ENZYMESENZYMES

Enzyme IntroductionEnzyme Introduction► Enzymes are biological Enzymes are biological

catalysts that catalysts that lower the lower the activation energyactivation energy of of a reaction and in doing a reaction and in doing so, increase the rate of so, increase the rate of the reaction.the reaction.

► Most enzymes are Most enzymes are proteinsproteins..

► The name of an The name of an enzyme often ends in –enzyme often ends in –ase.ase. Ex. Amylase (breaks Ex. Amylase (breaks

down starch)down starch) Ex. Maltase (breaks down Ex. Maltase (breaks down

maltose)maltose)

Enzyme IntroductionEnzyme Introduction

► Enzymes catalyze over 4,000 reactionsEnzymes catalyze over 4,000 reactions► Each enzyme works only with a specific reactant called Each enzyme works only with a specific reactant called

the the substratesubstrate..► Enzymes work best under an optimal range of pH and Enzymes work best under an optimal range of pH and

temperature. Outside of this range they will denature.temperature. Outside of this range they will denature.

Enzyme-Substrate InteractionEnzyme-Substrate Interaction

► The substrate will bind to the The substrate will bind to the active siteactive site of the enzyme (a of the enzyme (a pocket or groove in 3D pocket or groove in 3D structure). structure).

► There is only one active site on There is only one active site on an enzyme. an enzyme.

► Enzyme-substrate complexEnzyme-substrate complex: : an enzyme with its substrate an enzyme with its substrate attached to the active site.attached to the active site.

► The enzyme may have an The enzyme may have an allosteric siteallosteric site as well where as well where inhibitors or activators will inhibitors or activators will bind.bind.

Enzyme-Substrate Enzyme-Substrate InteractionInteraction

Lock and Key ModelLock and Key Model► In 1894, Emil Fischer In 1894, Emil Fischer

suggested that the suggested that the enzyme and substrate enzyme and substrate have complimentary have complimentary geometric shapes and geometric shapes and fit into each other like fit into each other like a key into a lock.a key into a lock.

► The model explained The model explained enzyme specificity but enzyme specificity but not the stabilization of not the stabilization of the transition state, the transition state, the state between the the state between the substrate and the substrate and the products.products.

Induced-Fit ModelInduced-Fit Model► In 1958, Daniel Koshland modified the lock and key model.In 1958, Daniel Koshland modified the lock and key model.► His His Induced-fit model Induced-fit model states that the substrate causes the states that the substrate causes the

enzyme to change its shape to better hold the substrate.enzyme to change its shape to better hold the substrate.► Active sites were seen as ‘flexible’ and not rigid structures Active sites were seen as ‘flexible’ and not rigid structures

like before.like before.

ActivationActivation

►Some enzymes require a molecule known Some enzymes require a molecule known as an as an activatoractivator to attach to their to attach to their allosteric allosteric sitesite in order for their active site to be in order for their active site to be receptive to substrate.receptive to substrate.

InhibitionInhibition

► Inhibition is when the enzyme’s active Inhibition is when the enzyme’s active site is prevented from binding to a site is prevented from binding to a substrate.substrate.

►There are many different types of There are many different types of inhibition.inhibition.

Competitive InhibitionCompetitive Inhibition

►Competitive Competitive Inhibitors:Inhibitors: an an inhibitor competes inhibitor competes with the substrate for with the substrate for access to the active access to the active site of the enzyme.site of the enzyme.

animation

Non-competitive InhibitionNon-competitive Inhibition

►Noncompetitive Noncompetitive InhibitorsInhibitors: : substances that substances that attach to the attach to the allosteric site and allosteric site and change the shape of change the shape of the active site to the active site to prevent the prevent the substrate from substrate from binding to it.binding to it.

Feedback InhibitionFeedback Inhibition

►When enzyme-catalyzed reactions When enzyme-catalyzed reactions occur in a sequence, feedback occur in a sequence, feedback inhibition is when the product(s) of one inhibition is when the product(s) of one reaction allosterically inhibits an reaction allosterically inhibits an enzyme of a previous reaction.enzyme of a previous reaction.

animation

Inhibition by LocationInhibition by Location

►Location: restricting the location of enzymes to Location: restricting the location of enzymes to certain locations within the cell helps to certain locations within the cell helps to regulate activityregulate activity incorporation into specific organelle incorporation into specific organelle

membranes or fluid-filled spaces (cytoplasm / membranes or fluid-filled spaces (cytoplasm / inside organelles)inside organelles)

Industrial Uses of EnzymesIndustrial Uses of Enzymes

Rate of Enzyme ActivityRate of Enzyme Activity► An increase in An increase in temperaturetemperature

increases the rate of reaction. increases the rate of reaction. However, when an enzyme is However, when an enzyme is involved, if the temperature involved, if the temperature reaches beyond a critical reaches beyond a critical point, denaturation may occur point, denaturation may occur and since the enzyme is not and since the enzyme is not functioning the reaction will functioning the reaction will slow down. (Body enzymes slow down. (Body enzymes optimal: 37 degrees C) optimal: 37 degrees C)

► Altering the pH may also alter Altering the pH may also alter the effectiveness of the the effectiveness of the enzyme, as most have an enzyme, as most have an optimum pH (Ex. digestive optimum pH (Ex. digestive enzymes) enzymes)

Rate of Enzyme ActivityRate of Enzyme Activity

► Limiting FactorLimiting Factor: The number of enzymes can be a : The number of enzymes can be a limiting factor when the amount of substrate is limiting factor when the amount of substrate is increased, it takes time to catalyze a reaction; the increased, it takes time to catalyze a reaction; the enzymes become enzymes become saturated.saturated.

► Some enzymes need other components before they Some enzymes need other components before they work properly:work properly: Cofactors:Cofactors: nonprotein components that bind to nonprotein components that bind to

the enzyme active site or the substrate to help the enzyme active site or the substrate to help the enzyme.the enzyme.

CoenzymesCoenzymes: these compounds often shuttle : these compounds often shuttle molecules from one enzyme to another.molecules from one enzyme to another.