Biochem Enzymes Lecture 2 Flashcards
We study enzyme catalyzed reactions though _______
Enzyme Kinetics
In enzyme kinetics, we want to determine how ______ changes in response to experimental variables
Reaction rate
Substrate Concentration is important to rate determination, but [S] changes during the reaction as it is converted to product. We can simplify the problem by measuring the _____
Initial rate (initial velocity Vo)
What is the relationship of [S] and [E] at the start of a reaction?
So the [S] is thought of as
[S]»[E]
Constant
Vo (initial rate) can be investigated as a function of ___, which is varied by the experimenter
[S]
At low [S], Vo increases/decreases in an ~approximately linear fashion with an increase in [S].
Increases
At a higher [S], Vo increases become SMALLER/LARGER
Smaller until a plateau is reached
This is close to Vmax on the substate concentration and initial velocity curve
Plateau region
From the kinetic behavior in the graph figure, a theory was proposed
In a fast first step, the enzyme combines with its substrate to form….
In slower second step, the ES complex does what?
An enzyme substrate complex
Breaks down to give free enzyme and reaction product P
The slower reaction step that limits the overall reaction rate is called the….
Therefore, the overall rate must be proportional to the concentration of species that reacts in which step?
Rate Limiting Step
The slower second step
At low [S], the reaction rate is proportional to
[S] because the equilibrium favors formation
of ES as [S] increases
!
Vmax is reached when virtually all of the
enzyme is present as the…..
ES complex (no free enzyme)
When all of the enzyme is present as the ES complex, we can say that the enzyme is _____ with substrate. It is responsible for the plateau in the Vo vs. [S] curve
Saturated
The graph is an example of ___ kinetics. After the ES complex breaks down to P, the free enzyme can catalyze another reactant molecule
Note the a ____ state, microseconds long, occurs where ES initially builds up. The reaction quickly achieves a ___ state, where the [ES] is approximately constant
Saturation Kinetics
Pre-steady state
Steady State
E+S —> ES—-> E+P
Important equations
The measured Vo reflects the ______ state.
Analysis of initial rates are _______
Steady State
Steady state kinetics
The curve in fig. 6-11 can be expressed algebraically by which equation?
Michaelis-Menten Equation
What is the Michaelis Menten equation?
Vo = Vmax[S]/(Km + [S])
All of the terms in the Michaelis-Menten equation can be measured experimentally
!
Early in the reaction, the concentration of what is negligible?
P, so P—->S can be ignored
Vo is determined by the breakdown of ___ to ____
Therefore, Vo=?
[ES] to [P]
Vo = k2[ES]
Since the concentration of ES is not measured easily, the Vo = k2[ES] equation must be expressed differently
We begin by finding what?
The concentration of the enzyme
[total enzyme]
How is the total enzyme concentration expressed?
Therefore, how do you solve for free Enzyme?
Also, [S]» [Et], so the amount of substrate
bound by ES is negligible compared to [S]
[Et] = [E] + [ES]
[E] = [Et] –[ES]
!
In step 1, what is the rate of ES formation?
What is the rate of ES breakdown?
=k1([Et] – [ES])[S]
=k-1[ES] + k2[ES]
