The fermentation process is caused by the living organisms called yeast feeding on the sugar in the dough. As the yeast feed on the sugar they release CO² which causes the bread to rise but once the bread in the oven reaches 140° all the yeast are killed off and the fermentation process stops.
The nucleus contains the cells DNA(genetic material) which is basically the recipe for making proteins. mRNA is first transcribed off of DNA and then in translated(by ribosomes) to polypeptides(proteins).