Biological Catalysts: IGCSE Biology (Cambridge)

Biological catalysts
IGCSE Biology (Cambridge)

 Keywords:
catalyst catalyse protein
Lipase amylase protease
substrate active site product
temperature optimum denature

 Enzymes are proteins, produced by
organisms ( living), that catalyse chemical
reactions.
 Also known as biological catalysts.
 vt. Speeds up
 Example:
 Enzymes can catalyse chemical reactions.
 noun.
 is a substance that speeds up a chemical
reaction and is no changed by the reaction.
Eg:
 Chemical Catalyst is used in the Chemistry,
 Biological Catalyst is used in the Biology
 The substances that enzymes work on called
substrates.
 The surface where the reaction takes place
on called active site
Is a substance transformed from
substrates, which are then released from
active site.
large small
 All enzymes have five important properties.
1. They are all proteins and have different

shapes.
Different shapes
 2. Each enzyme catalyses one reaction or
specific
 3. They can be used again and again
( many times)
 4. They are influenced by temperature
 5. They are influenced by pH
Example
:
Rate
Of
Reaction
0 10 20 30 40 50 60 70
Temperature/oC
The substrate ( the ‘key’) must have a shape that fits
exactly into the active site ( the ‘key hole’) of the enzyme
( the ‘lock’).
Amylase Catalysts Chemical Reactions
Fats Lipase Living Things
pH Proteins Lock & Key model
Specific Starch Temperature
Activation energy
 Breaking large small
 Building up small large
 Converting small small

protease
enzymes
Break down
protein
molecules
Carbohydrase
enzymes
Break down
carbohydrate
molecules
lipase
enzymes
Break down
fat
molecules
protease
proteins Amino acids
Break down to
carbohydrase Glucose
carbohydrate
Break down to
lipase
3 Fatty acids
fat and 1 glycerol
Break down to
Most Enzymes name with – “áse”
e.g. Lipase
protease
Amylase
Catalase
Rate of reaction of an enzyme changes at
different temperatures
Optimum temperature
Molecules gain Enzyme

Rate kinetic energy is denaturing
Of
Reaction
0 10 20 30 40 50 60 70
Temperature/oC
When temperature increases, the reaction also
increases as the molecules have more kinetic energy
But this only occurs up to the optimum

temperature (usually about 40oC)
The temperature at which the rate of reaction is

fastest is known as the optimum temperature
denatured
 The enzyme changes shape and the active site no longer matches
the shape of the substrate molecule
Rate of reaction
As temperature increasing:
Greater Kinetic Energy - Colliding quickly
At high temperatures:
Bonds break down.
Active site shape change.
Substrate no longer fits
Enzymes has been Denatured
 Enzymes from plants usually have
lower optimum temperature than
those from mammals. E.g..: 270C
Why?
 Plants cells are at low temperature
outdoor .
 Plants enzymes work best where they
live.
 Step 1: Two tubes and label A & B
A B
 Step 2: Put 5ml of starch solution into tubes
A B
 Step 3: Put tube A into refrigerator for 10mins
put tube B into Water Bath for 10mins
One student Another student

A B
Cold condition Hot condition

 Step 4: Use measuring cylinder to collect 5ml
saliva from mouth.
Measuring cylinder
 Step 5: Add 2ml saliva into each tube
A B
 Step 6: Use stop watch, every 2 mins, to use
pipette get some mix solution on the spotting
tile.
pipette
Spotting tile
 Step 7: Add one drop of iodine solution on the
mix solution of spotting tile.
Spotting tile
 Step 8: observe how many times step 7 we should
do to see blue-black color disappear.
13 9 5 No. 15 disappear.
4
14 10 6 So there are 14 still

3
have blue-black color.
15 11
7 2
12 So for this solution needs
8 14✖2min=28mins
1
Spotting tile
The activity and shape of enzymes is also
affected by pH
 Enzymes prefer to work at an optimum pH. Outside of its pH range
the enzyme is denatured.
Optimum pH
pepsin amylase
Rate
Of
Reaction
1 2 3 4 5 6 7 8 9 10 11 12
pH
NOT SYMMETRICAL MORE SYMMETRICAL
 Enzymes are not denatured by low
temperatures - They are just slowed down
 And will work again when the temperature is

suitable.
 Once an enzyme is denatured, the damage is

permanent.
 There is an enzyme is found in living cells and
it can speed up the breakdown of hydrogen
peroxide to produce oxygen gas.

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Biological catalysts

IGCSE Biology (Cambridge)

catalyst catalyse protein

Lipase amylase protease

substrate active site product

temperature optimum denature

1. They are all proteins and have different

 Building up small large

 Converting small small

Molecules gain Enzyme

But this only occurs up to the optimum

The temperature at which the rate of reaction is

One student Another student

Cold condition Hot condition

14 10 6 So there are 14 still

 And will work again when the temperature is

 Once an enzyme is denatured, the damage is

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