Menu1

CH. 6 Factors CH. 6 Factors Affecting ENZYME Affecting ENZYME

ActivityActivity

Menu2

Catabolic and Anabolic Catabolic and Anabolic ReactionsReactions The energy-producing reactions within cells

generally involve the breakdown of complex organic compounds to simpler compounds. These reactions release energy and are called catabolic reactions.

Anabolic reactions are those that consume energy while synthesizing compounds.

ATP produced by catabolic reactions provides the energy for anabolic reactions. Anabolic and catabolic reactions are therefore coupled (they work together) through the use of ATP.

Diagram: next slide

ATP ADP + Pi

Energy

Energy

Menu

An anabolic reaction

A catabolic reaction

Catabolic and Anabolic Reactions

Menu4

Enzymes Lower Activation Enzymes Lower Activation EnergyEnergy

Ene

rgy

Sup

plie

dE

nerg

y R

elea

sed

Activation energy without enzyme

Activation energywith enzyme

Enzymes lower the amount of activation energy needed for a reaction.

Menu

Substrate

Enzyme

Active Site

Enzyme-Substrate ComplexProduct

Enzyme

1

23

EnzymesEnzymes

Enzymes are organic catalysts.

Menu

Cofactor/Coenzyme

Menu6

EnzymesEnzymes

Catalysts are substances that speed up chemical reactions.  Organic catalysts (contain carbon) are called enzymes.

Enzymes are specific for one particular reaction or group of related reactions.

Many reactions cannot occur without the correct enzyme present.

They are often named by adding “ASE" to the name of the substrate. Example: Dehydrogenases are enzymes that remove hydrogen.

Menu7

Induced Fit Theory – Most Induced Fit Theory – Most currentcurrent An enzyme-substrate complex forms

when the enzyme’s active site binds with the substrate like a key fitting a lock.

The substrate molecule does not fit exactly in the active site. This induces a change in the enzymes conformation (shape) to make a closer fit.

After the reaction, the products are released and the enzyme returns to its normal shape.

Only a small amount of enzyme is needed because they can be used repeatedly.

Menu8

Rate of ReactionRate of Reaction

Reactions with enzymes are up to 10 billion times faster than those without enzymes.

Enzymes typically react with between 1 and 10,000 molecules per second. Fast enzymes catalyze up to 500,000 molecules per second.

Substrate concentration, enzyme concentration, Temperature, and pH  affect the rate of enzyme reactions.

Menu9

Substrate ConcentrationSubstrate Concentration At lower concentrations, the active sites on most of the

enzyme molecules are not filled because there is not much substrate.  Higher concentrations cause more collisions between the molecules.  With more molecules and collisions, enzymes are more likely to encounter molecules of reactant.

The maximum velocity of a reaction is reached when the active sites are almost continuously filled. Increased substrate concentration after this point will not increase the rate.  Reaction rate therefore increases as substrate concentration is increased but it levels off.

Substrate Concentration

Rat

e of

Rea

ctio

nEnzyme Active Site is Saturated

Menu10

Enzyme ConcentrationEnzyme Concentration If there is insufficient enzyme present, the reaction

will not proceed as fast as it otherwise would because there is not enough enzyme for all of the reactant molecules.

As the amount of enzyme is increased, the rate of reaction increases. If there are more enzyme molecules than are needed, adding additional enzyme will not increase the rate. Reaction rate therefore increases as enzyme concentration increases but then it levels off.

Enzyme Concentration

Rat

e of

Rea

ctio

n

Even when adding more enzymes, there isn’t any more available substrate to create product at a faster rate

Menu11

Effect of Temperature on Effect of Temperature on Enzyme ActivityEnzyme Activity

30 40 50

Rat

e of

Rea

ctio

n

Temperature

Menu12

Effect of Temperature on Effect of Temperature on Enzyme ActivityEnzyme Activity

30 40 50

Rat

e of

Rea

ctio

n

Temperature

Increasing the temperature causes more collisions between substrate and enzyme molecules. The rate of reaction therefore increases as temperature increases.

Menu13

Effect of Temperature on Effect of Temperature on Enzyme ActivityEnzyme Activity

30 40 50

Rat

e of

Rea

ctio

n

Temperature

Enzymes denature when the temperature gets too high. The rate of reaction decreases as the enzyme becomes nonfunctional.

Menu14

TemperatureTemperature Higher temperature causes more collisions between the

atoms, ions, molecules, etc. It therefore increases the rate of a reaction – “Turnover Rate”. More collisions increase the likelihood that substrate will collide with the active site of the enzyme.

Above a certain temperature, activity begins to decline because the enzyme begins to denature (unfold).

The rate of chemical reactions therefore increases with temperature but then decreases.

30 40 50

Rat

e of

Rea

ctio

n

Temperature

Menu15

DenaturationDenaturation If the hydrogen bonds within an enzyme are broken, the

enzyme may unfold or take on a different shape. The enzyme is denatured.

A denatured enzyme will not function properly because the shape of the active site has changed.

If the denaturation is not severe, the enzyme may regain its original shape and become functional.

The following will cause denaturation:– Heat– Changes in pH– Heavy-metal ions (lead, arsenic, mercury)– Alcohol– UV radiation

Menu16

Effect of pH on Enzyme Effect of pH on Enzyme ActivityActivity

2 3 4 5 6 7 8 9

Rat

e of

Rea

ctio

n

pH

Pepsin Trypsin

Each enzyme has its own optimum pH.

Menu17

pHpH

Each enzyme has an optimal pH. Pepsin, an enzyme found in the stomach, functions best at a low pH. Trypsin, found in the intestine, functions best at a neutral pH.

A change in pH can alter the ionization of the R groups of the amino acids. When the charges on the amino acids change, hydrogen bonding within the protein molecule change and the molecule changes shape. The new shape may not be effective.

The diagram shows that pepsin functions best in an acid environment. This makes sense because pepsin is an enzyme that is normally found in the stomach where the pH is low due to the presence of hydrochloric acid. Trypsin is found in the duodenum (small intestine), and therefore, its optimum pH is in the neutral range to match the pH of the duodenum.

2 3 4 5 6 7 8 9

Rat

e of

Rea

ctio

n

pH

Pepsin Trypsin

Menu18

Metabolic PathwaysMetabolic Pathways

Metabolism refers to the chemical reactions that occur within cells.

Reactions occur in a sequence and a specific enzyme catalyzes each step.

Menu19

Metabolic PathwaysMetabolic Pathways

enzyme 1 enzyme 2 enzyme 3 enzyme 4

Fenzyme 5

A B C D E

Enzymes are very specific. In this case enzyme 1 will catalyze the conversion of A to B only.

Notice that C can produce either D or F. This substrate has two different enzymes that work on it.

Menu20

A Cyclic Metabolic PathwayA Cyclic Metabolic Pathway

B

C

D

F

A

E

A + F B

B C D

D F + E

In this pathway, substrate “A” enters the reaction. After several steps, product “E” is produced.

Menu21

Regulation of EnzymesRegulation of Enzymes

The next several slides illustrate how cells regulate enzymes. For example, it may be necessary to decrease the activity of certain enzymes if the cell no longer needs the product produced by the enzymes.

Menu22

Regulation of EnzymesRegulation of Enzymes

geneticregulation

regulation of enzymesalready produced

competitiveinhibition

noncompetitiveInhibition

(next slide)

Cell can turn on DNA genes to build more enzymes when needed

Cells can use certain chemicals to slow down existing enzymes

Menu23

Competitive InhibitionCompetitive Inhibition

In competitive inhibition, a similar-shaped molecule competes with the substrate for active sites.

Menu24

Competitive InhibitionCompetitive Inhibition

Active site is being occupied by competitive inhibitor

This substrate cannot get into active site at this time

Menu25

Noncompetitive InhibitionNoncompetitive Inhibition

Another form of inhibition involves an inhibitor that binds to an allosteric site of an enzyme.  An allosteric site is a different location than the active site.

The binding of an inhibitor to the allosteric site alters the shape of the enzyme, resulting in a distorted active site that does not function properly.

Active site Inhibitor Altered active site

Enzyme

Menu26

Noncompetitive InhibitionNoncompetitive Inhibition

The binding of an inhibitor to an allosteric site is usually temporary.   Poisons are inhibitors that bind irreversibly. For example, penicillin inhibits an enzyme needed by bacteria to build the cell wall. Bacteria growing (reproducing) without producing cell walls eventually rupture.

Menu27

Enzyme regulation by negative feedback inhibition is similar to the thermostat example. As an enzyme's product accumulates, it turns off the enzyme just as heat causes a thermostat to turn off the production of heat.

Feedback InhibitionFeedback Inhibition

A B C Denzyme 1 enzyme 2 enzyme 3

The goal of this hypothetical metabolic pathway is to produce chemical D from A.

B and C are intermediates.

The next several slides will show how feedback inhibition regulates the amount of D produced.

Menu28

Feedback InhibitionFeedback Inhibition

A B C Denzyme 1 enzyme 2 enzyme 3X

Enzyme 1 is structured in a way that causes it to interact with D. When the amount of D increases, the enzyme stops functioning.

X

The amount of B in the cell will decrease if enzyme 1 is inhibited.

X X

C and D will decrease because B is needed to produce C and C is needed to produce D.

Menu29

A B C DX

Feedback InhibitionFeedback Inhibition

enzyme 1 enzyme 2 enzyme 3X X

When the amount of D drops, enzyme 1 will no longer be inhibited by it.

B C D

B, C, and D can now be synthesized.

Menu30

Feedback InhibitionFeedback Inhibition

A B C Denzyme 1 enzyme 2 enzyme 3X

As D begins to increase, it inhibits enzyme 1 again and the cycle repeats itself.

Menu31

The EndThe End