Stochastic model of mating decision control in yeast through the scaffold protein Ste5
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- Institutt for biologi 
High throughput technologies in genetics laid the foundations for systems and synthetic biology. Systems and synthetic biology became an important topic in biology research. It was used in research to investigate the behavior and relations of all elements in biological systems while it was functioning. The intracellular signal transduction pathway, where the haploid yeast Saccharomyces cerevisiae responds to the mating pheromone in its surroundings, is believed to be one of the best understood and studied signaling pathways in eukaryotes. In Malleshaiah et al. (2010) it was introduce a general model of the switch-like mating decision in the haploid yeast S.cerevisiae. The general model consisted of the Ptc1, Ste5, and Fus3 circuit with two-stage binding that exhibited zero-order ultrasensitivity. The model of a switch-like mating decision in the haploid yeast S. cerevisiae was modified in order to perform both deterministic and stochastic analysis. Deterministic analysis was conducted with mean measurements. Furthermore, stochastic simulations of the modified model were conducted. Hence, it was possible to analyze the fluctuations in the system by calculating the mean, standard deviation, coefficient of variation and fano factor. This gave an indication of the switch. It was calculated the mean values of free and bound Ste5 molecules and the amount in every single complexes. Due to an increase of the Ste5 and Fus3 molecules, the mean of free and bound Ste5 molecules were changed. By calculating the mean of bound Ste5 molecules in single complexes, the distribution of bound Ste5 molecules was about the same. The parameter values were conducted from literature, which were used in both the deterministic and stochastic simulations. The system was not affected by kinetic rate changes and thereby robust.