1

Amino Acids, Proteins, and Enzymes

Enzymes

Enzyme Action

Factors Affecting Enzyme Action

Enzyme Inhibition

2

Program Objectives

List 6 common features of enzyme action.

Describe the role of the active site.

Draw an energy diagram and identify the substrates, products, activated complex and activation energy.

Describe and explain the sensitivity of enzymes to heat and pH.

Identify mechanisms by which an enzyme may reduce the activation energy for a reaction.

3

Enzymes are the working unit of an organism. Every chemical reaction that occurs in an organism is made possible by a specific enzyme.

A cup of sugar left undisturbed for twenty years changes very little. However when you eat sugar, it rapidly undergoes chemical change. EnzymesEnzymes account for the differences in the rate of change

4

Enzymes

• Catalysts for biological reactions• Most are proteins• Lower the activation energy• Increase the rate of reaction• Activity lost if denatured• May be simple proteins• May contain cofactors such as metal ions

or organic (vitamins)

5

Proteins that catalyze (Speed up) reactions.

6

Energy of Activation is necessary to convert the molecule to its

products.

Potential Energy

7

Enzymes lower activation energy increasing the rate of

the reaction.

8

Ways enzymes speed reactions

*increase the frequency of successful collisions

*improve the orientation between colliding substrates

*provide a new reaction path with a lower activation energy– Warp and weaken a bond– Provide a favorable electronic environment

weakening bond

9

Enzymes are sensitive to environmental change.

– temperature• changes shape of active site

– pH• changes shape of active site

– enzyme concentration– substrate concentration– inhibitors

10

Cofactors:An ion or molecule that must be

associated with an enzyme for the enzyme’s proper functioning.

Several large organic molecules, called coenzymes, serve as

cofactors.

FAD, NAD & NADP, are examples.

11

Name of Enzymes

• End in –ase• Identifies a reacting substance

sucrase – reacts sucroselipase - reacts lipid

• Describes function of enzymeoxidase – catalyzes oxidationhydrolase – catalyzes hydrolysis

• Common names of digestion enzymes still use –inpepsin, trypsin

12

Learning Check E1

Match the type of reaction with the enzymes:

(1) aminase (2) dehydrogenase

(3) Isomerase (4) synthetase

A. Converts a cis-fatty acid to trans.

B. Removes 2 H atoms to form double bond

C. Combine two molecules using ATP

D. Adds NH3

13

Enzyme Action: Lock and Key Model

• An enzyme binds a substrate in a region called the active site

• Only certain substrates can fit the active site• Amino acid R groups in the active site help substrate

bind• Enzyme-substrate complex forms• Substrate reacts to form product• Product is released

14

15

Lock and Key Model

+ +

E + S ES complex E + P

S

P

P

S

16

Enzyme Action: Induced Fit Model

• Enzyme structure flexible, not rigid• Enzyme and active site adjust shape to

bind substrate• Increases range of substrate specificity• Shape changes also improve catalysis

during reaction

17

The binding of the substrate to the enzyme alters the structure of the enzyme, placing some strain on the substrate and further facilitating the reaction

18

Enzyme Action: Induced Fit Model

E + S ES complex E + P

S

P

P

SS

19

Learning Check E2

A. The active site is(1) the enzyme(2) a section of the enzyme(3) the substrate

B. In the induced fit model, the shape of the enzyme when substrate binds(1) Stays the same(2) adapts to the shape of the substrate

20

Solution E2

A. The active site is

(2) a section of the enzyme

B. In the induced fit model, the shape of the enzyme when substrate binds

(2) adapts to the shape of the substrate

21

Factors Affecting Enzyme Action: Temperature

• Little activity at low temperature• Rate increases with temperature• Most active at optimum temperatures

(usually 37°C in humans)• Activity lost with denaturation at high

temperatures

22

Factors Affecting Enzyme ActionOptimum temperature

ReactionRate

Low High

Temperature

23

Factors Affecting Enzyme Action: Substrate Concentration

• Increasing substrate concentration increases the rate of reaction (enzyme concentration is constant)

• Maximum activity reached when all of enzyme combines with substrate

24

Factors Affecting Enzyme Action

Maximum activity

Reaction

Rate

substrate concentration

25

Factors Affecting Enzyme Action: pH

• Maximum activity at optimum pH• R groups of amino acids have proper

charge• Tertiary structure of enzyme is correct• Narrow range of activity• Most lose activity in low or high pH

26

Factors Affecting Enzyme Action

Reaction

Rate

Optimum pH

3 5 7 9 11

pH

27

Learning Check E3

Sucrase has an optimum temperature of 37°C and an optimum pH of 6.2. Determine the effect of the following on its rate of reaction

(1) no change (2) increase (3) decrease

A. Increasing the concentration of sucrose

B. Changing the pH to 4

C. Running the reaction at 70°C

28

Solution E3

Sucrase has an optimum temperature of 37°C and an optimum pH of 6.2. Determine the effect of the following on its rate of reaction

(1) no change (2) increase (3) decrease

A. 2, 1 Increasing the concentration of sucrose

B. 3 Changing the pH to 4

C. 3 Running the reaction at 70°C

29

Enzyme Inhibition

Inhibitors • cause a loss of catalytic activity• Change the protein structure of an enzyme• May be competitive or noncompetitive• Some effects are irreversible

30

Competitive Inhibition

A competitive inhibitor• Has a structure similar to

substrate• Occupies active site• Competes with substrate for

active site• Has effect reversed by increasing

substrate concentration

31

Noncompetitive Inhibition

A noncompetitive inhibitor• Does not have a structure like substrate• Binds to the enzyme but not active site• Changes the shape of enzyme and active

site• Substrate cannot fit altered active site• No reaction occurs• Effect is not reversed by adding substrate

32

Effect of Inhibitors

33

Effect of Activators

34

Learning Check E4

Identify each statement as describing an inhibitor that is

(1) Competitive (2) Noncompetitive

A. Increasing substrate reverses inhibition

B. Binds to enzyme, not active site

C. Structure is similar to substrate

D. Inhibition is not reversed with substrate

35

Solution E4

Identify each statement as describing an inhibitor that is

(1) Competitive (2) Noncompetitive

A. 1 Increasing substrate reverses inhibition

B. 2 Binds to enzyme, not active site

C. 1 Structure is similar to substrate

D. 2 Inhibition is not reversed with substrate

36

Active Site Summary

*is usually a crevice or pocket on the protein

*formed with only a few of the enzymes amino acids

*changes its shape in response to the substrate

37

The active site is a region where an enzyme molecule is folded in the shape of a crevice or

cleft and where a particular reaction is catalyzed

38

The substrate is a specific molecules that an enzyme can chemically recognize, bind to

briefly, and modify in a specific way.

39

Enzymes are specific – only catalyzes one reaction

Active site is complementary shape

to the substrate affected.

40

Reaction Specificity

An enzyme always puts out the same kind of product when fed a given substrate.

41

Enzymes perform simple reactions.

isomerization – rearrangement of molecules

exchange – transfer of atoms

addition – put two substrates together

decomposition – change substrate into two products.

42

Things enzymes do NOT do.

*Enzymes don’t make anything happen that would not eventually happen on its own, They just make it happen faster -- at least a million times faster, usually. *Enzymes do NOT initiate the reaction.*Enzymes do NOT Provide energy.– LIGHT provides activation energy– OR INETIC ENERGY is the activation

energy.

43

*Enzymes are not used up in a chemical reaction.

*Enzymes do have a working lifetime and eventually do break down.

*Enzymes are not permanently altered in a reaction.

44

7. The enzyme is NOT changed in the reaction.

45

Allosteric Regulators

46

Commercial Uses of EnzymesSome Non-Food Enzyme Uses

Proteases

Detergent Laundry Aid

Environmental Reduction of proteins in sewage treatment

photography Recovery of silver from scrap film

Glucose Oxidase

Clinical-Analytical

Diabetes test (glucose)

Enzyme Industry Purpose or Action