enzymes part 3 chapter 3

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Factors that Effect Rate of Enzyme Catalyzed Reaction Enzyme Concentration Substrate Concentration Temperature pH Inhibitors


Enzymes Part 3 Chapter 3 Factors that Effect Rate of Enzyme Catalyzed Reaction
Enzyme Concentration SubstrateConcentration Temperature pH Inhibitors Enzyme Concentration Shape of curves will be the same Steep at beginning and gradually flatten out (level off) Amount of substrate remains constant in all trials Change concentration (amount) of enzyme in each trial Same concentration of substrate means concentration ofproduct will be the same What will change? Rate at which product ismadeespecially INITIALRATE of RXN for eachdifferent trail Analyze rates of Rxns atbeginning of each trial Calculate slope of curve at30s for each trial (mostrealistic way) Plot second graph Enzyme concentrations vs.initial rates of rxn Analyze relation ship Predictions? Initial Rate of rxn increaseswith increasingconcentration of enzyme More enzyme=more activesites available forsubstrates=more productsbeing made per time Substrate Concentration
Keep enzyme concentrationconstant and changeconcentrations of substrate in eachtrial Curves all look similar Plot second graph showing initialreaction rates vs. substrateconcentration Linear Flattens out at top (Vmax) Increase substrate concentration= increasein initial rate of rxn More substrate=more often enzymesactive site can bind with substrate=increased INITIAL rate of rxn What happens if we keep increasingsubstrate concentration (keeping Enzymeconcentration the same)? Enzymes are working as fast as possible Substrates are line up and wait for nextavailable enzyme Maximum rate for enzymes Known as Vmax (V=velocity) Substrate Concentration Temperature and Enzyme Activity
Low temperatures Rxn is slow Molecules moving slow Substrate molecules do not often collide with active site Bonding b/t enzyme & substrate is rare Takes a longer time to increase the concentration of products Temperature rises (higher) Substrate and enzyme molecules move faster Collisions more frequent Substrate enters active site more frequently and binds to active site more often Concentration of productions rapidly increase Extremely high temperature Molecules moving super fast Molecules in the enzyme begin vibrating VERY ENERGETICALLYuntil the bonds giving theenzyme its specific shape begin tobreak (hydrogen bonds are the first to go)this iscalled DENATURATION When the enzyme begins tolose its shape and activity\often irreversible 1st: substrate does not fit as perfectly into active site (takes more time to get situated and make productrxn slows down) 2nd: Substrate cant fit in active site at all = NO PRODUCT being made reaction cannotoccur (rate of rxn=0) Temperature at which theenzyme catalyzes areaction at the maximumrate
Human body temperature37*C Optimum temp. For humanenzymes 40*C Different organisms havedifferent optimumtemperatures Bacteria in hot springs Plants in cold environments(Boreal forest & Tundra) Optimum Temperature pH and enzyme activity What does pH measure?
How do H+ ions behave chemically? Increase concentration of H+ ions =increase chemical rxns between ions andR-groups of amino acids in enzyme =shape changing! AKA DENATURATION When H+ ions interact with R-group,ionization of R-groups can occur active site changes shape lesssubstrate molecules being able to fit inactive site lessproducts being made rate of reaction decreases Optimum pH for most enzymes= 7 neutral Exception: Enzymes in stomach (pepsin) pH and enzyme activity Non-competitive (Allosteric)
Enzyme Inhibitors Competitive Inhibitors
More substrate than inhibitor substratebinds easily to active site, products continuebeing made More inhibitor than substrate collisionsbetween substrate become less likely decrease in the amount of product beingmade decrease in rate of reaction REVERSIBLE Increase conc. Of substrate Ex. Ethylene glycol (antifreeze) Enzyme in body converts ethylene glycol tooxalic acid = kidney damage Competitive inhibitor = Ethanolfits active site It ethanol is increased, in will bind to active siteof enzyme, preventing ethylene glycol frombeing converted into oxalic acid The rxn is slowed enough to allow the antifreezeto be excreted before kidneys are damaged Similar shape tosubstrate bind to active site, but do notmake the intended product Relative concentrationsof inhibitors effect thedegree to which aninhibitor will slow downa rxn Non-competitive inhibitors
Inhibitor can bind briefly OR permanently Adding more substrate will not effect non-competitive inhibitors actions Different types react with active site portions of the active site completely different parts of the enzyme changing enzyme shape Inhibitor that permanently binds to active site no competition (no matter how muchsubstrate is added, you cannot change the fact that rxn will NOT occur) IRREVERSIBLE Ex. Penicillin blocks active site on bacterial enzyme that makes cell walls Attach to regulatory site (not active site) and change the shape of the entire enzyme(specifically the active site) Do NOT have same shape as substrate Disrupts hydrogen bonds and hydrophobic interactions that give enzyme specific 3D shape Domino effectreaches active site changes active site shape substrate cannot fit active site noproduct can be made reaction stops Ex. Digitalis (foxglove plant enzyme) Binds to ATPsynthase heart muscle cannot pump out acetylcholine increased contraction of heart muscle IRREVERSIBLE or REVERSIBLE Inhibitor binds permanently to regulatory site IRREVERSIBLE Inhibitor binds briefly to regulatory site REVERSIBLE Sometimes lethal but sometimes essential
Metabolic rxns controlled by inhibition to prevent enzymes fromoverproducing products (what could this do to the concentration of cellular fluid, blood, etc???) FEEDBACK MECHANISM (positive and negative) End-Product Inhibition Non-competitive inhibition Enzymes control every step of a multistep rxn The final product is a non-competitve inhibitor that binds to a regulatory siteof the first enzyme catalyzing the rxn active site changes shape nomore substrates bind to enzyme no more final product being madeproduct levels decrease product that is bound to enzyme 1 is releasedwhen product levels are low (in order to be used up for another chemicalrxn) enzyme 1s active site regains its shape>substrate can now bind toactive site product concentration increaseand then we are back to thebeginning Vmax Helps us understand how well an enzyme is functioning
Vmax is the maximum velocity of the reaction catalyzed Usually the initial rate of the reaction Always fastest at the beginning At Vmax all enzyme molecules are bound to substratemolecules Enzyme is saturated with substrate Vmax is measured by calculating the steepest point of thecurve Reaction rate is measured at different substrateconcentrations (independent variable), while keeping enzymeconstant As concentration of substrate is increased, reaction rate risesuntil it reaches it maximum rate (Vmax)


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