Download Incredible Enzymes - Mrs. Tuma`s Biology Page

Mrs. Tuma
SBI 4UI
Thermodynamics:
 First Law of Thermodynamics:
 The total amount of energy in the universe is
constant, although the energy may change form
(e.g.: heat, light, kinetic energy)
Thermodynamics:
 Second Law of Thermodynamics:
 Disorder (entropy) in the universe is always
increasing
 Energy is transferred into less useable forms
over time!
The Paradox:
 Biological systems “appear” organized, but
entropy is always increasing
 How does anything get done?
Enter Enzymes!
 What is an enzyme?

A biological protein catalyst which reduces the
activation energy required for a reaction to occur
 What is activation energy?


The amount of energy required to start a reaction
Most biological reactions would not happen
spontaneously without a reduction in activation
energy
Energy and Biological Reactions:
Check it out!
 http://ed.ted.com/lessons/activation-energy-
kickstarting-chemical-reactions-vance-kite
The Theory:
Lock and Key Theory:
 One enzyme (the lock) has a specific shape for one set
of substrates (the key) and is very rigid
Is “Lock and Key” Theory the best
fit?
The Theory:
 Induced-Fit Theory
 Good evidence that shape of the active site changes
somewhat after substrate(s) bind to it
 Enzyme’s active site is still very specific to the substrate
but it is not so rigid
Controlling by Competitive Inhibition:
 Competitive Inhibition:
 A “look-alike” molecule binds to the active site
 Enzyme unable to bind with substrate
 Slows down or stops enzyme from acting since some
enzymes are inactivated
 Many common drugs and pesticides work this way!
Competitive Inhibition
Common Competitive Inhibitors:
 Penicillin
 kills susceptible bacteria by specifically inhibiting
the enzyme that catalyzes the final step in cell wall
biosynthesis
 ACE Inhibitors
 Inhibit enzyme that make angiotensin II hormone
(it constricts blood vessels, narrowing them and
increasing blood pressure)
 Commonly used to treat high blood pressure
More Interesting Competitive
Inhibitors…
 Ethanol
 Given as an antidote in methanol poisoning as it competes
for the same metabolizing enzyme but produces less toxic
effects
 Grapefruit!!!
 Compound(s) in grapefruit juice inhibit a drug-
metabolizing enzyme in the small intestine, allowing for
increased levels of the drug in the body
 Drugs can build up to toxic levels!
Common Competitive
Inhibitors
 http://www.cbc.ca/news/health/story/2012/11/26/grap
efruit-juice-drug-interactions.html
Non-Competitive Inhibition
 Molecules can bind to a site adjacent to the active site
and change the shape of the active site
 Substrate may then be unable to bind to the active site
 Eg: Heavy Metals
Allosteric Regulation
 Molecules may bind to a site away from the active site
and either increase enzyme action (allosteric
activation) or decrease enzyme action (allosteric
deactivation)
Common Allosteric Regulators:
 Many vitamins act as allosteric regulators
co-enzyme: vitamin aiding an enzyme’s action
co-factor: a mineral aiding an enzyme’s action
The End!