Reaction Kinetics PR L8-10 Flashcards
Does Biology exist in a state of equilibrium?
No
Lots of enzymes act to drive chemical reactions in a specific and timely way
What types of rxn rates are important in biology?
Transport across membs
protein folding
enzyme catalysed rxns
What is the rate of a reaction?
A change in concentration of a reactant or a product as a function of time (M/s)
What is the rxn rate law?
The rxn rate law is a mathematical expression which relates the rate of a reaction to the concentration of each reactant.
Why are zero order reactions unusual?
zero order rxns are always initiated / rates are determined by physical effects e.g. light, pressure, temp
The rate of rxn is INDEPENDENT to the concentration of the reactants
Difference between steady state and equilibrium?
The steady state is a situation in which all variables are constant in spite of an ongoing process. Unlike equilibrium the net reaction rate is not 0.
What are the limitations for steady state kinetics?
Not easy in complex systems to get a high level of detail for individual steps in a rxn and provides only two parameters (kcat and km using michaelis menten methods)
Can not determine individual rates of a complex rxn scheme using the steady state.
How do you determine individual rates of a complex rxn scheme?
Do not use steady state
Analysis in the PRE steady state (Also known as transient kinetics)
Pre steady state methods monitor events before the steady state is reached.
Measuring a single turnover of each step in the reaction process.
Measure the rxn rates using stopped flow apparatus-As the substrates are mixed together this apparatus can measure the change in the physiochemical properties of either the product, substrate or enzyme.
Can measure individual parameters and steps by using this technique to look at single turnovers of an enzyme catalysed reaction
Performing and analysing rxns in the pre steady state
Use concentrations of substrate that are in excess of enztme ( minimum 3-4 fold). This ensures that ES complexes are significantly populated and the rate becomes pseudo-first order (easier to analyse first order form as can readily be fitted to an exponential curve).
In this instance S does not appreciably change as ES is formed
Application of pre steady state kinetics to identify rate limiting steps in enzyme catalysed reactions
The steady state rate, as given by kcat reports the rate of the slowest state ( describes process in its entirety)…but if we apply pre steady state methods we can measure rxn rates in isolation and assign rxn rate constants to digestible chunks in a complex rxn pathway
What is the by-stander effect and why do u need it?
Not only killing the tumour cell expressing the enzyme but also killing the cells around the tumour which is important since adenoviral vector is not always 100% efficient
NTR nitroreductase
NTR + CB1954(Pro drug)-> compound which forms inter strand DNA crosslinks which kills tumour cells are there are difficult to repair as dsDNA by cellular machinery
It irreversible attaches DNA strands together.
