2. Learning Objectives
At the end of the lessons, students should be able to:
• Define what is an enzyme
• Explain enzyme action in terms of the ‘lock and key’
hypothesis.
• Explain the mode of action of enzymes in terms of an
active site, enzyme-substrate complex, lowering of
activation energy and enzyme specificity. (PURE)
• Investigate and explain the effects of temperature, pH
on the rate of enzyme catalysed reactions.
4. What are Enzymes?
•Biological catalyst made of protein
•Speed up chemical reactions in living
organisms without themselves being
chemically changed at the end of the
reactions
5. Some important Terminologies
Substrates (Reactants)
• Substances on which enzymes act on
• Eg: Starch (substrate) which salivary
amylase acts on
Active Site
• Depressions on the surface of an
enzyme molecule where the
substrate can fit
7. How does Enzymes work?
Picture this…
Enzymes
Complex molecules Simpler molecules
8. How does Enzymes work?
Picture this…
Enzymes
Simple molecules Complex molecules
What is needed for the a
chemical reaction to take place?
9. •To start a chemical reaction, a certain
amount of energy is needed.
•This amount of energy is called
activation energy
How does Enzymes work?
Pg 7
10. • Enzymes work by lowering the activation
energy required to start the reaction.
• In this way, the reaction is sped up
How does Enzymes work?
Pg 7
12. What are the types of Enzyme
Reactions?
Break down complex
substances
Build up complex
substances
13. Types of Enzyme Reactions
Break down complex molecules into
simpler molecules
• E.g. digestion of maltose to glucose
maltase
14. Types of Enzyme Reactions
Build up complex molecules from simpler
molecules
• E.g. Glucose Glycogen
Glycogen
synthase
GlycogenGlucose molecules
15. Classification of Enzymes
Type of Enzyme
Carbohydrase
Protease
Lipase
Type of Substrate
Fats/ Lipids
Protein
Carbohydrates
Example of Enzyme
Maltase
Pepsin
Intestinal Lipase
16. Properties of Enzymes
1. Speeds up chemical reaction
2. Required in small amounts
3. Specific in action
4. Affected by temperature
5. Affected by pH
6. Catalyse reversible reactions
17. 1. Enzymes speed up chemical reaction
Properties of Enzymes
• By lowering the activation energy needed to start the
reaction
18. 2. Enzymes are required in minute amounts
Properties of Enzymes
• Enzymes remain chemically unchanged after a
chemical reaction
• Can be reused again & again
19. 3. Enzymes are specific in action
Properties of Enzymes
• One kind of enzyme will catalyse only one kind of
chemical reaction
• Substrate specific (Lock & Key hypothesis)
20. 4. Enzymes are affected by temperature
Properties of Enzymes
• Enzymes are made up of proteins
• Enzymes denatures at high temperatures
• Enzymes are inactive at low temperatures
22. Effect of Temperature on
Enzyme Reaction
A
• Enzymes are inactive at very low temperatures
• Low rate of reaction
Enzymes are
not destroyed
at very low
temperatures
23. Effect of Temperature on
Enzyme Reaction
B
• Enzyme activity increases as temperature rises
• Rate of reaction
increases
Molecules moves
faster in higher
temperatures,
substrate & enzyme
will collide more often
24. Effect of Temperature on
Enzyme Reaction
C
• Enzyme activity reaches its maximum rate
• At the optimum
temperature
Most enzymes
have an
optimum
temp of 40 oC
25. Effect of Temperature on
Enzyme Reaction
D
• Enzyme rate of reaction decreases ZERO
• The enzymes
denatures
The structure of the
active site changes
substrate cannot
bind rxn
decreases
28. 5. Enzymes are affected by pH
Properties of Enzymes
• Enzymes are made up of proteins
• Enzymes denatures at extreme pH
• Acidic / Alkaline
29. Effect of pH on
Enzyme Reaction
• Optimum pH:
• The pH value at which the rate of enzyme reaction
is the highest
• Extreme pH:
• Denatures enzymes
• Changes the structure of the active site
31. 6. Enzymes catalyse reversible reactions
Properties of Enzymes
• Reactions can proceed in forward and
backward direction
• Eg:
CO2 H2CO3H2O+
carbonic
anhydrase
WaterCarbon
dioxide
Carbonic
acid
32. The enzyme & substrate molecules will
combine to form a temporary structure called
enzyme-substrate complex
Some important Terminologies
33. Action of Enzyme
(Build Up Reaction)
enzyme
substrate
enzyme
product
enzyme-
substrate
complex
Pure
34. Action of Enzyme
(Break Down Reaction)
enzyme
product
enzyme
substrate
enzyme-
substrate
complex
Pure
35. Which statement is true of all enzymes?
Micro Ques 1
( D )
A They are denatured at temperatures above 60 oC.
B They are inhibited at low pH values.
C They catalyse the breakdown of large molecules
into smaller ones.
D They are required in small amounts.
36. 2 ml of amylase solution is added to 5ml of starch solution which is
kept in a water bath maintained at 70 oC. Then the mixture is cooled
down from 70 oC to 10oC. Which of the following shows the change
in the reaction rate of this mixture ?
Micro Ques 2
( D )
37. An enzyme may be inactivated by ___________.
Micro Ques 3
( B )
A removing the products of the reaction as they appear
B blocking its active site
C halving the concentration of the enzyme
D adding another metal as co-enzyme
38. MicroQuestion
• Qn1: Enzymes speed up rate of reaction, Highly
specific in their reaction. Remain chemically
unchanged at end of reaction, hence they are required
in small amount. The enzymes reaction can be
affected by temperature and pH.
• Qn2: It refers to the depression in the enzyme that
substrate can fit it.
• Qn3: Breakdown of complex molecules and build up
of complex molecules from simples molecules.
39. !! Activity Time !!
Each of you should
get either a KEY or a
LOCK
40. You have 5 mins to look for the key
that opens your lock!
41. Lets Reflect!
• What does the lock represent?
• Enzyme
• What does the key represent?
• Substrate
• Where is the active site?
• In the lock
42. Issues with the
Lock & Key Hypothesis
The lock (enzyme) changes
shape after the reaction
*Enzymes are unchanged
after the reaction
The key (substrate) does not give
rise to any new products
*Substrates give rise to new
products with the help of enzymes
43. Enzymes
In conclusion, enzyme action is specific due to
the shape of the substrate and active site
being complementary to each other.
An exothermic reaction is a chemical or physical reaction that releases heat. It gives out energy to its surroundings. The energy needed for the reaction to occur is less than the total energy released.
An exothermic reaction is a chemical or physical reaction that releases heat. It gives out energy to its surroundings. The energy needed for the reaction to occur is less than the total energy released.
