10: thermodynamics, atp hydrolysis, enzyme kinetics

thermodynamics

\-tells us whether a reaction will go or in what direction

if delta g for a → b is 10 kj/mole then

\-delta g for b → a is -10 kj/mole

delta h is neg

\-relief of electrostatic repulsion

\-initial p is stabilized by resonance

\-mass action favors hydrolysis (hydration of phosphate ion)

delta s is pos

\-more than one product is produced

when atp is hydrolyzed w h2o there are 220,000 molecules of adp +pi +h+ and only 1 molecule of atp at equilibrium, why?

\-the bind between the beta and gamma phosphates of atp is a phosphoanhydride bond that is unstable at ph 7.4 because of the large neg charge on the phosphate groups

\-this causes considerable electro repulsion of these groups. with hydrolysis of the gamma phosphate group, neg charges are removed and the electro repulsion relieved

\-bond energy is decreased (delta h = - )

When ATP is hydrolyzed with H2O, the reaction proceeds far to the right; at \n equilibrium (when the rx has stopped because rate of the forward and back rx are =) there are \n 220,000 molecules of ADP + Pi + H+ and ONLY 1 molecule of ATP left!! WHY?

\-atp (the one starting material) has become 3 products

* adp, inorganic phosphate, and H+ ions

\-increased number of products means entropy has increased

high energy bonds

\-have large neg standard G when hydrolyzed

\-is readily hydrolyzed and releases a large amount of nrg

\-yields products far in excess of the reactant at equilibrium

atp

\-2 phosphoanhydide bonds that are high nrg and have high phosphoryl group transfer potential upon hydrolysis with h2o

\-1 phosphodiester bond w lower nrg and lower phosphoryl group transfer potential upon hydrolysis w h2o

kinetics

\-how fast a reaction will go

side reactions

\-organic chemistry relies on collisions of molecules to overcome the activation energy

\-slow process

\-side reactions occur when the wrong collision orientation results in an or undesired side product

\-rate of collisions can be increased by increased temp or concentration of reactants

enzyme catalysis

\-active sites are complementary to the transition state

\-enzymes stabilize the transition state of the rxn

\-enzyme substrate complex formation uses non covalent bonds and yields a binding nrg to lower activation energies

sequence of enzyme catalysis

1. substrate binding
2. activation of substrate
3. product formation
4. enzyme dissociation


1. enzyme can now bind to other molecule for new round of rxns

substrate

\-molecule that binds w in an enzymes interior and there is a transformed product

active site

\-a cleft w in the enzyme where substrates bind

\-the small portion of the enzyme where the substrate becomes bound by noncovalent forces

Vmax

\-the maximal velocity that can be achieved w a given total enzyme concentration

\-can be measured at the limiting (max) velocity obtained for a fixed enzyme at saturating substrate

\-is proportional to the enzyme concentration and is a measure of how fast the rxn is catalyzed by the enzyme can proceed once ES is formed