Enzyme Review

Enzymes are….Enzymes work by….Environmental factors that effect

enzyme activity are….

Enzymes are…ProteinsCatalysts for biological

reactions something that speeds up a reaction. Up to 1012 fold

Usually end in ‘…ase’. Name Identifies a reacting substance

sucrase – reacts sucroselipase - reacts lipid

Name describes function of enzymeoxidase – catalyzes oxidationhydrolase – catalyzes hydrolysis

Enzymes work by…• Lowering the

activation energy of a reaction.

• Increasing the rate of reaction.

Mechanism for enzyme action:Lock and Key Model

A substrate(s) fits into a binding site on the enzyme called the active site.

The enzyme lowers the energy required to reach the transition state.

The product(s) is/are produced.

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

Enzyme Action: Induced Fit Model

E + S ES complex E + P

S

P

P

SS

Factors Affecting Enzyme Action

Optimum temperature

ReactionRate

Low High Temperature

All enzymes have a temperature range within which they are most effective.

Denaturation

Factors Affecting Enzyme Action

Reaction

Rate

Optimum pH

3 5 7 9 11

pH

Enzyme Activity & pH: Digestive enzymes

Factors Affecting Enzyme Action

Maximum activity

Reaction

Rate

substrate concentration

• Enzyme cofactors• Vitamins• Phosphorylation May affect concen-tration and enzyme action.

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

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

Helps regulate the amount of product

Competitive Inhibition

Penicillin Mode of Action - Enzyme Inhibition:

All penicillin derivatives work by inhibiting proper bacterial cell wall synthesis. If cell walls are improperly made cell walls allow water to flow into the cell causing it to burst.

Noncompetitive Inhibition

A noncompetitive inhibitor

Does not have a structure like substrate

Binds to the enzyme but not active site; called the allosteric site (allo = other, steric = space)

Changes the shape of enzyme and active site

Substrate cannot fit altered active site

No reaction occurs

Effect is not reversed by adding substrate

Competitive vs. Noncompetitive Inhibition

Enzyme Inhibition

May be irreversible: inhibitor permanently inactivates or destroys the enzyme.

EX: poisonsCyanide is an inhibitor for the essential enzyme cytochrome c oxidase

Penicillin is poison to bacteria

Nerve gas inhibits acetylcholinesterase (necessary for proper nerve/muscle function).

And now a few thoughts about lab…

Liver = source of enzyme catalase

Hydrogen peroxide = substrate

Three different variables:

concentration temperature pH

Catalase Protects Cells by Destroying Hydrogen Peroxide

H2O2 is produced in the breakdown of fats and amino acids.

This occurs in an organelle called the peroxisome, which is also where catalase is found.

Catalase reduces the activation energy for the reduction of H202 86-foldH2O2 is extraordinarily reactive and will damage the cell.

2H2O2 2H2O + O2

H2O2 is extraordinarily reactive and will damage the cell.