Title: Chapter 5 - Enzymes
1Chapter 5 - Enzymes
- What Are Enzymes?
- Classification of Enzymes
- Characteristics of Enzymes
2Learning Objectives
- Candidates should be able to
- Define enzymes as proteins which function as
biological catalysts.
3 What Are Enzymes?
- Enzymes are
- Biological catalysts,
- Protein in nature,
- Catalyze chemical reactions without being changed
at the end of the reaction.
4Enzymes as catalysts
- Enzymes lower the activation energy of a reaction
so that it occurs more readily.
5Activation Energy
Imagine a chemical reaction as the process of
rolling a huge stone (reactant) up a hill so that
it rolls down and breaks into tiny pieces
(products).
1
6Activation Energy
Imagine a chemical reaction as the process of
rolling a huge stone (reactant) up a hill so that
it rolls down and breaks into tiny pieces
(products).
1
Activation energy is the energy needed to roll
the stone up the hill.
2
7Activation Energy
Imagine a chemical reaction as the process of
rolling a huge stone (reactant) up a hill so that
it rolls down and breaks into tiny pieces
(products).
1
Once over the hill, the rest of the reaction
occurs.
3
Activation energy is the energy needed to roll
the stone up the hill.
2
8Activation Energy
Imagine a chemical reaction as the process of
rolling a huge stone (reactant) up a hill so that
it rolls down and breaks into tiny pieces
(products).
1
Once over the hill, the rest of the reaction
occurs.
3
Activation energy is the energy needed to roll
the stone up the hill.
2
The stone rolls down and breaks into tiny
pieces (products are formed).
4
9Activation Energy
Imagine a chemical reaction as the process of
rolling a huge stone (reactant) up a hill so that
it rolls down and breaks into tiny pieces
(products).
1
Once over the hill, the rest of the reaction
occurs.
3
Activation energy is the energy needed to roll
the stone up the hill.
2
The stone rolls down and breaks into tiny
pieces (products are formed).
4
The energy needed to start a chemical reaction
is called activation energy.
5
10Digestion An Enzyme Process
- Why do we need to digest our food?
- Starch, proteins and fats are very large.
- They cannot diffuse across cell membranes for
absorption. - Therefore, they must be digested into
- Simpler, smaller and soluble substances.
- Diffusible across cell membranes.
11Other applications of Enzymes
- Anabolic processes
- Eg. Synthesis of proteins from amino acids.
- Catabolic processes
- Eg. Oxidation of glucose (tissue respiration)
- Catalase production
- Catalase catalyses the breakdown of toxic
hydrogen peroxide into harmless water and oxygen. - Catalase is abundant in liver and blood.
12 Classification of Enzymes
- Enzymes are classified
- according to the chemical reaction involved in
- Enzymes that catalyse hydrolysis reactions are
called hydrolases. - Example of hydrolases
- Carbohydrases, proteases, lipases.
- Enzymes involved in oxidation of food as called
oxidation-reduction enzymes.
13Learning Objectives
- Candidates should be able to
- Explain enzyme action in terms of the lock and
key hypothesis. - Investigate and explain the effects of
temperature and of pH on the rate of enzyme
catalyzed reactions .
14Characteristics of Enzymes
- Enzymes alter or speed up the rates of chemical
reaction that occur in a cell. - Enzymes are required in minute amounts.
- Since enzymes are not altered in a chemical
reaction, a small amount can catalyse a huge
reaction.
15Enzymes are specific
- Specificity of enzyme is due to its shape (or
surface configuration). - The substrate will fit into an enzyme, forming an
enzyme-substrate complex. - The product will then be released.
16Lock and key hypothesis
- What is the lock and key hypothesis?
- It is the old view of enzyme specificity, that
there was an exact match between the active site
and the substrate.
17A synthesis/ dehydration Rx.
18Lock and Key Hypothesis
active sites
enzyme molecule (the lock)
B
A
substrate molecules ( A and B) can fit into the
active sites
19Lock and Key Hypothesis
active sites
enzyme molecule (the lock)
B
A
substrate molecules ( A and B) can fit into the
active sites
enzyme-substrate complex
20Lock and Key Hypothesis
active sites
enzyme molecule (the lock)
B
A
enzyme molecule is free to take part in another
reaction
substrate molecules ( A and B) can fit into the
active sites
enzyme-substrate complex
AB
a new substance (product) AB leaves the active
sites
21Induced fit hypothesis
- What is induced fit hypothesis?
- shape of the active site adjusts to fit the
substrate.
22Induced fit hypothesis
- How did induced fit hypothesis come about?
- - recent imaging technology demonstrated changes
in the 3-D conformation of enzymes when
interacting with their substrates.
23Effect of temperature
- At low temp
- Rate of reaction is slow.
- Enzymes are inactive at low temp.
- Every 10oc rise in temp, rate of reaction
increases by double - (till it reaches optimum temp).
24Effect of temperature
- At optimum temp
- Rate of reaction is the highest.
- Enzymes are most active.
- Beyond optimum temp
- Rate of enzyme activity decreases sharply.
- Enzymes are being denatured.
- Hydrogen bonds are easily disrupted by increasing
temperature.
25Effect of temperature
26Effect of Temperature on the Rate of Reaction
The optimum temperature is reached. Enzyme is
most active.
3
Rate of reaction (enzyme activity)
Beyond the optimum temperature, enzyme
activity decreases.
4
As the temperature rises, enzyme activity
increases as indicated by the increase in the
rate of reaction it catalyses. Usually the enzyme
is twice as active for every 10C rise in
temperature until the optimum temperature is
reached.
2
At point D, the enzyme has lost its ability to
catalyse the reaction.
5
An enzyme is less active at very low
temperatures.
1
0
Temperature
K (optimum temperature)
D
27Effect of pH
- Enzymes have an optimum pH.
- Deviation from the optimum pH will decrease
enzyme activity.
28Effect of pH on Enzyme Activity
29Effects of substrate and enzyme concentration on
rate of reaction
- Increasing substrate concentration will increase
rate of reaction until a certain limit. - Cause
- Enzyme molecules are saturated.
- Enzyme concentration is now the limiting factor.
30What is a limiting factor?
- Any factor that directly affects the rate of a
process if its quantity is changed - The value of the limiting factor has to be
increased in order to increase the rate of the
process.
31Coenzymes
- What are coenzymes?
- Some enzymes require a coenzyme to be bound to
them before they can catalyse reactions. - Usually, coenzymes are non-protein organic
compounds. - Eg. Vitamins, especially the B complex vitamins.
32Coenzymes
- Coenzymes are altered in some way by
participating in enzyme reaction.
33Enzymes
- catalyse reversible reactions
products
reactants
C
D
B
A
reactants
reactants
34Enzymes
Characteristics
Functions
Mode of Action
affected by
Limiting factors
35Enzymes
36Enzymes
Biological catalysts, which are mainly made of
proteins. They speed up the rate of chemical
reactions without themselves being chemically
changed at the end of the reactions.
37Enzymes
Functions
38Enzymes
Functions
- Building up or synthesising complex substances
- Breaking down food substances in cells to
release energy (cellular respiration) - Breaking down poisonous substances in cells
39Enzymes
Characteristics
Functions
40Enzymes
Characteristics
Functions
- Speed up chemical reactions
- Required in small amounts
- Highly specific
- Work best at an optimum temperature and pH
- May need coenzymes for activity
- Some catalayse reversible reactions
41Enzymes
Characteristics
Functions
Mode of Action
42Enzymes
Characteristics
Functions
Mode of Action
- Lower the activation energy of a reaction
- Interact with the substrate according to lock
and key hypothesis to form an enzyme-substrate
complex
43Enzymes
Characteristics
Functions
Mode of Action
affected by
44Enzymes
Characteristics
Functions
Mode of Action
affected by
Limiting factors
Factors that directly affect the rate at which a
chemical reaction occurs if their quantity is
changed. The value of a limiting factor must be
increased in order to increase the rate of
reaction.
45Enzymes
Characteristics
Functions
Mode of Action
affected by
Limiting factors
e.g.
Temperature / pH
46Enzymes
Characteristics
Functions
Mode of Action
affected by
Limiting factors
- Increase in temperature increases the rate of
enzyme reaction until optimum temperature is
reached - Increase in pH increases the rate of enzyme
reaction until optimum pH is reached
e.g.
Temperature / pH
47Enzymes
Characteristics
Functions
Mode of Action
Classes
affected by
Limiting factors
e.g.
Temperature / pH
48Enzymes
Characteristics
Functions
Mode of Action
Classes
based on the type of reaction catalysed e.g.
affected by
Hydrolases
Limiting factors
e.g.
Temperature / pH
49Enzymes
Characteristics
Functions
Mode of Action
Classes
based on the type of reaction catalysed e.g.
affected by
Hydrolases
Limiting factors
Oxidation-reduction enzymes
e.g.
Temperature / pH