Objec&ve2.14b–Enzymes

•  Demonstratefactorsthataffectenzymeac&vity,includingdenatura&on,andinterpretgraphsshowingtheeffectsofvariousfactorsontherateofenzyme‐catalyzedreac&ons.

EnzymesandSpecificity

•  Themajorityofthegenomeencodesenzymes•  Eachenzymecanonlycatalyzeaspecificreac&on– Ac&vesitewillonlyaccommodateapar&cularsubstrate(reactant)

– Helpslimitthe“randomness”reac&ons– 3‐dimensionalshapecodedbythesequenceofaminoacids(codedbyDNAsequence)

•  Thousandsofmetabolicreac&onswithinanorganism…thousandsofuniqueenzymes

•  Enzymecatalysislowersac&va&onenergybyelimina&ngtherandomnessofreactantcollisions

•  Arrivalofthesubstrate(reactant)intheac&vesiteiss&llrandom

•  Increaseprobabilityofsubstrateenteringtheac&vesitebyincreasingsubstrateconcentra&on– Uptoenzymesatura&on

EnzymeAc&vityandSubstrateConcentra&on

Enzyme&ProteinShape•  Enzymeac&vityisdependentontheavailabilityoftheac&ve

site

•  Proteinisfoldedintoaspecificshapeasitissynthesized•  Proteinprimarystructureheldtogetherbynonpolarcovalent

bond(pep&debond…verystrong)

•  Secondary,ter&aryandquaternarystructureheldtogetherbyweakerhydrogenbonds,hydrophobicinterac&onsandionicbonds

HighTemperature,proteindenatura&on

•  Atomsandmoleculesareconstantlyinmo&on.•  Thehigherthetemperature,themorethemovementorvibra&on

•  Themoremovement/vibra&on,thelessstablethechemicalbondsthatholdtogetherthemolecule

•  Hightemperaturecanbreakbonds–especiallyhydrogenbonds

•  Theenzymeunfolds

LowTemperature,lessreac&oncollision•  Atlowertemperatures,moleculesmovemoreslowly

•  Lessvibra&on=morestablebondswithintheenzyme,nodenatura&on

But…•  Substrateslesslikelytocollide

•  Reac&onslesslikelytooccur

pH,ionsandProteinShape•  Secondary,ter&ary&quaternaryproteinstructurecanbedisruptedbychangesinpH

•  pHisameasureofH+concentra&on

•  H+isanionthatcancompeteforbindingtopar&cleswithnega&vechargesandthusbreakbonds

•  EachproteinhasanidealpHthatmaintainstherightshape

•  Sameeffectbyionsorsalts