SFP6: Theory Of Enzyme Catalysis Flashcards
What is an enzyme?
A protein which catalyses biological reactions
What is a catalyst?
A substance that increases the rate of a reaction without being consumed in the reaction
What is the reaction rate equation?
Reaction rate = k[A]
Rate is dependent on concentration of reactants
What does [A]o stand for?
Initial concentration of A
What is reaction coordinate?
Depicts progress of reaction
What is the path called that the reactants approach one another along?
Path of minimum, free energy
At what value of deltaG is the reaction thermodynamically favourable?
< 0
What is the peak of a free energy diagram called?
The peak is called the transition state (TS)
Why do we need an enzyme if a reaction is thermodynamically favourable/spontaneous?
Spontaneous doesn’t necessarily mean fast
What is the difference in free energy between reactants and transition state known as?
The activation energy for the reaction.
Does a greater activation energy mean slower or faster reaction?
Slower reaction
K is directly proportional to deltaG (activation energy)… true or false?
False
K is directly proportional to 1/deltaG
K is directly proportional to [TS]… true or false
True
[TS] is directly proportional to delta G… true or false?
False, [TS] is directly proportional to 1/deltaG
What is eyring equation and what does it show?
K= ((Boltzmann constant X T) / h) exp (-delta G/ RT)
H=Plancks constant
R=gas constant
Shows that increased k decreases activation energy in a log effect (small decrease means big increase)
How does an enzyme reduce the activation energy?
By stabilising the transition state
What physically is a transition state?
A-B + C -> A + B-C
There must be a point at which A-B is being broken as B-C is being formed
Is A- - - B- - -C high or low energy?
High energy, it is very unstable
What is an example where transition state occurs?
Esters
They are broken down by lysozyme and must move through a very unstable state
What can activation energy be separated into?
Enthalpic and entropic terms (H and S)
DeltaG= DeltaH- TdeltaS
What are two catalytic mechanisms used by enzymes for changing deltaH?
1) general acid-base catalysis
2) electrostatic catalysis
What are two catalytic mechanisms used by enzymes for changing deltaS?
1) proximity and orientation effects
2) covalent catalysis
What is general acid-base catalysis (changing deltaH)?
Neutralise-stabilise energetically unfavourable charge formation
General acid catalysis- stabilises formation of developing -ve charge by H+ transfer from acid
General base catalysis - stabilises formation of developing +ve charge by H+ transfer to base
What is electrostatic catalysis (changing deltaH)?
Changes stabilised by electric field from charged side chains or metal ions from the enzymes
