Reactions

1. thermodynamically favorable (release free energy)
2. thermodynamically unfavorable (require free energy)

covalent bonds are stable so molecules don't react spontaneously at phys conditions
activation energy excites stable ground state > reactive transition states
activation energy (not thermodynamics) determine reaction rate
so exergonic reactions don't occur due to high activation energy without assistance

enzyme = act as catalysts, lower activation energy
unaltered at end of reaction
act only on substrates (unlike inorganic catalysts)
only speed up 1 reaction of substrate (of many potential ones)
specificty = 3D #3 and #4 structure
enzyme has active site where substrate binds (conformation change)

enzyme and substrate have weak ionic or H bond
break via thermal motion
enzyme active site = R groups (polar nonpolar electrically charged)
so nonpolar substrate can't bind to polar/charged active site
coenzymes may be required for binding (nonproteinaceous, unchanged)

enzyme stabilize transition state substrate molecule
(lowers activation energy)
don't change reaction equilibria
increase reaction rate by bonding multiple reactants simultaneoulsy

enzymes are controlled
temperature, pH, substrate [], and
chemical agents:
1.competitive inhibitor -compete for enzyme active site, overcome by [substrate]
2.noncompetitive inhibitors - change enzyme not at active site
3.irreversible inhibitors - bond enzyme active site permanently

allosteric enzymes have active/inactive states
negative modulators stabilize inactive state

cooperativity - enzyme with 2+ identical binding sites where one bind increases 2nd site bind affinity