Cell metabolism and Enzymes
Metabolism
(all of the chemical reactions in a living thing)
Anabolic reactions
Small molecules are combined
to make larger molecules.
Energy is needed
Catabolic reactions
Large molecules are broken
down into smaller molecules.
Energy is given out.
Sources of energy in cells for
anabolic reactions
1. Solar energy
Sunlight is a source of energy capable of
being absorbed by cellular pigments e.g.
chlorophyll.
2. Cellular energy
Catabolic reactions in cells release energy
Enzymes
Enzymes – the key to it all
Almost all chemical reactions that take place inside
living things are controlled by enzymes.
Enzymes are biological catalysts – they change the
rate of reactions without getting used up themselves.
Every enzyme is a protein and has a specific 3D
shape.
Enzyme Action
• The substance that an enzyme acts on is
its substrate
• The substance(s) that the enzyme forms is
called the product(s)
Catabolic enzyme
• Catalyse is an enzyme that converts
hydrogen peroxide into water and oxygen
•Catabolic = breaks a big
molecule into smaller ones
Anabolic Enzyme
• DNA Polymerase is an enzyme that builds
DNA nucleotides from tiny nucleotide units
in our cells
Anabolic = makes small
molecules into bigger ones
Consider This
• Amylase is an enzyme found in saliva. It breaks
starch molecules into smaller maltose molecules
• What is the substrate?
• What is the product?
• Will amylase break fats into fatty acids +
glycerol? Why?
• Is this an example of a catabolic or an anabolic
reaction? Why?
And This
• DNA Polymerase is an enzyme that builds
DNA using tiny molecules in our cells
• What is the substrate?
• What is the product?
• Do you think DNA polymerase could do
the reverse reaction? Why?
Learning Check
• What is meant by a substrate?
• What is the unit formed when an enzyme
combines with its substrate called?
• Give an example of an anabolic reaction
• Give an example of a catabolic reaction
Enzymes and Temperature
Mandatory experiment
Investigation 1
• How does temperature effect the rate of
reaction of an enzyme?
Step A
1. 5g of chopped up
celery
2. 1 drop of washing
up liquid
3. 10mls of Buffer
solution
ALL INTO A
GRADUATED
CYLINDER
1. 5ml of Hydorgen peroxide
Step B
2. The graduated cylinder and contents
ALL IN A WATER BATH UNTILL THEY ARE THE
SAME TEMPERATURE AS THE WATER BATH
Step C
Add the hydrogen peroxide to the
graduated cylinder.
Time for 1 minute and see the volume
of oxygen made
Temperature and enzymes
• At very low temperatures molecules are
moving slowly and enzymes work slower
because of less collisions with substrate
• As temperature increases molecules start
to move and bump into each other causing
the rate of reaction to increase
Temperature and enzymes
• When the shape is fully lost the enzyme is
said to be denatured this is usually a
permanent condition
• Human enzymes work best at body
temperature (37°C)
• Plant Enzymes work best at 20-30 °C
Rate of reaction
• Above certain temperatures enzymes start
to lose their shape the rate of reaction
falls.
37
Temp (oC)
Check your learning
• Why does temperature have an effect on the
rate of reaction?
• Why do enzymes not work well at low
temperatures?
• As temperature increases what happens to
enzyme activity?
• What is the optimum temp for enzymes in plants
and humans?
• What happens when an enzyme loses its
shape?
Enzymes and pH
Mandatory experiment
• Investigation 2 - To investigate the effect
of pH on the rate of enzyme action
pH
•
•
•
•
pH scale goes from 0 -14
Less than 7 is acidic
7 is neutral
More than 7 is basic (or alkaline)
To investigate the effect of
pH on catalase activity
Step 1
Finely chop the celery.
Weigh 5 g of the chopped
celery.
Step 2
Add 10 ml of your pH buffer 4, one
drop of washing-up liquid and 5 g
of celery into a graduated cylinder.
Step 3
Add 5 ml of hydrogen peroxide to
a boiling tube.
Step 4
Place the graduated cylinder and the
boiling tube in a water bath at 25 °C –
until they reach the required temperature
Step 5
Add the hydrogen peroxide into
the graduated cylinder and
record the volume immediately.
Step 6
Time for 2 minutes and record
the final volume.
Enzymes and pH
• The best ph (optimum pH) is
usually pH 7
Rate of reaction
• pH is important for enzymes as it
can make enzymes change their
shape!
0
• Outside this they lose their shape
and get denatured
pH 14
Check your learning..
• What is an enzyme? Why are they needed
for our metabolism?
• What does rate of reaction of an enzyme
mean?
• What does an enzyme act on?
• What effect does temperature have on the
rate of activity of an enzyme?
• What effect does pH have on the rate of
activity of an enzyme?
Higher level –
The active site theory of enzymes
How enzymes work
• Enzymes are not flat they have a 3D
structure
• The active site is the specific part of the
enzyme which combines with the
substrate.
Enzymes – active site theory
Because of the special shape of the active site
enzymes are very specific about the reactions they
catalyse.
If the shape of the active site changes then the enzyme
cannot work and is denatured.
enzyme
products
reactant
active
site
1. Substrate fits
into the active site
2. Enzyme- substrate
complex is formed.
3. Products leave the
active site
The enzyme changes the
structure of the substrate
The enzyme changes
back to original shape
What conditions could denature an
enzyme?
Mandatory experiment
• Investigation 4: the effect of heat
denaturation of the activity of an enzyme
Put 5g of chopped celery into
two boiling tubes in water baths
at 100OC and 20OC for 10
minutes. Remove and cool.
Make up 2 graduated
cylinders with..
10cm3 of pH buffer 9
1 drop of washing up liquid
Add boiled celery to A
Add unboiled celery to B
Step 3
In a water bath at 20oC add 5 cm3 of hydrogen peroxide to
both graduated cylinders
Measure the volume of oxygen gas produced in two minutes
Check your learning…
• What is meant by the specificity of an
enzyme?
• How can the Active Site Theory explain
the specificity of enzymes?
• How can an enzyme be denatured?
• Give two features of a denatured
enzyme?
Immobilising enzymes
Bioprocessing
• Bio-processing is the use of enzyme
controlled reactions to produce a product
• Traditionally microorganisms such as
bacteria and yeast were
used but since the 1950’s
enzymes are being used
Immobilising enzymes
• Enzymes are often immobilised or fixed
(attached to each other or an inert substance) so
that they can be used repeatedly in a bioreactor
How to immobilise enzymes
• The enzyme can be trapped in beads
using sodium alginate and calcium
chloride
Mandatory experiment
• Investigation 4: To prepare an immobilised
enzyme and examine its application
Step 1
Making up the solutions
In one beaker – make up a sodium
alginate solution
In a second beaker – make up the
yeast solution
In a third beaker – make up
calcium chloride solution
Step 2
Trapping yeast enzyme sucrase in beads
Mix the yeast with the alginate
solution
Pull the yeast/alginate solution up
into the syringe
Drop the solution from the syringe
into the calcium chloride solution
Step 3
• Investigating the activity of the immobilised
enzyme compared to the normal enzyme
Filter the hardened beads through a sieve and rinse with
water.
Fill up seperating funnels with free
yeast and immobilised yeast
Dissolve 1 g of sucrose in 100 ml of distilled water. Pour
50 ml into each separating funnel.
Immediately test the products in
the beakers with glucose strips.
Repeat test every 2 minutes until glucose appears in
both beakers.
Run off the remaining product from each funnel into the
beakers and compare the turbidity* of the solution from both
funnels.
Advantages of Immobilised Enzymes
1. A gentle procedure is used so the efficiency
of enzyme is not affected
2. Immobilised enzymes can be easily recovered
from the product so you can get a pure sample
of product easily
3. Immobilised enzymes can be reused this cuts
costs
Uses of Immobilised Enzymes
• Immobilised sucrase converts sucrose into
glucose to fructose which is used to make
sweet foods like marshmallow
Learning check
• What is an immobilised enzyme?
• How are enzymes immobilised?
• What are the advantages of immobilising
enzymes?
• Can you give an example of what
immobilised enzymes are used for?