation of glycosidic bond by removal of water (condensation reaction)
CH2OH 6 5 H C O O H 1
CH2OH 6
CH2OH H C C 4 2 1 C C 5 OH H O OH H H OH C C 3 2 3 C C 4 H OH H OH
Sucrose
+ H2O
Water
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21. Plenary: Answer these questions under exam questions.
Large molecules often contain carbon. Why is this?
What is the general name for a molecule that is made up of many similar repeating units?
Which one, or more, monomer units make up each of the following carbohydrates?
a) lactose
b) sucrose
c) starch
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22. Glucose (C6H12O6) combines with fructose (C6H12O6) to form the disaccharide sucrose. From your knowledge of how disaccharides are formed, work out the formula of sucrose.
To hydrolyse a disaccharide it can be boiled with hydrochloric acid but if hydrolysis is carried out by an enzyme a much lower temperature (40⁰C) is used. Why is this?
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23. Answers Carbon atoms readily link to one another to form a chain.
Polymer
a) glucose + galactose
b) glucose + fructose
c) glucose only
4. C12H22O11 (C6H12O6 + C6H12O H2O)
5. Enzymes are denatured at higher temperatures and this prevents them functioning / enzymes lower the activation energy required.
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24. Learning Objectives All students should be able...
To understand how large molecules like carbohydrates are constructed.
To describe the properties of a monosaccharide.
To draw the structure of glucose and fructose.
To describe how monosaccharides link together to form disaccharides.
To draw the reaction between two monosaccharides, hence draw the structure of a disaccharide, including labelling the glycosidic bond.
Specification reference: 3.1.2
19/09/2018