Kinetics- what is rate and why do we care?
Why do we care about kineti cs (in biology)?
Biochemical reactions- e.g. Enzymes
Metabolic differences- people, different species → treat diseases
Engineering biochemical reactions
Receptor-ligand interactions
Which things bind faster/ slower? Why?
People, different species → understand and treat disease
What happens to drugs in body?
Where do they go?
How quickly they absorbed, distributed, metabolised, excreted (ADME)?
Drug effectiveness and toxicity
What is rate and why measure it?
Rate- change in something with respect to time
- e.g. Speed= Distance/ Time or m/s
In biology- amount, concentration or location change with respect time
-e.g. mmol/s, mmol-1dm-3min-1, μM min-1… etc
‘Thermodynamics’- tells us whether reaction can process spontaneously but doesn’t inform us about rate at
which reaction will proceed
- This information must be obtained experimentally
How do we measure reacti on rates?
Some form of change in product/reactant with time?
Spectroscopic- e.g. absorbance, fluorescence
Temperature changes- e.g. ITC
Mass changes- e.g. SPR
Conductivity
Electrochemical
For very fast reactions- used stopped flow or quench flow
For unimolecular reaction or protein and
ligand interaction:
At equilibrium:
But how quickly do we get to equilibrium? Even at equilibrium- reaction hasn’t stopped. We use rate constants (k)
to tell us how quickly each reaction can occur:
Define rate constant of forward reaction as k1 and reverse reaction as k-1
small k is used for rate constant. Big K is used for equilibrium constant
For unimolecular reaction- converted from A to products
How quickly does amount of [A] changes?
Rate at which A is converted to products is proportional to concentration
of A and rate constant k where x= order
, If we measure change in [A] over ti me for this reacti on:
This example follows zero order kineti cs
For zero-order kinetics- rate of reaction is independent of concentration of reactants
Reaction rate is constant- regardless of concentration of reactants present
Why? What does it mean?
X= order, which here= 0. Therefore:
Through the rearrangement and integration, equation of line:
Ethanol Metabolism exhibits zero order kineti cs
If we plot rate as functi on of concentrati on for zero order reacti on
Many reacti ons are dependent on concentrati on
For unimolecular reaction dependent on concentration:
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