chapter 14 biocatalysis hour1
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7/30/2019 Chapter 14 Biocatalysis Hour1
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Powerpoint@lecture Slides Are Prepared By Biology Lecturer, KMPk
14.1: Properties of enzymes
and mechanisms ofactions
14.2: Cofactors
14.3: Inhibition
14.4: Enzyme Classificationaccording to common
name and IUB
14.1 : Properties of enzyme and mechanism of actions
At the end of this subtopic, students should able to :
a) Describe the properties of enzymes.
b) Explain the mechanism of enzyme action.
c) Describe the hypotheses related to its mechanism
of action :
Induced Fit Model
Lock and Key Model
What are ENZYMES?
An organic catalyst (usually a
protein)
that speeding up/accelerates a
specificchemical reaction
bylowering activation energy (EA)
required for that reactionswithout itself being affected by the
reaction.
Required Only in Small Amount.
They are not altered irreversibly during the course
of reaction.
Each enzyme can participate repeatedly in
individual reactions (reused).
Do not damaged or destroyed by reactions it
catalyses.
Gerald Karp. Cell and Molecular Biology: Concepts and Experiments 6 th edition. page 93
Specificity.
Highly specific (specific substrate)
Has a specific shape so only substrates of a
particular shape will fit the active site on an
enzyme
Catalyzing only one type of chemical reactions.
(Richard. A. Biochemistry. Page 54-55)
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They have no effect on the thermodynamics of
the reaction.
Do not supply energy for a chemical reactions
Only accelerates the rates at which a favorable
chemical reaction proceeds
Gerald Karp. Cell and Molecular Biology: Concepts and Experiments 6 th edition. page 93 www.themegallery.com
Denatured by high temperature and pH.
Speed up the chemical reactions.
Lowers the activation energy (Ea).
103 108 times faster than uncatalyzed reactions
What is activation
energy ?
Every chemical reaction between molecules
involves bond breaking and bond forming.
The initial energy needed to start a chemical
reaction is called the free energy of activation, or
activation energy (EA).
Activation energy is often supplied in the form ofheat from the surroundings
Lowering the activation
energy (EA) barrier
necessary to initiate a
chemical reaction
How do enzymes work?
Progress of the reaction
Products
Reactants
G< O
Transition state
EA
Progress of the reaction
Products
Reactants
G is unaffectedby enzyme
Course ofreactionwithoutenzyme
EAwithoutenzyme EAwith
enzymeis lower
Course ofreactionwith enzyme
The reactant that an enzyme acts on is called the
enzymessubstrate.
The active site is the region on the enzyme where
the substrate binds.
In an enzymatic reaction, the substrate binds to
the active site of the enzyme
Forming an enzyme-substrate complex.
Copyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
MECHANISM OF ENZYME ACTION
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Fig. 8-16
Substrate
Active site
Enzyme Enzyme-substratecomplex
(b)(a)
In an enzymatic reaction, the substrate binds to
the active site of the enzyme. The active site can lower an EA barrier by :
Orienting substrates correctly
Straining substrate bonds
Providing a favorable microenvironment
Covalently bonding to the substrate
Catalysis in the Enzymes Active Site
(Campbell. Biology 9th edition. International edition. Page 200 201)
Figure 8.15-1
Substrates
Substrates enter active site.
Enzyme-substratecomplex
Substrates are heldin active site by weakinteractions.
12
Enzyme
Activesite
Figure 8.15-2
Substrates
Substrates enter active site.
Enzyme-substratecomplex
Substrates are heldin active site by weakinteractions.
Active site canlower EA and speedup a reaction.
12
3
Substrates areconverted toproducts.
4
Enzyme
Activesite
Figure 8.15-3
Substrates
Substrates enter active site.
Enzyme-substratecomplex
Enzyme
Products
Substrates are held
in active site by weakinteractions.
Active site canlower EA and speedup a reaction.
Activesite is
availablefor two new
substratemolecules.
Products arereleased.
Substrates areconverted toproducts.
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45
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www.themegallery.com
Two Hypotheses:
i. Model Lock and Key
ii. Model Induced Fit
MECHANISM OF ENZYME ACTION
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Lock :Enzyme (active site)
molecule. Key : Substrate .
Substrates molecule (key)
shape is complementary
with active site of the
enzyme (lock) molecule.
Substrate fits accurately into
a rigid active site of the
enzyme molecule.
LOCK AND KEY MODEL
Forming enzyme-substrate complex .
Product no longer fit into the active site. Leave the active site free to receive further
substrate molecule
LOCK AND KEY MODEL
www.themegallery.com
MECHANISM OF ENZYME ACTIONLOCK AND KEY MODEL
Source: http://www.flatworldknowledge.com
www.themegallery.com
INDUCED-FIT MODEL
Active site (enzyme)is able to change its shape
( flexible)to enfold a substrate molecule.
Distorted enzyme molecule in turn distorts the
substrate molecule.
Straining or twisting the bonds.
Substrates less stable and thus lowering EA.
www.themegallery.com
INDUCED-FIT MODEL
Products are formed which no longer bind to
active site and so move away.
Enzyme returns to its original shape.
Ready to bind the next substrate molecule.
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Conclusion
What are enzymes?
Globular protein (3D-shape).
Organic catalyst.
State the properties of enzymes.
Specificity.
Denatured.
Small amounts required.
Not damaged (Reused) by its reaction.
Conclusion
What is activation energy?
EA How do enzymes work?
Lowering EA
How the active site can lower the activation energy
barrier?
Refer to Campbell. Biology 9th edition.page 200- 201.
State mechanism of enzyme action.
Lock and Key Model
Induced-Fit Model
Explain the factors that affect the
enzymatic reaction.
Cofactors
Next Lecture
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