2. What is a catalyst?
●A substance that speeds up the rate of a
chemical reaction.
●Enzymes are biological catalysts.
3. What is an enzyme?
●Enzymes are special compounds produced by
living cells in a body of an organism that allow
chemical reactions to take place at a faster
rate.
●They act as catalysts.
●They are made of protein.
●They alter the rate of chemical reactions
without themselves being chemically changed.
●Each enzyme has a unique shape.
4. Importance
●Vital to maintain normal functioning in an
organism
●Enzymes can either :
○break down complex substances into
simpler substances ( catabolism );
●OR
○build up complex substances from simpler
substances ( anabolism ).
6. Types of enzymes
1.Extracellular enzymes
●Enzymes leave the cell in which they
were produced to exert their functions
outside the cell.
●Eg. salivary amylase
2.Intracellular enzymes
○Enzymes exert their action inside the cells
○Egs. lysozyme in lysosomes
7. Classification of enzymes
1.Hydrolysis = splitting of water (water
molecules are needed to break down complex
molecules)
2.Called hydrolases
○carbohydrases (carbohydrates)
○amylases (starch)
○cellulases (cellulose)
○proteases (proteins)
○lipases (fats)
11. Active site
They are specific depressions or ‘pockets’ on the
surface of an enzyme molecule into which only a
complementary substrate can fit.
12. Lock and Key Hypothesis
The ‘lock’ = enzyme
The ‘key’ = substrate
This clearly explains how enzymes are highly specific due to
the complementary shape-pairing for its targeted substrates.
13. Induced-fit Hypothesis
●The active site is flexible and does not initially exist in the
shape complementary to the substrate.
●Enzyme enfolds substrate when it binds to the active site.
●Active site is moulded into a shape complementary to that
of the substrate, which enables it to perform its catalytic
function most effectively.
14. How do enzymes speed up
chemical reactions?
●Enzymes increase the rate of a reaction.
●Enzymes DO NOT increase the amount of product
formed at the end of the reaction.
Time
Amount of
reactant
left
Time
Amount of
product
formed
15. ●Enzymes lower the activation energy of a chemical
reaction
●They allow the reactions to be carried out at a
LOWER TEMPERATURE RANGE!
How do enzymes speed up
chemical reactions?
17. How do enzymes speed up
chemical reactions?
●In any chemical reaction, molecules must reach a
certain energy state before reaction is possible. This
is known as the activation energy.
●The activation energy acts as a barrier to the
reaction.
●The activation energy can be overcome through
increasing the temperature and pressure.
●Enzymes lower the activation energy needed to start
a chemical reaction.
18. How do enzymes speed up
chemical reactions?
●Activation energy is lowered because
enzymes form the enzyme-substrate
complex.
●This causes a redistribution of electrical
charge, which strains the chemical bonds
within the substrate.
●Therefore, more molecules can cross the
energy barrier and the reaction rate is faster.
19. Characteristics of Enzymes
1.Enzymes and speed of chemical
reactions
●Enzymes alter or speed up the rates of
chemical reactions that occur in a cell.
●Enzymes remain unchanged in the
reactions
●Enzymes can be reused over and over
again
20. 2. Enzymes are required in minute
amounts
●A very small amount of enzyme is
capable of catalyzing a huge reaction
Characteristics of Enzymes
21. 3. Enzymes are VERY specific.
●Amylases will only act on starch and NOT
on proteins or fats.
●The substances that enzymes act on are
called substrates ( starch, proteins and
fats)
Characteristics of Enzymes
22. 4. Enzyme activity is affected by temperature.
●The activity of the enzyme and the rate of reaction
is highest at the optimum temperature.
●At low temperatures, enzymes are inactive.
●As temperature rises, the rate of reaction
increases because:
○Heating leads to an increase in kinetic energy
of molecules.
○This leads to more successful collisions, and
more formation of enzyme-substrate
complexes.
●Beyond the optimum temperature, the enzyme
activity decreases as the enzyme is denatured.
Characteristics of Enzymes
24. Enzyme activity is affected by temperature
●Enzymes are protein in nature.
●Proteins are denatured at high
temperatures.
●Denaturation is irreversible
25. Enzyme activity is affected by temperature
●The 3D shape of the active site is determined by
weak hydrogen bonds that hold the chains of amino
acids in place.
●An increase in temperature causes vibrations in the
atoms of the enzyme, causing the hydrogen bonds
to be disrupted/break.
●The active site loses its shape and is no longer
complementary to the substrate.
●The enzyme can no longer act as a catalyst.
26. 5. Enzyme activity is affected by pH
●Enzymes are affected by the acidity or
alkalinity of solutions.
●Some work best in acidic environment
○eg pepsin)
●Alkaline environment
○intestinal enzymes eg amylase
●Extreme changes in pH can denature the
enzymes.
Characteristics of Enzymes
28. ●Enzymes are made of proteins.
●The 3D shape of the active site is determined by
weak hydrogen bonds that hold the chains of
amino acids in place.
●Interference of the H+ or OH- ions with the
hydrogen bonds causes them to be disrupted.
●The active site loses its specific shape and is no
longer complementary to the substrate.
●The enzyme is denatured.
Enzyme activity is affected by pH
29. Why do enzymes denature?
1.Enzymes are made of proteins
2.Proteins heat them up changes their
shape
3.Their 3-D structure is changed.
4.Changes are made to the active site.
31. What happens at low substrate
concentration?
●At low substrate concentrations, collisions
between enzyme and substrate molecules are
infrequent and reaction proceeds slowly.
●As the substrate concentration increases, the rate
of reaction initially increases proportionately as
collisions between enzyme molecules and
substrates become more frequent.
34. Why are enzymes required in
small amounts?
●Enzymes remain unchanged at the end of a
reaction.
●The active site of an enzyme may be used
again.
●Therefore, enzymes can work efficiently at low
concentrations.
●Provided that the substrate(s) are present in
excess, increasing the enzyme concentration
will increase the rate of reaction.
35. Why are enzymes
specific?
●This allows control over when and where reactions
happen.
●Enzymes are specific due to the three-dimensional
surface configuration of the active site.
●The active site of the enzyme has a specific shape
and distribution of charge that is complementary to
that of its substrate.
●This is explained by the lock and key hypothesis.
36. Summary
Characteristics of enzymes
1.Enzymes speed up chemical reactions.
2.Enzymes are required in small amounts.
3.Enzymes are specific.
4.Enzymes are affected by temperature.
5.Enzymes are affected by pH.
6.Enzymes catalyse reversible reactions.
37. Summary
Factors affecting the rate of an enzyme
reaction
●Enzyme concentration
●Substrate concentration
●Temperature
●pH
●Presence of inhibitors
38. Question
Which graph shows how temperature affects the
rate of an enzyme-controlled reaction?
Temperature
Rate
Temperature
Rate
Temperature
Rate
Temperature
Rate
A
B
C
D
39. The diagram shows an experiment to investigate the
action of a protease enzyme on a 1g cube of raw meat.
After 15min at 20˚C, 0.25g of the protein was converted
into amino acids. How much protein would be digested if
the experiment was repeated at a temperature of 30˚C?
1.0.0g
2.0.15g
3.0.25g
4.0.50g
Question
Protease solution
1.0g cube of
meat
42. Question
Three wells were cut in agar jelly, which is made of starch.
A different solution was placed in each well. Twelve hours
later, the jelly was flooded with iodine. The diagram below
shows the final appearance of the jelly. Which solutions
could have given the results shown?
2
1
3
Well 1 Well 2 Well 3
A Amylase +acid Amylase Boiled amylase
B Amylase +acid Boiled amylase Amylase
C Amylase Amylase +acid Boiled amylase
D Amylase Boiled amylase Amylase +acid
