Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
12 Cards in this Set
- Front
- Back
True facts about enzymes
|
-rxns occur at the active site, usually a crevice on the surface of the enzyme
-substrate must bind to the enzyme before an rxn can occur -enzyme yields a specific produce, nonbiological catalyst may produce more than one product and side rxns may occur -generally, enzymes are specific for a substrate -most are proteins, exceptions are catalytic RNAs |
|
What do enzymes promote?
|
-formation of a transition site, lower activation energy, increase magnitude of the rate constant for both the forward and reverse rxns
-activation energy is the difference between the transition state and reactants |
|
Enzymes cannot change the value of
|
delta G,
|
|
Acid-base catalysis
|
-a proton is transferred between enzyme and substrate
-may use a.a. such as aspartate and lysine -lowers the energy or stabilizes the transition state or intermediate -catalyst retains its original for after rxn occurs |
|
Covalent catalysis
|
-temp. covalent bond forms btwn the nucleophile functional group of an enzyme and the substrate, yielding the intermediate
-two-part process involving the formation of the intermediate and the breakdown of the intermediate -lowers the energy or stabilizes the transition state or intermediate -catalyst retains its original for after rxn occurs |
|
Metal ion catalysis
|
-mediating oxidation-reduction rxns
-properly orienting the substrate in the enzyme active site through ionic interactions -stabilizing a negatively charged intermediate -lowers the energy or stabilizes the transition state or intermediate -catalyst retains its original for after rxn occurs |
|
Enzyme labeling can be used to map the structure of the active site of an enzyme using an affinity label, a molecule that is structurally similar to the substrate.
|
-labeling involves irreversible covalent modification of the enzyme as the analog binds to the active site
|
|
Enzyme cofactors
|
-needed for catalyzing oxidative-reductive rxns and some group-transfer rxns
-metal ions -coenzymes, small organic molecules >transiently associated coenzymes, NADH, FADH, serve as "co-substrates" >tightly associated prosthetic groups -apoenzyme (inactive) + cofactor = holoenzyme (active) |
|
Free energy of activation DGǂ
|
free energy of transition state - free energy of reactants
|
|
(kB * T/h) * e^(-deltaGǂ /RT)
|
kB = boltzman constant
h = planck's constant R = gas constant T = kelvin (273.15 + C) |
|
deltadeltaGcat=
|
deltaGǂuncat - deltaGǂcat
|
|
Rate enhancement (ratio of the rates of the catalyzed and uncatalyzed reactions) is given by
|
e^deltadeltaGcat/RT
|