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Mass action rate laws:

Mass action kinetics state that the rate of a reaction is the product of a rate constant (k) times (*) the mass(S). The mass in our case is concentration of the substrate (S) of the reaction. kS

Mass action kinetics can be used to model (approximate) the behavior of reversible and irreversible enzymatic reactions for unregulated enzymes that are not near saturation.

Modeling reversible and irreversible reactions with mass action kinetics.

• irreversible reactions (uni-directional)

  • Irreversible reactions are reactions that occur in only one direction. This includes uni-directional movement across a membrane through a channel and enzyme catalyzed reactions. For reactions with a single substrate, the rate law for the reaction is written k*S or simply kS.
  • Practice writing rate equations

 

• reversible (bi-directional)

• The phrase "reversible reaction" is often applied to at least two types of biological events. One event includes the reactions mediated by a single enzyme. This enzyme catalyzes the transition or transformation of molecules between two states. The second event is that the transition between the two states is mediated by two different enzymes. This latter event is the result of two opposing uni-directional reactions.

• Stella example and exercise: Example 1