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… Enzyme Inhibitors

Allosteric Enzyme Regulation Repressor signal molecule Will change shape so CANNOT bind Activator signal molecule Will change shape so CAN bind Active Site Allosteric Site

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

(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 hill.com/classware/ala.do?isbn= &alaid=ala_ &showSelfStudyTree=true Allows for more precise control - Feedback Inhibition

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 1 st enzyme being allosteric and product of last enzyme being a repressor to 1 st 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 Rate SubstrateEnzymeTemperaturepHRepressorTimeSubstrate Protein works slow Protein works best Protein denatures Protein works best

An Example H 2 O 2 = Hydrogen peroxide (reactant) Can spontaneously break down to H 2 O water and O 2 gas (products)… so this is an… Exergonic reaction 2H 2 O 2  2H 2 O + O 2 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 E A Activation Energy Energy required to start reaction = The energy needed to get molecules into transition state Can accomplish by moving faster (i.e. add heat: thermal energy)

Enzymes lower Activation Energy Release of energy same as without enzyme How enzymes 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 = 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 eventually Saturation 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 a much higher rate)

Graphing Enzyme Rates Increase amount of substrate Increase amount of enzyme Rate EnzymeSubstrate

2 more factors affecting enzyme rate Same 2 factors that cause denaturation… Temperature Increase 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 Rate SubstrateEnzymeTemperaturepHRepressorTimeSubstrate Protein works slow Protein works best Protein denatures Protein works best