1. Enzymes
Chapter 5

2. Questions to answer! Lesson Objectives What are enzymes?
State the definition of enzymes.
How do enzymes work?
Explain the mode of action of enzymes in terms of active site, enzyme-substrate complex, lowering of activation energy, and enzyme specificity.
Describe the characteristics of enzymes.
3. What affects enzyme activity?
Investigate and explain the effects of temperature, pH, on the rate of enzyme-catalyzed reactions.
Where are enzymes used?
State 1 enzyme-catalyzed process.
Classify enzymes.

3. What are enzymes?
Definition of Enzymes
What are catalysts? How do they work?
Recall: What are proteins??
Enzymes are biological catalysts, commonly made of protein. They alter the rate of chemical reactions without themselves being chemically changed at the end of the reaction.
Properties of enzymes

4. condensation reaction
What are enzymes?
Recall: Proteins
Basic unit of proteins:
How amino acids are linked up:
Link between amino acids:
Long chains of basic units:
Polypeptides are folded and its 3D shape is held together by .
Weak bonds can be broken by heat and chemicals. The protein is said to be .
A denatured protein loses its .
amino acids
condensation reaction
peptide bond
polypeptide
weak bonds
denatured
function
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5. Enzymes are Biological Catalysts
How do enzymes work?
Enzymes are Biological Catalysts
A catalyst is a substance which can alter or speed up a chemical reaction.
Catalysts are not chemically-changed at the end of the reaction.

6. Enzymes are Biological Catalysts
How do enzymes work?
Enzymes are Biological Catalysts
Eg: Decomposition of Hydrogen Peroxide…
2H2O2 → 2H2O + O2
This reaction can be sped up by a catalyst,
manganese (IV) oxide.
Videos:
Dilute H2O2: H2O2 decomposition
Fresh H2O2: Last High School Chemistry Class
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7. Enzymes are Biological Catalysts
How do enzymes work?
Enzymes are Biological Catalysts
Eg: Decomposition of Hydrogen Peroxide…
2H2O2 → 2H2O + O2
This reaction can be sped up by a catalyst,
manganese (IV) oxide.
2H2O H2O + O2 + Heat
The same amount of manganese (IV) oxide remains after the reaction. It is not changed during the reaction.
Inorganic Catalyst
MnO2 (catalyst)

8. Enzymes are Biological Catalysts
How do enzymes work?
Enzymes are Biological Catalysts
The enzyme CATALASE can speed up hydrogen peroxide decomposition.
Enzymes are BIOLOGICAL CATALYSTS.
Video: Nosebleed Chemistry
2H2O H2O + O2 + Heat
Biological Catalyst
(Organic)
Note: Catalase is also found in potatoes!
Catalase (enzyme)
How do enzymes work?

9. How do enzymes work?
Activation Energy
The energy needed to start a chemical reaction is called activation energy.
Once the reaction has received enough energy, the rest of the reaction occurs spontaneously.

10. How do enzymes work?
Activation Energy
Enzymes lower the activation energy required to start a chemical reaction.
Reactants
Products
Enzymes do not change the energy level of reactants and products.
Enzymes only lower the ‘height’ of the ‘activation energy hill.’

11. Lock and Key Hypothesis
How do enzymes work?
Lock and Key Hypothesis
The substances on which enzymes act are called substrates.
Enzymes bind to substrates by the lock and key hypothesis. AB
enzyme molecule is free to take part in another reaction
a new substance (product) AB leaves the active sites
active sites A B
enzyme molecule (the ‘lock’)
substrate molecules (A and B) can fit into the active sites
enzyme-substrate complex

12. Lock and Key Hypothesis
How do enzymes work?
Lock and Key Hypothesis
Enzyme reaction depends on the presence of active sites.
Active sites have a specific 3D shape.
Specific substrate molecules fit into the active site like a lock and key.
Substrate binds to the enzyme, forming an enzyme substrate complex.
Reactions take place at the active sites to convert substrate molecule(s) into product molecule(s).
Product molecule(s) separate, leaving the enzyme molecule unchanged and free to combine again with more substrate molecules.

13. Lock and key hypothesis
How do enzymes work?
Induced Fit Model
Current hypothesis for enzyme action
When a substrate molecule fits into an enzyme molecule, the enzyme molecule alters its shape slightly so that it fits more tightly around the substrate molecule.
This makes the chemical reaction easier.
Lock and key hypothesis
Induced Fit Model
Source:

14. Enzyme Characteristics
How do enzymes work?
Enzyme Characteristics
Enzymes are required in minute amounts
Enzymes are very efficient molecules.
They remain unchanged at the end of the reaction, and thus can be reused over and over again.
A of enzyme can catalyze a of chemical reactions.
small amount
large amount

15. Enzyme Characteristics
How do enzymes work?
Enzyme Characteristics
Enzyme Specificity
Enzyme action is highly specific: each chemical reaction is catalyzed by a unique enzyme.
The enzyme’s specificity is due to its 3-dimensional surface configuration.
The shape of the substrate must be complementary to the shape of the enzyme’s active site.
The shape of an enzyme can be affected by high temperature and acids and alkalis.

16. Enzyme Characteristics
How do enzymes work?
Enzyme Characteristics
Enzymes catalyze reversible reactions
Some reactions in living cells are reversible. They can proceed in the forward or backward direction.
Some enzymes catalyze both forward and backward reactions until an equilibrium is reached. This occurs when the amount of reactants equals the amount of products formed.

17. Enzyme Characteristics
How do enzymes work?
Enzyme Characteristics
Some enzymes require coenzymes
Some enzymes require a coenzyme (another compound) to be bound to them before they can catalyze reactions.
Coenzymes are non-protein organic compounds.
Eg. of coenzymes: Vitamin B complex

18. What affects enzyme activity?
4 Factors
Enzymes are affected by the following:
Temperature pH
Enzyme concentration
Substrate concentration

19. What affects enzyme activity?
Temperature
Enzymes have an optimum temperature.
This is the temperature at which the enzyme catalyzes the largest number of reactions per second.
The optimum temperature of enzymes varies in different organisms, and is often but not always close to the temperature at which the enzyme usually functions.
Some enzymes may have very high or very low optimum temperatures.

20. What affects enzyme activity?
Temperature
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 10°C 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
K (optimum temperature) D
Temperature

21. What affects enzyme activity?
Temperature
As temperature rises…
Particles of matter are in constant random motion.
In the reaction, the enzyme and substrate molecules move and collide with one another at random.
Raising the temperature increases the kinetic energy of the molecules.
The substrate and enzyme molecules collide with each other more often, increasing the chance of substrates fitting into active sites.
The rate of formation of enzyme-substrate complex increases, increasing the rate of formation of products.

22. What affects enzyme activity?
Temperature
As temperature rises…
Enzyme activity increases as the temperature increases up to the optimum temperature.
At high temperatures, enzyme activity decreases.
Enzymes are made of , and its 3D shape are held together by .
At high temperatures, the vibrations of the atoms in the enzyme vibrate so violently that they break the weak bonds in the enzyme.
The enzyme loses its shape and becomes denatured.
The higher the temperature, the faster the rate of denaturation.
proteins
weak bonds

23. What affects enzyme activity?pH
Enzymes are affected by the acidity or alkalinity of the solutions they are in.
Acid or alkali can interact with the enzyme molecule, causing the protein to change its shape.
Extreme changes in pH of the solutions denature the enzymes.
Enzymes also have an optimum pH – the pH at which the enzyme can best function in.

24. What affects enzyme activity?pH

25. Enzyme & Substrate Concentration
What affects enzyme activity?
Enzyme & Substrate Concentration

26. Enzyme & Substrate Concentration
What affects enzyme activity?
Enzyme & Substrate Concentration
In a solution of fixed enzyme concentration, as substrate concentration increases, the rate of reaction increases to a maximum.
Beyond the maximum point, increasing the substrate concentration will not increase the rate of reaction.
This is because at any point of time, all the enzyme molecules are in use. The enzyme molecules are saturated.
The enzyme concentration becomes the limiting factor.
The reaction rate will increase if the enzyme concentration is increased.

27. Digestion Some food molecules are large and insoluble in water.
Where are enzymes used?
Digestion
Some food molecules are large and insoluble in water.
These food molecules cannot through the cell surface membrane.
Some examples of large food molecules are , and .
The large molecules must first be converted into simpler smaller substances which are soluble in water and diffusible.
This is known as digestion, and is achieved by digestive enzymes.
diffuse
proteins
starch
fats

28. CONDENSATION REACTION
Where are enzymes used?
Digestion
Enzymes are involved in two types of reactions in the body:
Synthesis of complex substances from simpler ones
Break down of complex substances to simpler ones
CONDENSATION REACTION
HYDROLYTIC REACTIONS
Examples of hydrolysis in the body:
Large molecules of food are converted to smaller molecules by digestive enzymes.
In cell respiration, glucose is broken down to carbon dioxide and water and release energy.
Hydrogen peroxide can be produced in chemical reactions in cells. It is toxic to tissues. Cells produce enzyme catalase which catalyses the breakdown of hydrogen peroxide.
Examples of condensation reactions in the body:
Forming from glucose
Forming proteins from
starch
amino acids
Enzymes catalyze practically ALL the chemical reactions that occur in an organism!

29. Classification of Enzymes
Where are enzymes used?
Classification of Enzymes
Enzymes are classified according to the chemical reactions they catalyze.
Enzymes that catalyze hydrolytic reactions are known as hydrolases.
Oxidation-reduction enzymes are involved in breaking down glucose during respiration.
Enzymes were previously named by the persons who discovered them.
Nowadays, enzymes are named according to a scientific system.

30. Classification of Enzymes
Where are enzymes used?
Classification of Enzymes
Type of hydrolase
Example(s)
Carbohydrases digest carbohydrates
Salivary amylase (in the mouth) and pancreatic amylase. Both digest starch.
Cellulases digest cellulose. It is produced by some bacteria. It is not found in mammals.
Proteases
digest proteins
Pepsin in the stomach
Lipases
digest lipids (fats)
Lipase in pancreatic juice

31. Where are enzymes used?
Industrial Uses
Enzymes are used in industry as they can bring about chemical changes at low temperature.
Chemical reactions at low temperatures are easier to control and cheaper to run.
Enzymes can be extracted from living cells and used in their pure form.

32. Where are enzymes used?
Industrial Uses
Microorganisms producing useful enzymes can be used in industry to make cheese, yoghurt and beer.
Catalase can be added to latex containing hydrogen peroxide to produce oxygen to form foam rubber.
Enzyme specificity makes them ideal for use in analysing chemicals.
Enzymes can be used to detect glucose in urine.
This can help to detect diabetes.
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34. Enzymes Definition of enzymes
Pure Biology Chapter 5
Definition of enzymes
Enzymes are biological catalysts, commonly made of protein. They alter the rate of chemical reactions without themselves being chemically changed at the end of the reaction.
Enzymes
have specific
are
Functions
Proteins as
Remain chemically unchanged at the end of the reaction
Biological catalysts
are
form
speed up
Enzyme-substrate
complex
Rate of
reaction
affected by
Inactivated
Denatured
Enzyme
concentration
Substrate
concentration pH
Temperature
with the help of by
at low
at high
by lowering
are of
at extreme
Coenzymes
Lock-and-key
hypothesis
Induced-fit
model
Activation
energy
Chemical reactions
involve
Intracellular
enzymes
Extracellular
enzymes
found in
Digestive
system
examples
is the
Specific binding
of enzyme
Lipases
Proteases
Carbohydrases to
digest
digest
digest
Substrate
Lipids
Proteins
Carbohydrates
to form
to form
to form
to form
Specific
product(s)
Fatty acids and glycerol
Amino acids
Simple sugars

35. Remain chemically unchanged at the end of the reaction
Pure Biology Chapter 5
Definition of enzymes
Enzymes
have specific
are
Functions as
Remain chemically unchanged at the end of the reaction
Biological catalysts
are
form
speed up
Enzyme-substrate
complex
Rate of
reaction
affected by
Inactivated
Denatured
Enzyme
concentration
Substrate
concentration
with the help of by
at low
at high
by lowering
are of
at extreme changes of
Coenzymes
Induced-fit
model
Chemical reactions
involve
Intracellular
enzymes
Extracellular
enzymes
found in
examples
is the
Specific binding
of enzyme
Lipases to
digest
digest
digest
Substrate
Proteins
Carbohydrates
to form
to form
to form
to form
Specific
product(s)
Simple sugars