Chapter 14 Biocatalysis Hour2

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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+)


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.


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)


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

Chapter 14 Biocatalysis Hour2

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