Incredible EnzymesMrs. 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 increasingHow 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 reactionMost 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-ki

ckstarting-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 siteEnzyme unable to bind with substrateSlows down or stops enzyme from acting since

some enzymes are inactivatedMany 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 InhibitorsInhibit 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 Inhibitorshttp://www.cbc.ca/news/health/story/2012/11/

26/grapefruit-juice-drug-interactions.html

Non-Competitive InhibitionMolecules 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 RegulationMolecules 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!