Kinetics of enzyme reactions Flashcards
what is kinetics
study of the rate at which compounds react
the rate of an enzymatic reaction is affected by what 5 things
enzyme, substrate, effectors, temperature, pH
What is the unit for the rate of change in concentration
Moles/L Sec-1
Write out the Rate equation and explain what each thing
picture
Describe the relationship between the reactant and time for first order reactions
The amount of reactant decays exponentially
The slope for first order reactions for graph ln vs time is what?
How can you tell when a reaction is first order?
-k
Rate depends on the first power of the concentration
What is the equilibrium constant
Ratio of forward and reverse rate constants
Most biochemical reactions are what order
second order
what is the unit for second order reactions
(Mol/L)-1 s-1
Rate equations for second order
V= K2[A]^2 V= K2[A][B]
What allows enzymes to find their substrates
Thermal motion
How is initial velocity determined?
Bymeasuringproductformationasafunctionoftime velocity of reaction),andthendetermining thevelocitysoonafterthereactionhasstarted
What apparatus is used to measure initial velocity
Stopped flow apparatus
what is the michaelis menten equation?
V0= Vmax[S]/Km+[S]
What did Michaelis and Menten speculate about the enzyme, substrate and rate determining step? And show this in simple form
Substrate forms to an enzyme to make a complex in a fast and reversible step.
This complex then breaks down in a slower step to yield the free enzyme and product so is the rate limiting step.
E+S ES-> E + P
Assumptions made in deriving the M&M equation about k-2
k-2 = 0, so reverse reaction between P and E is negligible
why is the overall rate proportional to the concentration of Enzyme Substrate
The slower second reaction limits the overall rate
When [S] is small most of enzyme is in what form and so the rate is proportional to what?
Is in uncombined form and the rate is proportional to [S] (pseudo first order)
The maximum initial rate is observed when? (assumptions made in deriving MM equation)
when all the E is in the ES complex at high [S] i.e.
E is saturated (zero order)
when there is excess substrate the reaction quickly achieves what state
Steady state in which enzyme substrate remains approximately constant over time
How else V0 can be written
= v = Kcat [Etot][S]/ Km + [S]
What is Kcat the same as
K2
What is Kcat
turnover number
The number of substrate molecules one enzyme molecule can convert per second
Km is what
Michaelis constant
Approx measure of substrates affinity for an enzyme and the substrate conc which gives half maximal velocity (Vmax)
At high [S], velocity doesnt depend on what (Saturation Kinetics)
[S]
When Vo = 0.5Vmax, what is [S]
Km, Km is the substrate concentration that yields .5Vmax
The ideal rate is the M&M equation but deviations from this equation is due to what 4 things
- Limitation of measurements
- Substrate inhibition
- Substrate prep contains inhibitors
- Enzyme prep contains inhibitors
What is Km in terms of velocity
Conc of substrate giving half-maximal velocity
What is defined as the dissociation constant Kd of the ES complex or affinity of the enzyme for its substrate
When k2 is rate limiting k2
What is Km in terms of K-1, k2 and K1
(K-1+K2)/K1
Turnover number Kcat has units of sec-1, describe what is shows
Number of substrate molecules turned over per enzyme molecule per second
k1 (first order) has what unit and what does a large k1 mean?
K1 is the rate constant unit s-1
Large K1 means a fast reaction
Define Vmax Km V0 and which two contribute to measuring enzyme perfomance?
Vmax is maximumm velocity
Km is the substrate concentration at which V0 is equal to one half of Vmax
V0 is the initial velocity
Vmax and Km measure enzyme performance
How is Catalytic/Enzyme efficiency calculated? And what value must the result be in for it to be efficient?
Kcat/ Km
DeterminedbythefrequencywithwhichSandEcollide
108‐109M‐1s‐1 (The diffusion-controlled limit)
