Enzymes Flashcards
Enzymes are…
biological catalysts that are unchanged by the reaction they catalyze
Enzymes act by…
stabilizing the transition state
Enzymes have…
an active site (site of catalyst)
Exergonic reactions…
release energy; delta G is -
Enzymes do not…
alter the free energy (delta G) or enthalpy (delta H)
Lock and Key Theory
the enzyme and substrate are complementary
Induced Fit Model
the enzyme and substrate undergo conformational changes to interact fully
Some enzymes require…
metal cation cofactors or small organic coenzymes to be active
The large rate accelerations of enzymes…
correspond to large decreases in the free energy of activation for the reaction
All reactions…
pass through a transition state on the reaction pathway
The active sites of enzymes…
bind the transition state of the reaction more tightly than the substrate
The catalytic role of an enzyme…
is to reduce the energy barrier between substrate (S) and transition state (X)
Rate acceleration by an enzyme means…
that the energy barrier between ES and EX must be smaller than the barrier between S and X
Enzyme catalyzes reactions by…
lowering the activation energy
For a given energy of EX, raising the energy of ES will…
increase the catalyzed rate
Raising energy will be accomplished by
loss of entropy due to formation of ES
destabilization of ES
Destabilization of ES by…
strain, distortion, desolvation
How does destabilization of ES affect enzyme catalysis
catalysis does not occur if ES and X are equally stabilized; catalysis will occur if X is stabilized more than ES
Formation of the ES complex results in…
entropy loss
Substrates typically lose waters of hydration in the formation of…
the ES complex
Electrostatic destabilization of a substrate…
may arise from juxtaposition of like charges in the active site
How tightly do transition-state analogs bind to the active site?
very tight binding (10^-20 to 10^-26)
Enzymes are often targets for…
drugs and other beneficial agents
Transition state analogs often make…
ideal enzyme inhibitors
