Cell metabolism
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Contents
Metabolism
Enzymes
Role of enzymes in
• plants and animals
• metabolism
Enzymes involved in
chemical breakdown
Experiments
Immobilised enzymes
• What are they?
• Methods of
immobilisation
• Advantages
• Uses
Active Site
Specificity
Effect of pH on
enzyme action
Effect of temperature
on enzyme action
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Metabolism
is the totality of chemical reactions that take
place in an organism
Anabolism = Reactions which join smaller
molecules to make larger ones e.g.
Catabolism = Reactions which break down big
molecules e.g.
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Sources of Energy
Solar energy – sunlight is a source of energy
capable of being absorbed by cellular
pigments e.g. chlorophyll.
Cellular energy – cell sources of energy capable
of release by metabolic processes in cells e.g.
heat given off from germinating peas.
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Enzymes
Highly specific,
organic,
protein catalysts
that work very rapidly in
both directions
and are affected by
heat,
pH,
radiation,
substrate and product
concentration and
the presence or absence
of co-factors and/or
inhibitors.
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Enzyme - definition
Highly specific, organic, protein, catalysts that
work very rapidly in both directions and are
affected by heat, pH, radiation, substrate
and product concentration and the
presence or absence of co-factors and/or
inhibitors.
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Enzyme - definition
Highly specific, organic, protein, catalysts that
work very rapidly in both directions and are
affected by heat, pH, radiation, substrate
and product concentration and the
presence or absence of co-factors and/or
inhibitors.
7
Enzyme - definition
Highly specific, organic, protein, catalysts that
work very rapidly in both directions and are
affected by heat, pH, radiation, substrate
and product concentration and the
presence or absence of co-factors and/or
inhibitors.
8
Enzyme - definition
Highly specific, organic, protein, catalysts that
work very rapidly in both directions and are
affected by heat, pH, radiation, substrate
and product concentration and the
presence or absence of co-factors and/or
inhibitors.
9
Enzyme - definition
Highly specific, organic, protein, catalysts that
work very rapidly in both directions and are
affected by heat, pH, radiation, substrate
and product concentration and the
presence or absence of co-factors and/or
inhibitors.
10
Enzyme - definition
Highly specific, organic, protein, catalysts that
work very rapidly in both directions and are
affected by heat, pH, radiation, substrate
and product concentration and the
presence or absence of co-factors and/or
inhibitors.
11
Enzyme - definition
Highly specific, organic, protein, catalysts that
work very rapidly in both directions and are
affected by heat, pH, radiation, substrate
and product concentration and the
presence or absence of co-factors and/or
inhibitors.
12
Enzyme - definition
Highly specific, organic, protein, catalysts that
work very rapidly in both directions and are
affected by heat, pH, radiation, substrate
and product concentration and the
presence or absence of co-factors and/or
inhibitors.
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Enzyme - definition
YOU’RE
BRILLIANT
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Role of enzymes in plants & animals
Control the rate of metabolic reactions
e.g. Amylase – converts starch to maltose
e.g. DNA polymerase – forms and repairs DNA
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Role of enzymes in metabolism
All metabolic activities are enzyme controlled
reactions
i.e. enzymes control the rate of respiration,
photosynthesis, etc.
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Enzymes involved in chemical
breakdown
• Amylase
• Pepsin
• Catalase
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Experiments
1. Investigate the effect of temperature on the
rate of one of the following: amylase, pepsin
or catalase activity.
2. Investigate the effect of pH on the rate of
one of the following: amylase, pepsin or
catalase activity.
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Immobilised enzymes
(1/5)
NB: Enzymes are catalysts and are reusable.
Amylase soln.+ Strarch soln.  Maltose soln. +
Amylase soln. mixed together.
Very difficult to separate the sugar soln. without
destroying the amylase.
Amylase enzyme cannot be reused
This is very wasteful
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Immobilised enzymes
(2/5)
• If the enzyme is placed in beads of gel from
which it cannot diffuse, then it can be
retrieved and reused easily.
• This is enzyme immobilisation.
• Tanks can be filled with the beads
(bioreactors) for large scale industrial
processes.
• This is bioprocessing
• Slower but more cost effective
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Immobilised enzymes
(3/5)
Methods of immobilisation:
1. physically attaching enzymes to insoluble
surfaces e.g. glass beads, charcoal, clay
2. entrap them in gels – which must be
permeable to the substrate and product –
but must prevent the enzyme leaving the gel
3. enclosed by a membrane
4. bonded to a support e.g. collagen
5. bonded to each other
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Immobilised enzymes
(4/5)
Advantages:
1. Easy recovery of enzymes for reuse
2. Easy harvesting of products (no enzyme
contamination)
3. Greater enzyme stability
4. Extends the life of proteolytic enzymes (digest
proteins) by preventing them digesting each other
5. Efficiency of the enzyme not affected
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Immobilised enzymes
(5/5)
Uses:
1. Use in bioreactors e.g. corn starch to corn syrup.
2. Fructose production
3. Clarification of fruit juices
4. Meat tenderisation
5. Vinegar production
6. Diagnostic reagents
See handout
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Active Site
The position on the enzyme where the
substrate is attached.
In an enzyme controlled reaction, the
enzyme and substrate combine to form the
enzyme-substrate complex.
The substrate molecules react, the products
are released and the unchanged enzyme is
available to catalyse another reaction.
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Specificity
An enzyme is like a mould that fits the
substrate exactly - only those substrates
that will ‘fit’ the enzyme will react with the
enzyme.
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Effect of pH on Enzyme Action
The shape of an enzyme relates to its
function.
If the shape is altered it makes the enzyme
less effective.
Hydrogen bonding in the enzyme helps
maintain the shape.
If the pH surrounding the enzymes changes
it affects the hydrogen bonds,
changes the shape and
makes them less effective.
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Optimum pH
Each enzyme has a specific pH at which it has the
shape that lets it work best.
This is its optimum pH.
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pH and rate of reaction graph
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Effect of Temp on Enzyme Action
In all chemical reactions an increase of 10°C
will generally double the rate of a reaction.
Temp will affect the rate of enzyme controlled
reactions also – up to a point.
If temp becomes too high – enzyme shape
changes.
If change is permanent – enzyme is
denatured
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Temp and rate of reaction graph
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END
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