Enzyme Kinetics Flashcards
How do enzymes speed up reactions?
They reduce the activation energy and bind to unstable transition states.
Formula for deltaG of a reaction A B [at equilibrium]
deltaG = deltaG(naught) + RTlnK(eq) where K(eq) = [B]/[A]
True or False: Catalysts change K(eq) of a reaction.
False: They increase K1 and K2 to the same degree, so K(eq) doesn’t change.
How to calculate the initial rate (Vo) of a reaction?
Vo = [deltaA]/t = -[deltaB]/t = K[A]^x
where x = reaction order
What does it mean for a reaction to be 1st order? 2nd order? Pseudo-first order? Zero order?
A reaction is first order if rate depends on first power of concentration of a single reactant, and second order if it depends on first power of concentration of two reactants.
1st order: A -> B; v = K[A]^1
2nd order: A + B -> C; v = K[A]^1[B]^1
Pseudo-1st order: A + H2O -> C; v = K[A]^1[H2O]^1
Zero order: A -> B; v = K[A]^0 where reaction rate won’t change with addition of A
Rate vs substrate concentration graph for first and zero order reactions?
Zero order: line with slope = O
First order: Diagonal line with positive slope
What happens to the reaction rate if the reaction S -> P occurs in presence of an enzyme?
Rate switches from first order [positive slope] to zero order [zero slope] as substrate concentration increases.
Michaelis-Menten base equation and derived equations?
E + S (K1)(K-1) ES ->(K2) E + P –K-2 assumed to be zero
Rate = K2[ES] d[ES]/dt = K1[E][S]
What is Kcat? How do you calculate it?
It is a measure of how many substrates an enzyme can convert into product per second. Formula:
kcat = Vmax/[E0] = K2
What is a Lineweaver-Burk plot? What do the X and Y intercepts signify? How can you calculate Kcat using this plot?
Linearized Michaelis-Menten curve where:
Y-intercept = 1/Vmax
X-intercept = -1/Km
You can use the y-int value to calculate Vmax, which can be used to calculate Kcat.
Reversible vs Irreversible enzyme inhibition? For which can you use MM curves/principles?
Reversible–enzyme remains intact, can be turned off by adding substrate or removing inhibitor
Irreversible–binds to and inactivates enzyme, effectively reducing amount of enzyme, CANNOT USE MICHAELIS-MENTEN HERE.
What are the features of a competitive inhibitor vs noncompetitive inhibitor structure?
Competitive inhibitors are often structural analogs to substrates, while noncompetitive inhibitors do not resemble substrates as they bind away from active sites.
How do competitive inhibitors affect Km and Vmax? How do noncompetitive inhibitors affect Km and Vmax?
How do uncompetitive inhibitors affect Km and Vmax?
Competitive- increases Km, no effects on Vmax
Noncompetitive- No effects on Km, decreases Vmax
Uncompetitive- Increases Km and decreases Vmax
