Team:Paris/Analysis/Construction

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Model construction


Contents

Introduction

  • This preliminary approach is mainly based on a bibliographical work. In fact, it is important to understand that with this approach, we did not intend to design the most accurate model possible. We found essential to choose only parameters that could be found in literature. The main goal was to get quickly a first idea of the way our system could behave.
  • In this section, we will present the model we chose to describe the evolution of our system's concentrations.

Classical model and temporal rescaling

  • Classically we use the following equation to model gene interactions (see for example in [1]) :


Classical equation.jpg


where [Y] denotes the concentration of Y protein and γ its degradation rate (which unit is time-1).

  • We did a lot of bibliography work and found many interesting expressions found in S.Kalir and U. Alon article. We also kept the parameters values. When we did not find relevant information, we chose a classical Hill function.
  • We normalized every concentration, so that their value would range between 0 and 1. Indeed, we found it necessary because we needed to be able to compare the respective influences of these concentrations.
  • Furthermore, it is important to note that this degradation rate represents both the influence of the degradation and dilution. We assume that the degradation can be neglected compared to the dilution caused by the cell growth. Thus, every degradation rates are equal. We kept the designation “degradation rate” for convenience, so as not to mix up with the dilution that might occur elsewhere.
  • We therefore wanted to have a proper time scale. We then set the degradation rates, γ ,to 1. Since we can know easily the value of the real half-time, we may know the real timescale out of our computations. Then we have:


Gamma Expression.jpg


  • Finally, the key problem with a dynamic system consists in the fact that adding a new equation gives a more detailed idea of the overall process, but one looses meaning by doing so since new undefined parameters appear. Hence, it becomes hard to link those parameters with a biological meaning and reality. In that respect, we chose not to introduce the mRNA state between transcription and translation in our model. We presented things as if a protein would act directly upon the following.

Conclusion

We finally obtained the following equations :

Eqn flhDC.jpg
FliA dynamics.jpg
CFP.jpg
YFP.jpg
Eqn EnvZ-RFP.jpg

and the following parameters :

Parameter Table
Parameter Meaning Original Value Normalized Value Unit Source


γ Degradation rate 0.0198 1 min-1 wet-lab
βFliA FlhDC activation coefficient 50 0.1429 min-1 [1]
β'FliA FliA activation coefficient 300 0.8571 min-1 [1]
βCFP FlhDC activation coefficient 1200 0.8276 min-1 [1]
β'CFP FliA activation coefficient 250 0.1724 min-1 [1]
βYFP FlhDC activation coefficient 150 0.3333 min-1 [1]
β'YFP FliA activation coefficient 300 0.6667 min-1 [1]
βEnvZ-RFP FlhDC activation coefficient 100 0.2222 min-1 [1]
β'EnvZ-RFP FliA activation coefficient 350 0.7778 min-1 [1]
βFlhDC Maximum production rate 1 min-1
nenvZ Hill coefficient 4 ¤
θenvZ Hill characteristic concentration 0.5 c.u

Now you have had a good overlook of our model, go see a more detailed justification, where our normalization choices are thouroughly explained!

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Have a look at our detailed justification! Have a look at our Akaike criteria!

Bibliography

  • [1] Shiraz Kalir, Uri Alon. Using quantitative blueprint to reprogram the dynamics of the flagella network. Cell, June 11, 2004, Vol.117, 713-720.