Complete note covering all aspects required for Cambridge O Levels Biology, Unit 4 Enzymes. Includes detailed explanations, clear tables and diagrams to help you ace your exams.
Aspects covered in this note includes; catalyst, properties of enzymes, lock and key mechanism (how enzymes work), diges...
A catalyst is a substance that increases the rate of chemical reaction by providing an alternative path
with lesser activation energy for the chemical reaction to take place. Remember that catalysts do not
change in the reaction and can be used again.
An enzyme is a protein molecule that functions as a Biological Catalyst to speed up the rate of
metabolic reactions and remains unchanged at the end of the reaction.
Most enzymes made remain in the cell called as ‘Intracellular Enzymes’ but some enzymes might
be let out to work outside are called ‘Extracellular Enzymes’.
Properties of Enzymes
1. They are all protein molecules.
2. They are made in the cytoplasm under the instructions from the genes on the chromosomes in
the nucleus.
3. An enzyme works best at a particular temperature called the Optimum Temperature, and at a
particular pH called the optimum ph.
4. Enzymes are specific. (Only one kind of reaction is catalysed by a certain enzyme)
Lock and Key Mechanism/Hypothesis of Enzymes
Substrate = Key
Enzyme = Lock
Active site = Key
Hole
The enzyme has an active site with a specific shape so that only the specific substrate can bind
to the enzyme.
When a substrate binds the enzyme at the active site (like a key fitting the lock), the Enzyme
substrate complex is formed, causing an increase in the rate of reaction.
The products are formed and drift away, leaving the enzyme to operate again.
Either two substrates fit at the active site and a compound product is formed or one substrate
fits the enzyme and two separate products are formed.
The lock and key hypothesis can also be seen in the digestive system and is known as Hydrolysis.
Reactions that split larger molecules into smaller molecules is called Catabolic Reactions.
Reactions that join smaller molecules to form larger molecules is called Anabolic Reactions.
The names of Enzymes end with ‘ase’ and they are named according to the substance it acts upon.
To find the progress of enzyme catalysed reaction or the enzyme activity; we can always measure
the concentration of reactants, or the concentration of the products.
If decided to measure the concentration of reactants, it will be a descending graph as the
concentration of reactants gradually decrease as the reaction progresses with time.
If decided to measure the concentration of products, it will be an increasing graph as the
concentration of products gradually increase as the reaction progresses with time.
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