Chapter 8 Notes Flashcards
Enzymes?
biological catalysts that speed up chemical reactions by several orders of magnitude
Enzymes affect __ not reaction equilibria.
reaction rates
Substrates?
reactants that bind enzymes
__ change the barrier and speed up the reaction.
Enzymes
Difference between delta-G and delta-G-prime?
delta-G: tells you if RxN will occur under these conditions
delta-G-prime: tells you under standard conditions if RxN goes to completion
How do you find delta-G?
=Delta-G-Prime + RT ln Keq
Keq (equilibrum constant) =
[products]/[reactants]
Delta-G-Prime =
-RT ln Keq
When RxNs will not proceed, what can you add to make them proceed?
more reactants or products
Enzyme kinetics vs. enzyme thermodynamics?
enzyme kinetics: relates to speed of RxNs
enzyme thermodynamics: tells you whether a reaction can occur
What two things cause activation energy (if in the right orientation) and what facilitates activation energy?
temperature and concentration
enzymes
How do enzymes stabilize the transition state?
by lowering the activation energy barrier through binding energy (this is how RxNs occur quickly)
Describe the lock and key model.
binding of substrate to enzyme happens at the active site; no enzyme-substrate change; substrate fits exactly into enzyme at active site; complimentary shape on enzyme
Describe the induced-fit model.
enzyme changes to fit substrate at active site; binding of substrate induces structure changes in the enzyme
Describe the conformational selection model.
selection for conformational substrates for function; pre-knowledge of dynamic properties can be used in drug design; substrate selects for conformation at the active site (fluctuating active sites); enzyme can go back to original state; RNA can act as a biological enzyme
How can the effect of enzymes on reaction rates be calculated?
by changing initial concentrations of substrates with time
What is the core of enzyme kinetics?
reactant is being consumed/product formed per unit of time
How do you measure RxN rates?
using initial velocity since reactants will have different values
What are the two assumptions of the Michaelis-Menten Equation?
1) formation of a specific ES complex is a necessary intermediate in catalysis 2) The ES complex eventually achieves a steady state
What is the Michaelis-Menten equation?
Vo = Vmax ([S] / (Km + [S]))
Forward rate vs. reverse rate?
forward rate: formation of ES complex
reverse rate: breakdown of ES complex
When is a double reciprocal (Lineweaver-Burk) plot used instead of a hyperbolic MM curve?
when extracting kinetic parameters
Difference between Lineweaver-Burk and MM?
Plot 1/Vo vs. 1/[S] in Lineweaver-Burk rather than Vmax vs. [S]
Which is preferred, MM or LB?
LB because it is harder to plot MM hyperbolic curves
Km =
Michaelis Constant = (K1 + K2) / K1
What does the Kcat/Km depend on?
pH, temperature, and certain conditions
In cells, __ value reflects the cellular concentration of substrates and is equal to the dissociation constant (Kd) of ES complex.
Km
Kcat?
catalytic turnover number; how much product an enzyme can form when at maximum efficiency
When Km is high = __ affinity for reactants.
low
When Km is low = __ affinity for reactants.
high
