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EnzymesEnzymes

Chemical Reactions

• Reactions begin with reactants and result in products

Reactants Product

CO2 + H20 H2CO3

• Chemical reactions always involve changes in the chemical bonds that join atoms in compounds.

Energy in Reactions

• Most chemical reactions require energy to get started.

• Chemists call the energy required to start a reaction “Activation Energy”

Catalysts and Enzymes

• A catalyst is a substance that speeds up chemical reactions.• Lighter Fluid is a catalyst for a

campfire.

• Enzymes are proteins that act as catalysts by speeding up chemical reactions that take place in cells.

Substrates

• Reactants that an enzyme works on are called substrates.

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What Are Enzymes?What Are Enzymes?• Most enzymes

are Proteins Proteins ((tertiary and quaternary structures)

• Act as CatalystCatalyst to accelerates a reaction

• Not permanentlyNot permanently changed in the process

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EnzymesEnzymes•Are specific

for what they will catalyzecatalyze

•Are ReusableReusable•End in –asease

-Sucrase-Sucrase-Lactase-Lactase-Maltase-Maltase

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How do enzymes Work?How do enzymes Work?

Enzymes work by weakening weakening bondsbonds which which lowers lowers activation activation energyenergy

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EnzymesEnzymes

FreeEnergy

Progress of the reaction

Reactants

Products

Free energy of activationFree energy of activation

Without Enzyme

With Enzyme

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Enzyme-Substrate ComplexEnzyme-Substrate ComplexThe substancesubstance

(reactant) an enzymeenzyme acts on is the substratesubstrate

EnzymeSubstrate Joins

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Active SiteActive Site• A restricted regionrestricted region of an enzymeenzyme

molecule which bindsbinds to the substratesubstrate.

EnzymeSubstrate

Active Site

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Induced FitInduced Fit•A change in the shapeshape of an enzyme’s active site

• Induced Induced by the substrate

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Induced FitInduced Fit

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

• InducedInduced by the substratesubstrate..

Enzyme

Active Sitesubstrate

induced fit

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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

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1. Environmental Conditions1. Environmental Conditions

1. Extreme1. Extreme Temperature Temperature are the are the most dangerousmost dangerous

- - high tempshigh temps may denature denature (unfold) (unfold) the enzyme. enzyme.

2.2. pHpH (most like 6 - 8 pH near (most like 6 - 8 pH near neutral)neutral)

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

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2. Cofactors and Coenzymes2. Cofactors and Coenzymes

• Inorganic substances Inorganic substances (zinc, iron)(zinc, iron) and vitaminsvitamins (respectively) are sometimes need for proper enzymatic activityenzymatic activity.

• Example:Example:IronIron must be present in the

quaternary quaternary structurestructure -- hemoglobinhemoglobin in order for it to pick up oxygen.pick up oxygen.

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Two examples of Enzyme Two examples of Enzyme InhibitorsInhibitors

a. Chemicals that block the enzyme

EnzymeCompetitive inhibitor

Substrate

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InhibitorsInhibitors

b.b. Noncompetitive inhibitorsNoncompetitive inhibitors::Inhibitors that do not enter thedo not enter the

active siteactive site, but bind tobind to another another partpart of the enzymeenzyme causing the enzymeenzyme to change its shapechange its shape, which in turn alters the alters the active siteactive site.

Enzymeactive site altered

NoncompetitiveInhibitor

Substrate

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