EnzymesEnzymes

Question:Question:

• What are enzymesenzymes?

EnzymesEnzymes

Answer:Answer:

1.1. Proteins:Proteins: most enzymesenzymes are proteinsproteins, primarily tertiarytertiary and quaternary quaternary structuresstructures..

2.2. Catalyst:Catalyst: chemical agentchemical agent that acceleratesaccelerates a reaction without being permanently changed in the process.

EnzymesEnzymes

3.3. Selective:Selective: enzymes are specific for which they will catalyzecatalyze (Specificity - (Specificity -

depends depends upon 3D shape).upon 3D shape).

4.4. Recycled:Recycled: enzymes are reusable.

5.5. “ase”“ase” endings: examples:examples: sucrasesucrase

maltasemaltase

lactaselactase

Question:Question:

• How do enzymesenzymes work?

EnzymesEnzymes

Answer:Answer:

• EnzymesEnzymes speed up the cell’s chemical reactions by lowering the free energy of activationlowering the free energy of activation.

EnzymesEnzymes

FreeEnergy

Progress of the reaction

Reactants

Products

Free energy of activationFree energy of activation

Without Enzyme

With Enzyme

SubstrateSubstrate

• The substancesubstance (reactant) an enzymeenzyme acts on.

Enzyme

Substrate

Active SiteActive Site

• A restricted regionrestricted region of an enzymeenzyme molecule which bindsbinds to the substratesubstrate.

Enzyme

Active Site

Substrate

Induced FitInduced Fit

• A changechange in the configurationconfiguration of an enzyme’senzyme’s active siteactive site (H and ionic bonds are involved).

• InducedInduced by the substratesubstrate..

Enzyme

Active Sitesubstrate

induced fit

Enzymatic ReactionEnzymatic Reaction

substrate (sucrose)substrate (sucrose) + enzyme (sucrase) enzyme (sucrase)

enzymeenzyme--substratesubstrate complex complex

and +sucrasesucrase

glucoseglucose fructosefructose

productsproducts + + enzymeenzyme

E + S ES E + P

What Affects Enzyme Activity?What Affects Enzyme Activity?

• Three factors:Three factors:

1.1. Environmental ConditionsEnvironmental Conditions

2.2. Cofactors and CoenzymesCofactors and Coenzymes

3.3. Enzyme InhibitorsEnzyme Inhibitors

1. Environmental Conditions1. Environmental Conditions• Enzymatic reactionsEnzymatic reactions are very specific. The following

environmental conditionsenvironmental conditions affect enzymatic reactions: (Non-specific Inhibitors)

1.1. Temperature Temperature (extremes most dangerous):(extremes most dangerous):

- high temps - high temps may denature denature the enzyme.enzyme.

2.2. pH (most like 6 - 8 pH - neutral) acid/basepH (most like 6 - 8 pH - neutral) acid/base

3.3. Ionic concentration (salt ions)Ionic concentration (salt ions)

4.4. Alcohol (disinfectants)Alcohol (disinfectants)

5.5. Heavy Metals (Silver nitrate)Heavy Metals (Silver nitrate)

6. Reducing agents (Break S-S bonds)6. Reducing agents (Break S-S bonds)

2. Cofactors and Coenzymes2. Cofactors and Coenzymes

• Cofactors-Inorganic substances (zinc, iron) Cofactors-Inorganic substances (zinc, iron) also called minerals.

• Coenzymes- organic substances not proteins also called Vitamins

• Both are sometimes needed for proper enzymatic enzymatic activityactivity.

• Example:Example:

IronIron must be present in the quaternary quaternary structurestructure -- hemoglobinhemoglobin in order for it to pick up oxygen.

3. Enzyme Inhibitors3. Enzyme Inhibitors

• Two examples:Two examples:

a.a. Competitive inhibitors:Competitive inhibitors: are chemicals that resembleresemble an enzyme’s normal substrateenzyme’s normal substrate and competecompete with it for the active siteactive site.

Enzyme

Competitive inhibitor

Substrate

3. Enzyme Inhibitors3. Enzyme Inhibitors

b.b. Noncompetitive inhibitors:Noncompetitive inhibitors:

Inhibitors that do not enter the active sitedo not enter the active site, but bind to another partbind to another part of the enzymeenzyme

causing the enzymeenzyme to change its shapechange its shape, which in turn alters the active sitealters the active site.

Substrate Enzyme

active site altered

NoncompetitiveInhibitor

Non-competitive cont.• Non-competitive inhibition is irreversible• They can bond at, near , or remote from the

active site– Also called Allosteric Regulation (inhibitor binds away

from active site)

– Means “other site”

– Nerve gases

Naming of Enzymes

– mostly historical :  substrate + "ase"

• Remember Chitinase, Amylase, Cellulase?

• Sucrase breaks sucrose into glucose and fructose

• Also based on type of reaction

Common Enzymes

• Transferases catalyze the transfer of functional groups

• Hydrolyases catalyze hydrolysis - adds water across C-C bonds

• Lyases add or remove functional groups to form C=C bonds

• Isomerases catalyze isomerizations - change from one isomer to another

• Ligases  condensation of 2 substrates