enzymes. enzymes are catalysts catalytic proteins: change the rate of reactions w/o being consumed ...

ENZYMESENZYMES

Enzymes are CatalystsEnzymes are Catalysts Catalytic proteinsCatalytic proteins: change : change

the rate of reactions w/o the rate of reactions w/o being consumedbeing consumed

Enzymes speed up Enzymes speed up reactions by lowering the reactions by lowering the activation energyactivation energy

Activation energy (free Activation energy (free energy of activation) = the E energy of activation) = the E required to break bondsrequired to break bonds

Activation E must be Activation E must be reached for reaction to reached for reaction to progressprogress

What’s going on?What’s going on? SubstrateSubstrate: enzyme : enzyme

reactantreactant Active siteActive site: pocket : pocket

or groove on or groove on enzyme that binds enzyme that binds to substrateto substrate

Induced fit modelInduced fit model Substrate fits into Substrate fits into

the enzyme which the enzyme which wraps around itwraps around it

How does it work?How does it work?

Enzymes lower AE by:Enzymes lower AE by: Bring together in proper orientationBring together in proper orientation Physical stress- bending or stretching of Physical stress- bending or stretching of

chemical bondschemical bonds Increased reactivity due to environment Increased reactivity due to environment

(charge, pH, etc. within active site)(charge, pH, etc. within active site) Activity of substrate directly w/ enzymeActivity of substrate directly w/ enzyme

Effects on Enzyme Effects on Enzyme ActivityActivity

TemperatureTemperature pHpH Cofactors:Cofactors:

inorganic, nonprotein inorganic, nonprotein helpers; ex.: zinc, iron, helpers; ex.: zinc, iron, coppercopper

Coenzymes:Coenzymes:organic helpers; ex.: organic helpers; ex.: vitaminsvitamins

Enzyme InhibitorsEnzyme Inhibitors

Irreversible (covalent); Irreversible (covalent); reversible (weak bonds)reversible (weak bonds)

CompetitiveCompetitive: competes for : competes for active site (reversible); active site (reversible); mimics the substratemimics the substrate

NoncompetitiveNoncompetitive: bind to : bind to another part of enzyme another part of enzyme (allosteric site) altering its (allosteric site) altering its conformation (shape)conformation (shape)

poisons, toxins, antibioticspoisons, toxins, antibiotics

Allosteric RegulationAllosteric Regulation

Not all chemical Not all chemical processes occur at the processes occur at the same timesame time Enzymes can be activated Enzymes can be activated

when needed and inhibited when needed and inhibited when they’re notwhen they’re not

Allosteric activators and Allosteric activators and inhibitors bind to turn the inhibitors bind to turn the enzyme complex on or offenzyme complex on or off

Cooperativity- substrate Cooperativity- substrate must be bound to activate must be bound to activate enzyme enzyme

Feedback InhibitionFeedback Inhibition

End product of End product of reaction binds to reaction binds to allosteric site of allosteric site of enzyme to stop enzyme to stop further productionfurther production

Like a thermostatLike a thermostat