Free Gibbs Energy: The portion of a system's energy That can perform work at constant temp and pressure Free Energy Change: G= G(final state)- G(initial state) G= H- TS H= change in Enthalpy (available energy) T=Temperature in Kelvin (C+ 273) S= change in entropy G is negative: Reaction is thermodynamically favorable Spontaneous Exergonic G is positive: Reaction is not favorable Non-Spontaneous Endergonic G=0: Reaction is at equilibrium
Example: Hydrolysis of Sucrose
Spontaneous but VERY slow (years!) Add Enzyme (Sucrase) speed up reaction (seconds!)
ENZYMES SPEED UP REACTIONS BY LOWERING ENERGY BARRIERS (EA)
EA : ACTIVATION ENERGY
MECHANISMS ENZYMES USE TO SPEED UP REACTIONS
1) BRING SUBSTRATES CLOSE TOGETHER
2) STRESS BONDS IN SUBSTRATE STABILIZE TRANSITION STATE INTERMEDIATE
3) PROVIDE A FAVORABLE ENVIRONMENT FOR REACTION TO OCCUR
4) DIRECT PARTICIPATION
ENZYMES ARE SUBSTRATE SPECIFIC
SUBSTRATE/REACTANT: what enzyme acts on can be > 1 substrate
ACTIVE SITE: Part of the enzyme that binds substrate Pocket formed by amino acid side chains
SPECIFICITY: fit between enzyme and substrate compatible only for that reaction
INDUCED FIT: substrate binds at active site conformational change occurs like a clasping handshake stretches bonds
ATP: Energy Currency of the Cell
Energy stored in phosphate bonds---Why???
ATP Hydrolysis: ATP+ H20 G= - 7.3 kcal/mol
ADP + Pi
HOW DOES ATP PERFORM WORK?:
WHAT CAN CELL A DO WITH ATP?
3 TYPES OF WORK 1) Mechanical
2) Transport
3) Chemical
REACTION RATES WITH AND WITHOUT AN ENZYME
Temp dependence of enzyme reactions
Enzyme regulation affects the reaction RATE 3 Types of Inhibitors 1. Competetive Inhibitor
A) B) C) D) Binds to Active Site of Enzyme Similar shape as substrate COMPETES with substrate for active site REVERSIBLE--inhibitor can fall out of active site -- by increasing concentration of substrate (outcompete inhibitor)
2. Irreversible inhibitor
A) B) C) D)
Binds to ACTIVE SITE Makes covalent bonds (IRREVERSIBLE) Enzyme Non-functional Removes Enzyme from reaction
2. Non-competetive inhibitor
A) Binds AWAY from active site (2nd site) B) Reversible C) Causes CONFORMATION CHANGE in the enzyme ACTIVE SITE INACCESSIBLE
An example of ALLOSTERIC REGULATION
ALLOSTERIC REGULATION
regulation that affects the conformation of the enzyme -both positive and negative regulation
-Any
ALLOSTERIC ACTIVATOR: + Regulation Activator binds away from active site Conformational change occurs Stabilizes active form of enzyme REVERSIBLE ALLOSTERIC INHIBITION: - Regulation Binds away from active site Conformational change occurs Stabilizes inactive form of enzyme REVERSIBLE
ALLOSTERIC REGULATION: COOPERATIVITY Ex: Hemoglobin
FEEDBACK INHIBITION
-Metabolic pathway is inhibited by its end product binds to an enzyme early in pathway Shuts off the system when enough end product