Enzyme Kinetics and Inhibition Flashcards
This parameter is the concentration of substrate at 1/2 the Vmax
Km
The higher the Km, the ______ the affinity
lower
True or False: You can change Vmax by changing substrate concentration
False
What is the Michaelis-Menten equation?
V=Vmax [S] / Km + [S]
What does the x intercept on a line-weaver burke plot tell you?
The X-intercept is = -1/Km
What does the y intercept on a line-weaver burke plot tell you?
The Y-intercept is = 1/Vmax
The following Lineweaver-Burk plot depicts an enzyme-catalyzed reaction (A) and the same reaction in the presence of an inhibitor of the enzyme (B). What kind of inhibition is it showing?
Uncompetetive. The inhibitor decreases Vmax and decreases Km.
What happens to Km if a mixed inhibitor binds preferrably to the enzyme and not the enzyme-substrate complex?
When it binds preferrably to the enzyme, it increases Km.
What kind of inhibition is shown in the following plot:
Competetive inhibition, Km is changed but Vmax is still the same.
What kind of inhibition is shown in the following plot. Note that the red line is the unihibited plot:
Noncompetetive. The X intercept is the same but the y intercept has changed meaning Km is unchanged but Vmax is decreased.
What kind of inhibition is shown in the following plot:
Competetive. Y intercept is unchanged meaning the vmax is unchanged. X intercept has increased in the presence of the inhibitor indicating a decrease in affinity for the substrate because it is competing.
What type of inhibition is exhibited in the graph below if you start with blue?
Since the x intercept is brought in, that means that Km is increased. Vmax is decreased since the y intercept moved up on the graph. Think:
Competetive: Vmax unchanged, Km increased
NonComp: Vmax decreased, Km unchaged
Uncompetetive: Vmax decreased, Km decreased
Mixed inhibition is the only inhibition that could show this kind of plot
Competetive inhibitors bind to the __________
active site
Noncompetetive inhibitors bind to the _____________
allosteric site
Uncompetetive inhibitors bind to the _____________
ES complex
Mixed inhibitors bind to the ____________
E or ES complex with different affinities
Mixed inhibitors always decrease _______ but they vary in how they change _______
always decrease Vmax, vary in how they change Km
When will a mixed inhibitor increase Km?
When the inhibitor binds to the free enzyme (similar to competetive inhibitor)
When will a mixed inhibitor decrease Km?
When it prefers to bind to the ES complex (so like an uncompetetive inhibitor)
The rate of the carbonic anhydrase-catalyzed reaction is extremely fast (≈ 10^6 reactions per second) and can be performed in the forward or reverse directions. According to this info, which of the following properties of carbonic anhydrase are represented by the value 10^6?
I. Turnover number
II. [ET]
III. Vmax
IV. kcat
I and IV only
In enzyme kinetics, turnover number (aka kcat) is defined as the maximum number of chemical conversions of substrate molecules per second that a single catalytic site will execute for a given enzyme concentration ([ET]). Turnover number can be calculated from the maximum reaction rate (Vmax) and enzyme concentration as follows (I and IV):
kcat = Vmax/[ET]
What is Kcat?
Kcat is the turnover rate
kcat = Vmax/[ET]
Which type of inhibitor does NOT alter the KM/Vmax ratio of an enzyme?
This Biochemistry question falls under the content category “Structure and function of proteins and their constituent amino acids.” The answer to this question is B because uncompetitive inhibitors do not alter the slope of the Lineweaver–Burk plot, which is equal KM/Vmax. It is a Scientific Reasoning and Problem Solving question because you must work with various models of enzyme inhibition to determine the correct answer.
An enzyme is more effectively inhibited by uncompetitive inhibitors when:
the substrate concentration is decreased.
the substrate concentration is increased.
the inhibitor concentration is increased.
the substrate concentration is increased.
the inhibitor concentration is increased.
What iscatalytic efficiency/
Kcat/Km
Ternary Complex
A ternary complex can be a complex formed between two substrate molecules and an enzyme. This is seen in multi-substrate enzyme-catalyzed reactions where two substrates and two products can be formed. The ternary complex is an intermediate between the product formation in this type of enzyme-catalyzed reactions.
Ping Pong Mechanism
Also known as a double displacement mechanism, this mechanism involves the binding of two substrates to an ezyme without forming a ternary complex (so no two substrates will bind at the same time)
Ordered Mechanism
There is a specific order that the substrates bind
Random Order Mechanism
Of two possible substrates, either can bind first
