Enzymes:

The Biological Catalysts

Energy of Activation

• Most reactions do not start spontaneously

• They require energy, such as a spark, to get started.

• This is called activation energy

2

Energy of Activation

• The energy used

to break the

bonds in the

reactants so they

can be reformed

in the products is

called the energy

of activation.

3

Enzymes

• Enzymes are biological catalysts that increase

the reaction rate of biochemical reactions.

4

Characteristics of

enzymes

A. Made of proteins (or

RNA).

B.They are very specific

and only work with a

certain set of reactants

or substrates that fit on

their active site. The enzyme shown is lysozyme

Induced Fit

C. Enzymes can be used over and over again.

D. When an enzyme binds with the substrate, the

bonded substrate interacts with the enzyme

causing it to change shape. This change in

shape facilitates the chemical reaction to occur.

This is called the induced fit.

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Enzyme Example Ribonuclease

• Ribonuclease

decomposes RNA,

and the nucleotides

can be recycled.

• The purple part is the

enzyme; the green

part is the substrate

(RNA).

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Enzymes Work by Lowering the Energy

of Activation

E. Enzymes increase the reaction rate by

lowering the energy of activation.

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The Enzyme Sucrase Decomposing

Sucrose

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Initial Velocity

• The reaction rate of an enzymatic reaction is always

fastest at the beginning because plenty of substrate

is available.

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Effects on Reaction Rates

10

Temperature increases enzyme action until the

enzyme protein is denatured

Effect on Reaction Rates

11

Most enzymes work best with a pH of 7, but

some can work in other ranges before denaturing

Effect onReaction Rates

12

Competitive Inhibitors block enzyme activity by

mimicking the substrate

Effect of Noncompetitive Inhibitors and

Enzymatic Reaction Rates

13

Noncompetitve inhibitors block enzyme function

too, but attach a different point than the active site

Draw and Label Activation Energy

Diagram

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Reactions to Know

• Hydrolysis Rxn – breaks apart a compound by

adding a water molecule

• Dehydration Synthesis Rxn – links two compouunds

by creating and releasing a water molecule

• Endergonic Rxn – a reaction that requires

energy

• Exergonic Rxn – a reaction that releases

energy

• Redox Rxn – a reaction that involves

transferring electrons 15