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
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