ENZYMESENZYMES

OutlineOutline Review – What is an enzyme?

Models of enzyme activity◦ Lock and key◦ Induced fit model

Factors affecting enzyme activity◦ Temperature◦ pH

Regulation of enzyme activity◦ Inhibition◦ Allosterically◦ Feedback inhibition

What is an enzyme?What is an enzyme?

“Biological catalysts”: Speed up reactions in the body

What is a catalyst????What is a catalyst????a substance which increase in the rate of a

chemical reaction due to it’s participation.The effect of a catalyst may vary due to

the presence of other substances known as inhibitors or poisons (which reduce the catalytic activity)

Promoters (which increase the activity). The opposite of a catalyst, a substance

that reduces the rate of a reaction, is an inhibitor.

The antonym…The antonym…The opposite of a catalyst, a substance

that reduces the rate of a reaction, is an inhibitor.

Literacy T.Y.P. 5 minutes.Literacy T.Y.P. 5 minutes.List three synonyms and three antonyms

of a catalyst.Give an example of each.

Share with your peers.

Type of protein◦Polymer of amino acids

Often globular (spherical) in shape

Contain “active sites” – depressions or grooves on the surface where molecules can bind

Binding to an enzyme is very selective:◦Active sites interact with specific molecules to

catalyze specific reactions

The molecule that binds to an enzyme is called its “substrate”

Enzymes lower the activation energy required for a reaction to occur.◦Stabilizes the transition state by stretching the

bonds of the substrate

Some enzymes need to bind to additional molecules to function:◦Cofactors (usu. metal ions), or◦Coenzymes (act like shuttles btw. enzymes)

Apoenzyme – The enzyme, without its cofactors/coenzymes

Holoenzyme – The active form, bound to cofactors/coenzymes

MODELS OF ENZYME ACTIVITYMODELS OF ENZYME ACTIVITYLock and Key model

Induced fit model

The “Lock and Key” modelThe “Lock and Key” modelThe enzyme has an active site that is

unchangingSubstrates bind chemical process

occurs

Induced fit modelInduced fit model

The enzyme can change its shape

1. One substrate molecule binds weakly2. The enzyme’s active site changes shape so

that a second substrate molecule can bind3. The second substrate binds

Chemical process (rx) occurs

FACTORS AFFECTING ENZYME FACTORS AFFECTING ENZYME ACTIVITYACTIVITY

1. Temperature2. pH

TemperatureTemperature

Increase in activity with temperature (molecules have more energy)

... but only to a certain point.

Too much heat will disrupt the 2° , 3° and 4° structure◦Denaturation & loss of function

Every enzyme has a temperature at which it functions best – this is the optimal temperature

For human enzymes it is usually 37°C (body temp.)

pHpH

Enzymes also have optimal pHsThese will vary according to the location

in which they function

Location Optimal pH

Pepsin Stomach 2

Trypsin Small intestine 8

REGULATION OF ENZYME ACTIVITYREGULATION OF ENZYME ACTIVITY

1. Inhibition2. Allosterically3. Feedback inhibition

Competitive inhibitionCompetitive inhibitionAre very similar in shape to an enzyme’s

substrate.Bind to the active site, and physically

block the correct substrate from binding.

Competitive InhibitionCompetitive Inhibition

Enzyme Efficiency / Rate of RxEnzyme Efficiency / Rate of Rx

Noncompetitive inhibitionNoncompetitive inhibition

May be allostericOR

The inhibitor directly affects the enzyme so that it cannot carry out its function. (chemicals that alter the enzyme’s shape and therefore function)

Noncompetitive inhibitionNoncompetitive inhibition

Noncompetitive inhibitionNoncompetitive inhibition

Comparing the 2 inhibitionsComparing the 2 inhibitions

Allosteric RegulationAllosteric RegulationAllosteric site – Site on an enzyme that

can bind with an effector.NOT the same as active site.

Effector:◦Activator, or◦ Inhibitor

Inhibition vs ActivationInhibition vs ActivationInhibitors vs ActivatorsInhibitors vs ActivatorsSome substances can inhibit enzyme

function – Inhibitors Some substances can enhance enzyme

function – activators

Inhibition can be either competitive or noncompetitive

Allosteric activatorStabilize the active-form

Allosteric inhibitorStabilize the inactive form

See pg. 73, Figure 7

Feedback inhibitionFeedback inhibition

Feedback inhibition: The product of a series of enzyme-catalyzed reactions acts to allosterically inhibit an enzyme that acts earlier in the series.

Often biological reactions occur in a series.

WHY IS FEEDBACK INHIBITION WHY IS FEEDBACK INHIBITION important?important?5 minutes discussions:WHY DO CELLS NEED FEEDBACK?WHY DO YOU NEED FEEDBACK?“TWO-WAY” WORLD ANYONE?

SOME APPLICATIONSSOME APPLICATIONSCheese-makingCow enzyme rennet

Insulin for Type 1 diabetics

Lactase to digest lactose

There are three main enzymes There are three main enzymes found in a human body found in a human body

1. digestive enzymes2. metabolic enzymes3. food enzymes

Who’s ‘ase is it anyways?Who’s ‘ase is it anyways?Naming enzymes most end in “ase”