chapter 14 biocatalysis hour1

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 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



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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3

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


MECHANISM OF ENZYME ACTIONLOCK AND KEY MODEL

Source: http://www.flatworldknowledge.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.


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

chapter 14 biocatalysis hour1

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