Enzyme Kinetics Flashcards
What is the half-life of a reaction?
The time taken for half of the reactant, which is initially present, to be used up.
How can you determine whether or not a reaction is second order?
Plot 1/[S] against time- if the plot is a straight line, it is second order.
How can you determine whether or not a reaction is first order?
Plot ln[S] against time- if the plot is a straight line, it is first order.
How can rate laws be determined experimentally?
- absorption measurements, using a spectrophotometer.
- conductivity measurements, using a reaction between ions in solution.
- polarity measurements, for reactants and products that are optically active.
- using an aliquot method, by titrations.
What does the collision theory state?
A bimolecular reaction occurs when two properly orientated reactant molecules come together in a sufficiently energetic collision.
What is the relationship between kinetic energy and absolute temperature?
The average kinetic energy of a collection of molecules is proportional to the absolute temperature.
Describe an Arrhenius plot.
lnK against 1/T gives gradient -Ea/R and y intercept lnA.
What is the steady state assumption in the Michaelis-Menten equation?
The rate of ES production is equal to the overall rate of all the reactions that decrease [ES].
What is the Km?
The substrate concentration at which the reaction rate is half the maximal rate (Vmax).
What does it mean if an enzyme has a low Km?
It achieves maximal catalytic efficiency at low [S].
What is Kcat?
The turnover number- the number of reaction processes that each active site catalyses per unit time.
What are the disadvantages of the Lineweaver-Burk plot?
Most measurements of [S] are at high values, and the 1/[S] values end up crowded on the left side of the graph- makes drawing the straight line difficult and inaccurate.
For small [S], there can be large errors in Km and Vmax.
What are the disadvantages of the Hofstee-Eadie plot?
Can have large errors- both coordinates contain the dependent variable.
What are the advantages of the Hanes-Woolf plot?
There is equal weighting of the data, so a better fit of the straight line.
How does pH affect the rate of an enzyme catalysed reaction?
V follows a bell shaped curve.
