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! kickstarting-chemical-reactions-vance-kite 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 efruit-juice-drug-interactions.html 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!