CHAPTER 5 METABOLISM AND ENZYMES

CHAPTER 5
METABOLISM AND

ENZYMES

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5.1 METABOLISM

D : All chemical reactions that occur in a living organism
 Involve the conversion of food into energy in the form of ATP

and the formation of carbohydrate, protein, lipid and nucleic
acid

Types of Metabolism in a Cell

Catabolism Anabolism

 Is the process of breaking down complex  Is the process of synthesizing complex
substances into simple substances molecules from simple molecules
 Releases energy  Absorb energy

 Ex: the breakdown of glucose during  Ex : the formation of glucose during
cellular respiration to generate energy photosynthesis

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5.2 ENZYME

D : is an organic catalyst that mostly made up of proteins and its produced by living
cell organism

C : not all enzymes are synthesized from proteins
 Substrate is a substances needed for an enzyme reaction
 Substrates will bind with enzymes at a specific site known as the active site and

form an enzyme-substrate complex

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Enzyme Nomenclature

 1960s, The International Union of Biochemistry and Molecular Biology (IUBMB)
introduced the enzyme nomenclature based on the substrate or reaction it
catalyses

 Name of enzyme : adding ‘ase’ to the name of the substrate it catalyses
 Ex : lactose (substrate ) lactase (enzyme)

lactose + water lactase Glucose + galactose

 However, there are also a few enzymes that do not follow this naming system,
especially enzymes that were discovered before the systematic naming system
was introduced

 Ex : Trypsin, pepsin and renin

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General Characteristics of Enzymes

Enzymes act rapidly Enzymes are only required in The structure of enzymes
Enzymes are biological small quantities and are remain uncharged and are not
catalysts that speed up reusable
biochemical reactions destroyed after a reaction
GENERAL The reaction of enzymes are
Some enzymes need CHARACTERISTIC specific. Only substrate that
cofactors to work more fit the form completely with
efficiently. An example of OF ENZYMES an enzyme in an active site
cofactor is vitamin B and
Enzyme activity can be can combine
magnesium ion slowed down or stopped by Most of the reactions
catalyzed by enzymes are
enzyme inhibitors. An
example of an inhibitor is reversible
heavy metal such as lead or
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mercury

INTRACELLULAR AND EXTRACELLULAR ENZYMES

INTRACELLULAR ENZYMES
 Synthesis in a cell for its own use

Ex : hexokinase enzyme that is used in the glycolysis process during cellular
respiration
EXTRACELLULAR ENZYMES

 Enzymes that are secreted outside the cell
 Ex : trypsin enzyme is produce by pancreatic cells and secreted into the

duodenum to break down polypeptides

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EXTRACELLULAR ENZYMES PRODUCTION

1. Ribosome is the 6 6. Secretory vesicles will
site of protein 2 move towards the plasma
synthesis membrane and fuse with it
1 to secrete extracellular
2. Protein synthesized by
ribosome enter the lumen 5 enzymes
of the rough endoplasmic
3 5. In the golgi apparatus,
reticulum and are the proteins are modified
transported through it 4 into enzymes and secreted
in secretory vesicles that
3. Once it reaches the end 4. The transport vesicle that are formed from the tip of
of the rough endoplasmic contains proteins moves towards
reticulum, the membrane the golgi apparatus and then fuses the golgi apparatus
buds off to form transport
with it PREPARED BY CIKGU HUSRITA MRSM TRANSKRIAN
vesicles

MECHANISM OF ENZYME ACTION

The specific Substrate A reaction takes THE ‘LOCK AND KEY’ HYPOTHEIS
substrate combines with the place and a
approaches the active site to form product is • Most enzymes are complex proteins made
enzyme enzyme-substrate created. The up of polypeptide chains that are folded into
product then three-dimensional structures
complex
leaves the active • Enzyme has an active site with a specific
site after the configuration that complements a specific
reaction is substrate molecule
complete
• The binding of a molecule substrate on an
active site of enzymes is specific like a
‘lock and key’ combination

• Enzyme = ‘lock’
• Substrate = ‘key’

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MECHANISM OF ENZYME ACTION

Activation energy is the energy Energy in system
needed to break the bond in the
substrate molecule before Enzyme Reaction
reaction can occur
The presence of enzymes will reduce the activation energy of a
Enzymes function by lowering the reaction
activation energy.

So the rate of biochemical
reactions in the cell is accelerated

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THE MECHANISM OF ENZYME ACTION AND FACTOR CHANGES

EFFECTS OF TEMPERATURE 3
 At optimal temperature, the
1–2
 At low temperature, the rate of enzyme reaction is at its
maximum. The optimal
reaction catalyzed by enzymes is low temperature for enzyme reactions
 Temperature rises, the kinetic energy in the human body is around 37ºC
4-5
of the substrate molecules and  After reaching the optimal temperature, any further increase in temperature will
enzymes also increases. reduce the enzyme activity rapidly until it stops at 60ºC
 This increases the frequency of  At this temperature, the enzymes become denatured as a chemical bonds in the enzyme
effective collision between the molecules break at extreme temperatures
substrate molecules and enzyme  The enzymes are unable to retain the three-dimensional form
molecules  The active site of enzymes changes
 The rate of reaction between enzymes  The substrate does not complement the active site of enzymes
and substrate molecules increases
 With every rise in temperature of
10ºC, the rate of reaction controlled by
the enzymes will double until it reaches
the optimal temperature

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THE MECHANISM OF ENZYME ACTION AND FACTOR CHANGES

 The enzyme activity is influenced by the pH of the
surrounding solution

 Generally all enzymes react most effectively at their optimal
pH

 Most enzymes are active in the range of between pH 6 and
8. for example, the salivary amylase works at pH 6.8

 However, there are some exceptions. For example, the pepsin
enzymes in the stomach act at the optimal pH range of
between 1.5 and 2.5

 The trypsin enzymes in the duodenum, on the other hand, only
works well in an alkaline medium, at a pH of around 8.5

EFFECTS OF pH

 The change in pH value changes the charge (ion H+) of the active site of enzymes PREPARED BY CIKGU HUSRITA MRSM TRANSKRIAN
and the substrate surface. As a result the enzyme-substrate complex cannot be
formed

 When the pH of the environment returns to the optimum level, the charge on the
active site will be restored. The enzyme will return to function as normal

 The extreme change in the pH value will break the structural chemistry bond and
change the active site of enzymes. Denatured enzyme

THE MECHANISM OF ENZYME ACTION AND FACTOR CHANGES

EFFECTS OF SUBSTRATE  If the concentration of enzymes is fixed while the concentration of substrate is
CONCENTRATION increased, the reaction rate controlled by enzyme will also increase, leading to
an increases in products created

1.
 when substrate concentration increases, the opportunity for an

effective collision between the substrate and enzyme molecules
also increase
 The reaction rate continues to increase until it reaches the
maximum level. The rate of reaction is constant

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 At the maximum level, the concentration of enzymes becomes a

limiting factor. The reaction rate can only increase when the
concentration in enzymes increases
 After reaching the maximum level, all active sites of enzymes are
saturated with substrate and are involved in the catalytic reaction

THE MECHANISM OF ENZYME ACTION AND FACTOR CHANGES
 When the concentration of enzyme increases,
EFFECTS OF ENZYMES the rate of enzyme reaction will increase
CONCENTRATION because of the presence of more active sites
that are ready for catalytic action

 If the concentration of an enzyme in one
reaction is doubled, the amount of substrate
converted to products per unit of time is also
doubled with the condition that there is an
excess supply of substrate

 At the maximum rate, the concentration of
the substrate becomes the limiting factor.
The rate of reaction can only be increased by
adding more substrate

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5.3 APPLICATION OF ENZYMES IN DAILY LIFE

• The enzymes used are Digestive
extracted from natural enzymes are
resources such as bacteria or used in the
are produces synthetically medical sector

• Immobilized Enzymes are Protease enzyme Amylase, lipase,
enzymes that combine with separates the protease and
inert and insoluble substances fish skin
to increase the resistance of cellulase enzymes
enzymes towards change in Lactase in bio detergent
factors such as pH and enzymes are
temperature used in lactose-

 With this method, the enzyme free milk
molecules will remain in the
same position throughout the Pectinase and Trypsin enzyme extracts fur
catalytic reaction and then be cellulase from animal hide to make
separated easily from its enzymes are
product used in juice leather products
production
 This technology is known as
immobilized technology

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