1. Enzymes Part 3
Chapter 3

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

3. 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

4. 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

7. 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)

9. 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

10. 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

12. Non-competitive (Allosteric)
Enzyme Inhibitors

13. 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

16. 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

19. 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

21. 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)