Download Enzymes

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Chapter 3
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* Enzyme Concentration
* Substrate
Concentration
* Temperature
* pH
* Inhibitors
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* 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
* 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)
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*
* 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
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*
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
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*
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)
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* 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)
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*
*
* 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
* 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
* 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
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* Inhibitor can bind briefly OR permanently
* Adding more substrate will not effect non-competitive inhibitors actions
* Different types
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*
*
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)
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*
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Do NOT have same shape as substrate
*
Ex. Digitalis (foxglove plant enzyme)
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
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*
Binds to ATPsynthase  heart muscle cannot pump out acetylcholine  increased contraction of heart muscle
IRREVERSIBLE or REVERSIBLE
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*
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
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* 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)