Lecture 10 Flashcards
(14 cards)
What is the relationship between enzyme concentration [E] and reaction rate v ?
Reaction rate increases linearly with enzyme concentration. If [E] doubles, v also doubles.
What is the relationship between substrate concentration [S] and reaction rate v ?
Reaction rate depends on [S] in a hyperbolic fashion, described by the Michaelis-Menten equation.
How does an enzyme-catalyzed reaction transition from first-order to zero-order kinetics?
At low [S]: First-order kinetics (v proportional to [S])
At high [S]: Zero-order kinetics (reaction saturates at V max ).
What is the Michaelis-Menten equation?
v = (Vmax)([S])/ Km + [S]
v = initial reaction rate
V max = maximum reaction rate
Km = Michaelis constant (substrate concentration when v = 1/2 Vmax)
What does Km represent in enzyme kinetics?
The substrate concentration at which the reaction rate is half of V max. It reflects enzyme affinity for the substrate.
Low Km → high affinity (enzyme binds substrate tightly)
High Km → low affinity (enzyme binds substrate weakly)
What is vmax?
The maximum reaction rate when all enzyme active sites are saturated with substrate.
Why is the steady-state assumption made in Michaelis-Menten kinetics?
It assumes that the concentration of the enzyme-substrate complex ([ES]) remains constant during the reaction.
What is the definition of kcat (turnover number)? Also say example values.
The number of substrate molecules converted to product per enzyme per second when the enzyme is fully saturated with substrate.
kcat = Vmax / [E]total
Example values:
Catalase: kcat = 40,000,000 sec-1
Chymotrypsin: kcat = 100 sec-1
Lysozyme: kcat = 0.5 sec-1
What is enzyme efficiency and how is it measured?
Catalytic efficiency is measured using kcat/Km :
Higher kcat/Km = more efficient enzyme
Diffusion limit (~ 10^9 M-1sec-1) represents “perfect” enzyme efficiency.
What does a low Km value indicate about enzyme efficiency?
The enzyme reaches half of Vmax at a lower substrate concentration, meaning higher substrate affinity and potentially higher efficiency
What is the significance of a Lineweaver-Burk plot?
It linearizes the Michaelis-Menten equation by taking the reciprocal:
1/v = (Km/Vmax [S]) + (1/Vmax)
Slope = Km / Vmax
Y-intercept = 1/Vmax
X-intercept = -1/Km
What is the difference between a Michaelis-Menten plot and a Lineweaver-Burk plot?
Michaelis-Menten plot: A hyperbolic curve showing how v depends on [S].
Lineweaver-Burk plot: A straight-line version used for precise determination of Km and Vmax
How can enzyme efficiency (kcat/Km) be used in research?
To compare different substrates for the same enzyme.
To assess how mutations affect enzyme activity.
Why is kcat/Km considered a “specificity constant”?
It reflects both enzyme speed (kcat) and binding affinity ( Km ), making it the best measure of overall enzyme efficiency.
