Lecture 9 Flashcards
How do enzymes work as catalysts?
By providing an alternate path of lower activation energy
What is a progress curve?
A curve displaying the measures of the appearance of produce (or disappearance of substrate) with time
Where is velocity measured from on a progress curve?
From the linear proportion; initial velocity
Why can the parabolic portion of a progress curve not be used to measure velocity?
There are too many unknowns
What is the relationship between enzyme and velocity?
Linearly proportional
What are the effects of an infinite substrate concentration?
Increases in a linear way however as all active sites within the enzyme become occupied, the ROR stops increasing = Vmax
What order of reaction is the linear portion of the progress curve?
First order, rate is dependent upon substrate concentration
What order of reaction is the parabolic portion of the progress curve?
Zeroth order, rate is not dependent on substrate concentration
How can Vmax be increased?
By adding more enzyme and therefore more active sites
What is the Michaelis constant?
Km; the substrate concentration required to generate half the Vmax
What is the Michaelis-Menten equation?
V = Vmax [S] / Km + [S]
What are the simplifying assumptions of Michaelis-Menten model?
Product is not converted back to substrate, Haldane’s steady-state assumption, only measuring initial ROR means that [S] does not change over time ( [S] > [E] )
What is Haldane’s steady-state assumption?
The rate of ES complex formation is equal to the rate of its breakdown d[ES] / d t = 0
What is the Lineweaver-Burk plot
Plotting the inverse of the Michaelis parabolic plot to get a linear plot
What is the y-intercept of the Lineweaver-Burk plot?
1 / Vmax
What is the x-intercept of the Lineweaver-Burk plot?
-1 / Km
What is the slope of the Lineweaver-Burk plot?
Km / Vmax
What are the units of Km
Concentration so; mmol / L
What does a low Km relate to?
High affinity for bonding to that particular substrate
What does a high Km relate to?
Low affinity for bonding to that particular substrate
In a cell, what is the typical range of [S]?
Often around or below the Km value, meaning that rate control is effective and substrates aren’t queuing for active sites
What is Kcat?
Definition
The turnover number; the number of substrate molecules converted to product, per enzyme, per time
What conditions is Kcat measured under?
Enzyme is saturated with substrate
What is Kcat?
Measure of…
The catalytic activity of an individual enzyme molecule
