Enzymes Part 3 Chapter 3

Factors that Effect Rate of Enzyme Catalyzed Reaction Enzyme Concentration Substrate Concentration 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 of product will be the same What will change? Rate at which product is made…especially INITIAL RATE of RXN for each different trail Analyze rates of Rxns at beginning of each trial Calculate slope of curve at 30s for each trial (most realistic way) Plot second graph Enzyme concentrations vs. initial rates of rxn Analyze relation ship Predictions? Initial Rate of rxn increases with increasing concentration of enzyme More enzyme=more active sites available for substrates=more products being made per time

Substrate Concentration Keep enzyme concentration constant and change concentrations of substrate in each trial Curves all look similar Plot second graph showing initial reaction rates vs. substrate concentration Linear Flattens out at top (Vmax) Increase substrate concentration= increase in initial rate of rxn More substrate=more often enzyme’s active site can bind with substrate= increased INITIAL rate of rxn What happens if we keep increasing substrate concentration (keeping Enzyme concentration the same)? Enzymes are working as fast as possible Substrates are line up and wait for next available 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 ENERGETICALLY until the bonds giving the enzyme its specific shape begin to break (hydrogen bonds are the first to go)…this is called… DENATURATION When the enzyme begins to lose its shape and activity\often irreversible 1st: substrate does not fit as perfectly into active site (takes more time to get situated and make product…rxn slows down) 2nd: Substrate can’t fit in active site at all = NO PRODUCT being made reaction cannot occur (rate of rxn=0)

Temperature at which the enzyme catalyzes a reaction at the maximum rate Human body temperature 37*C Optimum temp. For human enzymes  40*C Different organisms have different optimum temperatures 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 and R-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  less substrate molecules being able to fit in active site  less products 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  substrate binds easily to active site, products continue being made More inhibitor than substrate  collisions between substrate become less likely  decrease in the amount of product being made  decrease in rate of reaction REVERSIBLE Increase conc. Of substrate Ex. Ethylene glycol (antifreeze) Enzyme in body converts ethylene glycol to oxalic acid = kidney damage Competitive inhibitor = Ethanol…fits active site It ethanol is increased, in will bind to active site of enzyme, preventing ethylene glycol from being converted into oxalic acid The rxn is slowed enough to allow the antifreeze to be excreted before kidneys are damaged Similar shape to substrate bind to active site, but do not make the intended product Relative concentrations of inhibitors effect the degree to which an inhibitor will slow down a 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 much substrate 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 effect…reaches active site changes active site shape substrate cannot fit active site no product 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 from overproducing 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 site of the first enzyme catalyzing the rxn  active site changes shape  no more substrates bind to enzyme  no more final product being made product levels decrease  product that is bound to enzyme 1 is released when product levels are low (in order to be used up for another chemical rxn)  enzyme 1’s active site regains its shape>substrate can now bind to active site  product concentration increase…and then we are back to the beginning

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 substrate molecules Enzyme is saturated with substrate Vmax is measured by calculating the steepest point of the curve Reaction rate is measured at different substrate concentrations (independent variable), while keeping enzyme constant As concentration of substrate is increased, reaction rate rises until it reaches it maximum rate (Vmax)