Chapter 12 (Part 1) Flashcards
What does the rate constant k indicate?
The relative speed or efficiency of a reaction
Why do we usually focus on the enzyme kinetics at the beginning of a reaction?
The product formation over time during this period is mostly linear
Define a second order reaction.
The reaction rate is dependent on both the enzyme and substrate concentrations
Why do we simply second order reactions to pseudo first order conditions?
It is difficult to measure both enzyme and substrate concentration throughout the course of a second order reaction
How does one create a pseudo first order condition?
Add the substrate at such high concentrations that it is in great excess over the enzyme concentration. Basically, the concentration of enzyme will dictate the reaction rate.
When is the maximum enzyme reaction velocity (Vmax) reached?
When an enzyme is completely saturated with substrate
(T/F) Under steady state conditions, the rate of enzyme-substrate complex formation is not equal to the rate of enzyme-substrate complex decomposition
False. They are equal. The rate of ES formation is determined by multiplying K by the concentration of free enzyme and free substrate
The rate of ES decomposition is dependent on 2 factors. What are they? Describe them mathematically in terms of k and ES.
- If shifted back to E + S, rate=k-1 times the concentration of ES
- If shifted forward, rate=k2 times the concentration of ES
Why are Lineweaver-Burke plots useful?
They provide a way to estimate Vmax and KM by transforming the hyperbola defined by the Michaelis-Menten equation into a linear form
Why is the term “double-reciprocal” relevant to Lineweaver-Burke plots? Describe how one obtains Vmax and KM from a Lineweaver-Burke plot.
1/vo is plotted on the y-axis, and 1/[S] is plotted on the x-axis. The slope of the line is KM/Vmax, the y-intercept=1/Vmax, and the x-intercept= -1/KM
What is the meaning of the term KM?
Operationally defined as the substrate concentration where the enzyme is functioning at 1/2 of its maximum velocity
What is the relationship between KM and catalytic efficiency?
A greater KM value indicates a lower level of catalytic efficiency; a lower KM value indicates a higher level of catalytic efficiency
How do we use the dissociation constant (KD)? How do we calculate it?
Used to describe the binding affinity of an enzyme for its substrate. KD=k-1/k1
Why is KM a decent approximation for the affinity of an enzyme for its substrate?
Because KM=KD+k2/k1.
Actual KM values for enzymes are typically slightly above physiological substrate concentration conditions. What does this mean with regard to changes in substrate concentration?
It means that the enzyme rate is sensitive to changes in [S], and allows a cell to more easily control the flux through an enzyme reaction by controlling substrate availability
