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.
Why is the rate of reaction of an enzyme catalysed reaction affected by pH?
There is pH sensitivity in substrate binding. The substrate can be ionized. There can be protein structural changes at extreme pH values.
What are bisubstrate reactions?
Reactions that use two substrates and form two products.
What types of reactions can be bisubstrate reactions?
Transferases- functional group is transferred between the substrates.
Redox- reducing equivalents are transferred between substrates.
What is a sequential enzyme mechanism?
All substrates must combine with the enzyme before the reaction can occur and products can be released.
What is the difference between an ordered sequential mechanism and a random sequential mechanism?
Ordered- each substrate binds in a specific order and each product is released in a specific order.
Random- allows substrates to bind in any order and then products to be released in any order.
What is ping-pong kinetics?
One or more products are released before all of the substrates have bound to the enzyme.
How are the number of products/reactants specified in ping-pong kinetics?
As uni, bi, ter and quad.
- a reaction with one substrate and two products = uni bi
- a reaction with two substrates and two products = bi bi
What type of enzymes do not follow Michaelis-Menten kinetics and why?
Enzymes that are allosterically regulated, due to cooperativity.
