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Powerpoint@lecture Slides Are Prepared By Biology Lecturer, KMPk
14.1 : Properties of enzyme and mechanism of actions
14.2 : Cofactor
Enzymes?
Properties of Enzymes.
Activation Energy?
Mechanism of Enzyme Action :
Lock and Key Model
Induced-Fit Model
At the end of this subtopic, students should able to :
a) Explain Factors That Affect The Enzymatic
Reaction.
b) Explain The Types and Functions of Cofactors.
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FACTORS THAT AFFECT THE
ENZYMATIC REACTION
The rate of an enzyme-catalyzed reaction is affected
by :
Chemical and Physical Factor that alters the enzymes 3-D
shape :
Temperature
pH
Regulatory molecules
Concentration ofsubstrate and enzyme.
Chemicals that specifically influence the enzyme.
Cofactors
FACTORS THAT AFFECT THEENZYMATIC REACTION
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Effect of Temperature
Each enzyme has an optimal
temperature.
Optimal temperature: at which
an enzyme produces the highest
production rate.
Optimal conditions favor the
most active shape for the
enzyme.
Effect of Temperature
Effects the movement of enzyme.
Increase temperature : The rate ofan enzymatic reactions increase .
Substrates collide with active sites
more frequently.
Fastest conversion of the reactants
to product molecules.
Above optimal temperature:
Enzymes denatured
Rate of reactions drop sharply
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EFFECTS OF pH
Affects the charge of amino
acids side chains with carboxyl
or amino groups (active site).
Maximum rate of reaction
occurs at optimum pH (most
enzyme pH 6-8)
Different enzymes, different
optimum pH.
Example :
Pepsin and Trypsin
How does pH affect enzyme activity?
Ionic interactions (+ve andVe) hold enzymes together.
Deviation from optimal pH range : excess H+ / OH- .
Alters the acidic/ basic/ functional group/side chain of
amino acid in enzyme.
Shifts the balance between positively and negatively
charged amino acid residues.
Change in the bonds and tertiary structure breakdown.
Effect of Substrate Concentration
Reactionvelocity
Substrate concentration
Vmax
The amount of substrate will
affect the rate of reaction.
Substrate concentration
increases, rate of reaction will
increase proportionally.
Then it will level off.
All the enzyme molecules
(active sites) are occupied.
Once all enzymes are
occupied, increasing
substrate will no longer
have an effect on rate
Constant enzyme concentration
Graph showing effect of increasing substrateconcentration
Effect of Enzyme Concentration
Reactionvelocity
Enzyme concentration
2007 Paul Billiet ODWS
At low enzyme concentration
and the rate of reaction is low.
Great competition for the
active sites.
As the enzyme concentration
increases, the reaction can
proceed at a faster rate.
more active sites.
Substrate as a limiting factor. Constant substrate concentration
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COFACTORS
One or more nonprotein components
required by enzymes in order to function
efficeintly.
Atom or molecules that are not part of
the enzymes primary structure.
3 types :
Metal Ions/Activator (Inorganic)
e.g Zn2+ and Mg2+
Coenzymes (Small organic)
e.g vitamin (also as precursor )
Prosthetic groupwww.themegallery.com
Non-protein inorganic substances.
Assist in forming ES complex by bind temporarily either
enzyme or substrate molecule into more suitable shape.
Eg: Ca2+, Zn2+,Mg2+,Cl-
E.g : Salivary amylase - chloride (Cl-)
thrombokinase - calcium (Ca2+)
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Non-protein organic or organometallicsubstances.
Tightly or weakly bound to the enzyme.
Most vitamins act as coenzymes or raw material from which
coenzymes are made.
To remove functional group from one substrate and add it to
another substrate. E.g: Vitamin B6 and B12
nicotinamide adenine dinucleotide (NAD)
NAD act to dehydrogenases by acting as hydrogen acceptor.
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A metal or Coenzymes that are covalently or
noncovalently bound very tightly to their enzyme.
E.g:
prosthetic group of electron carrier cytochrome
and enzyme catalase.
FAD (riboflavin) - prosthetic group of the electron
carrier cytochrome. It take part in oxidation-
reduction reactions.
(Boyer. Concepts in Biochemistry. Wiley)
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Assist in forming the enzyme-substrate complex
by altering the active site into a more suitable
shape.
May function to withdraw electrons from the
substrate.
May involve in transfer of electrons / atoms /
chemical groups in enzyme reactions.
What is cofactor?
State THREE types of cofactor.
Describe the effect of pH, temperature , enzyme
and substrate concentration .
How do cofactors work in assisting an enzymatic
reaction?
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14.3 Inhibition