Review Enzymes are specific to a substrate

Based on shape (lock & key) Enzymes are NOT consumed or changed

by catalyzed reaction Great for speeding up reactions! Can be denatured…

Enzymes do not add energy They lower activation energy Results in higher reaction rate (faster)

Enzyme Regulation How cell affects enzyme activity (rate) “on

purpose” regulate activity Can send “signal molecule” binds

enzyme in 2 ways:

1) Can bind directly to active site:

prevents substrate bind only repress

2) Can bind “elsewhere” on enzyme to change enzyme shape (allow OR prevent

substrate binding): activate or repress

Allosteric enzymes: can change to other shape by signal

molecule

Allosteric site

Faster/slower?Enzyme on/off?

Enzyme Regulation Names If repressor signal molecule binds

to active site… Called competitive inhibition

If repressor signal molecule binds to allosteric site…

Enzyme changes shape Active site no longer fits Called noncompetitive

inhibition Not all enzymes have an allosteric site

Not all enzymes are allosteric…

http://www.northland.cc.mn.us/biology/biology1111/animations/enzyme.swf Enzyme Inhibitors

Allosteric Enzyme Regulation Repressor signal molecule

Will change shape so CANNOT bind Activator signal molecule

Will change shape so CAN bindActive Site Allosteric

Site

http://bcs.whfreeman.com/thelifewire/content/chp06/0602002.htmlhttp://course1.winona.edu/sberg/animtns/allostan.gif

Feedback Inhibition System of enzyme regulation where product

of reaction can be signal molecule (inhibition repressor) Competitive feedback inhibition

Product binds directly to active site

Noncompetitive feedback inhibition Product binds to allosteric site

Allows for self-regulation If too much product, stops catalysis (repress) If too little product, continues catalysis

Binding not permanent (can diffuse away)

Product

ProductProduct

Product

Product

Product

Product

Product

Product

Product Product

Product

Product

Product

(Biochemical) Metabolic Pathway A “chain” reaction

Involves several enzymes (closeby)

Product of one catalyzed reaction becomes substrate for next

Desired product only made at end of pathway Similar to Assembly Line

http://highered.mcgraw-hill.com/classware/ala.do?isbn=0072986670&alaid=ala_1048052&showSelfStudyTree=true

Allows for more precise control

http://www.northland.cc.mn.us/biology/biology1111/animations/enzyme.swf - Feedback Inhibition

http://highered.mcgraw-hill.com/classware/ala.do?isbn=0072986670&alaid=ala_1048055&showSelfStudyTree=true

Prepare for a mix/match of different regulations

Noncompetitive Inhibition = allosteric enzyme with repressor (simple)

Noncompetitive Feedback Inhibition = allosteric enzyme with product being repressor

Noncompetitive Feedback Inhibition of a Biochemical Pathway = several enzymes with at least 1st enzyme being allosteric and product of last enzyme being a repressor to 1st enzyme

Environmental Affects on Enzymes Increase amount of

substrate Increase amount of

enzyme Increase temperature Increase pH Increase an repressor

molecule Having a Feedback

Inhibition

Rat

e

SubstrateEnzymeTemperaturepHRepressorTimeSubstrate

Protein works slow

Protein works best

Protein denatures

Protein denatures

Protein works best

An Example

H2O2 = Hydrogen peroxide (reactant) Can spontaneously break down to

H2O water and O2 gas (products)…so this is an…

Exergonic reaction

2H2O2 2H2O + O2

Enzymes speed up this reaction by… lowering activation energy…how exactly?

In terms of motion of molecules, how is it lowered?

Energy Profile of Exergonic Rxn Note

release of energy

Note EA

Activation Energy Energy required to start reaction = The energy needed to get molecules into transition stateCan accomplish by moving faster (i.e. add heat: thermal energy)

Enzymes lower Activation Energy Release of energy same as without enzyme

Howenzymes

lower

activ.

nrg?(molecular

level)

Substrate-Specificity (by shape) Substrate = reactant(s) catalyzed by enzyme Substrate binds to enzyme on active site Forms enzyme-substrate complex (H-bonds)

Induced fit: enzyme changes shape SLIGHTLY to “cuddle” substrate

Active Site is shape-specific – catalyze on specific substrate

Induced fit lowers activation energy because orients substrate(s) correctly

Enzyme Catalysis

Enzyme does NOT change in catalysis (retains shape)Enzyme is ready to catalyze another substrate after

reaction is complete (after products released)

Note on Molecular Motion:It’s still all about “chance”

Substrates can hit enzyme in “wrong” way and not be catalyzed…

But since enzyme has active site (fitted shape), more likely to react than if substrate on own

Rate of Reaction

How quickly turn reactants into products NOT how much products are made

Rate of Catalysis = rate of enzymes How quickly do enzymes catalyze

Rate is affected by several environmental factors

Rate of Catalysis

Rate of Catalysis

Rate = 1 rxn in 1 secRate = 2 rxn in 1 sec

Rate of Catalysis

Rate = 10 rxn in 1 sec

Rate of Catalysis

Rate = 20 rxn in 2 sec = 10 rxn in 1 sec

Rate of Catalysis

As you increase substrate concentration, rate will increase until…

Enzymes are saturated and then rate will level off (enzyme still working…)

As you increase enzyme concentration,

rate will increase (indefinitely?)

Only when Enzymes >>>>> Substrate,

rate will level off eventuallySaturation more likely if increase substrate (not enzyme)

Rate of Catalysis

Rate = 20 rxn in 1 secRate = 20 rxn in 2 sec

Rate of Catalysis

Rate = 5 rxn in 1 secRate = 5 rxn in 0.9 sec

With more enzymes, there is a higher chance of substrate hitting correctly and reacting -- this increases rate

But at some point, rate will level off

Compared to increasing substrate, this level off will be (@ a much higher concentration of enzyme and @ a much higher rate)

Graphing Enzyme Rates

Increase amount of substrate

Increase amount of enzyme

Rat

e

Enzyme Substrate

2 more factors affecting enzyme rate Same 2 factors that cause denaturation…

TemperatureIncrease temp. will

move molecules faster

but…break H-bonds pH

Change in H+ concentration will

disrupt H-bonds + affect cross-linking

in enzyme:not functional

Environmental Affects on Enzymes Increase amount of

substrate Increase amount of

enzyme Increase temperature Increase pH Increase an repressor

molecule Having a Feedback

Inhibition

Rat

e

SubstrateEnzymeTemperaturepHRepressorTimeSubstrate

Protein works slow

Protein works best

Protein denatures

Protein denatures

Protein works best