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Purpose: To develop skills in thinking about and creating Stella model of reversible reactions.

Questions, Parameter Values, Thinking about the results, Variations (Backrground)

Model

Questions

• What can we say about the system even before we run a simulation of the model?
  • Is the system open or closed?
    • It is closed. The total mass of molecules does not change. It only changes its distribution between two states.
• What dynamics do we expect from the system?
  • How do we expect the amount of a molecule (proteinA, proteinB) change in relation to other molecules in the system?
    • As the concentration of protreinA goes down, we expect the concentration of proteinB to go up and vice versa. A positive change in proteinA, is a negative change in proteinB. And a positive change in proteinB is a negative change in proteinA.
  • How does it compare to the model created in Example 1?
  • How do we expect the reaction rates (forward and backreaction) to change in relation to the components?

Create and run the model in Stella.

Parameter Values

Try the following parameter values.

Thinking about the results: Exercises.

Do the reaction results show what we expect, if we run the simulation of the model?

What types of change do you expect to see given the reactionrates and starting amounts are equivalent?

Do the results vary if you change one of the initial stock values? If so, how?

What happens if you change the constant in "reactionrates" from 0.1 to some other value?

What happens if you change the starting amount of one of the molecules?

What happens if you change the "forward" and "backreaction" equations to negative values (-)?
Careful: This result may be different than you expect. This is one of Stella's quirks. Create an explanation for these results. Include a statement about the direction the arrows point.

Variations