Transcript Enzymes and the digestive system - VBIOLOGY

Enzymes and the digestive
system
2.2 Carbohydrates – monosaccharides
2.3 Carbohydrates - disaccharides
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Settler Activity: Can you unscramble these
anagrams to give today’s key words?
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MERMOON
YELPORM
HANDISOCCERMAO
SHARCCAIDIDE
RIDEPAYOLCHASC
STEENBIC’D SETT
SOCGLUE
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Monomer
Polymer
Monosaccharide
Disaccharide
Polysaccharide
Benedict’s test
Glucose
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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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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Starter Activity: In biology certain prefixes are
commonly used to indicate numbers. Can you
match these Greek/Latin terms to their English
translation?
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Tri
Hexa
Penta
Mono
Poly
Di
Tetra
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One
Two
Three
Four
Five
Six
Many
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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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Activity 1: How many bonds?
Element
Carbon
Nitrogen
Oxygen
Sulphur
Hydrogen
No. of bonds
Spot the
mistake!
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.
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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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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Glucose
• 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
O
C
H
H
H
C
C
OH
H
OH C
OH
C
H
OH
α glucose
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CH2OH
O
OH
C
H
H
C
C
OH
H
H
OH C
C
H
OH
β glucose
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Drawing β
α glucose!
H
4C
OH
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6 CH2OH
5C
O
OH
H
C3
H
C2
C 1 Reducing
H
OH
H
OH
Centre
OH
H
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Drawing α glucose (simplified)!
H
OH
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O
H
OH
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Drawing Fructose!
O
1 CH2OH
6 CH2OH
C5
2C
OH
Reducing
Centre
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OH
H
3C
C 4
H
OH
H
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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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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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Formation of glycosidic bond by removal of
water (condensation reaction)
α glucose
α glucose
6 CH2OH
6 CH2OH
H
4C
OH
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5C
O
H
OH
H
C3
C2
H
OH
H
H
C1
OH
4C
OH
H 2O
5C
O
H
OH
H
C3
C2
H
OH
Water
H
C1
OH
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Formation of glycosidic bond by removal of
water (condensation reaction)
1-4 Glycosidic bond
6 CH2OH
6 CH2OH
H
4C
OH
5C
O
H
OH
H
C3
C2
H
OH
Maltose
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H
H
4C
C1
O
5C
O
H
OH
H
C3
C2
H
OH
H
C1
OH
+ H2O Water
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Formation of glycosidic bond by removal of
water (condensation reaction)
α glucose
fructose
6 CH2OH
H
4C
OH
5C
O
H
OH
H
C3
C2
H
H
1CH2OH
C1
2C
OH
OH
OH
H 2O
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6CH2OH
C5
OH
3C
H
H
H
C4
OH
Water
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Formation of glycosidic bond by removal of
water (condensation reaction)
6 CH2OH
H
4C
OH
5C
H
OH
O
H
C3
C2
H
OH
Sucrose
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1-2 Glycosidic bond
H
1CH2OH
C1
2C
O
O
6CH2OH
C5
OH
3C
H
H
H
C4
OH
+ H2O Water
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Plenary: Answer these questions
under exam questions.
1. Large molecules often contain carbon. Why
is this?
2. What is the general name for a molecule that
is made up of many similar repeating units?
3. Which one, or more, monomer units make
up each of the following carbohydrates?
a) lactose
b) sucrose
c) starch
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4. 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.
5. 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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Answers
1. Carbon atoms readily link to one another to
form a chain.
2. Polymer
3. a) glucose + galactose
b) glucose + fructose
c) glucose only
4. C12H22O11 (C6H12O6 + C6H12O6 - H2O)
5. Enzymes are denatured at higher temperatures
and this prevents them functioning / enzymes
lower the activation energy required.
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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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