Final Project: Wai Shing Lee — The Circadian Rhythm and its Robustness

Biological systems are complex, yet out of the apparent complexity comes order, and the circadian rhythm is an example of it. In a traditional reductionist point of view, all biological processes ultimately boil down to chemical processes happening inside the body. However, the rate of chemical reactions are generally temperature dependent, yet experiments find that even simple organisms like fruit flies exhibit regular circadian rhythm over a wide temperature range. Thus, the circadian rhythm is indeed a robust system that can adapt to external disturbances. In this project, motivated by the above question, I study a model in a paper on modeling the circadian rhythm of fruit flies. The paper and results therein suggest the possibility of structures involving not only negative feedback of the protein PER on the gene per, but also a positive feedback loop through dimerization of PER. By doing so, it is found that the system can exhibit circadian like behavior over a wide parameter range. In addition, with reference to another paper, I also study a proposal on how a robust circadian rhythm can be obtained through additional mechanism which regulates the rate “constants” of chemical reactions.  Lastly, it is also pointed out that further connection with mechanism like inter-cellular communications may be important too.


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