Team:BHSF/Design
Project Design
In bread-baking, yeasts need to be added to different amount to the yeast before the dough is fermented a specific time to complete the dough’s preparation. While both over-fermentation and under-fermentation can negatively affect the quality and taste of the bread, setting the yeast to stop its life process after a certain time can greatly reduce this problem.
In order to design a suitable timing machinery, we took advantage of a toggle switch to help control the time in which the yeasts perform their fermentation function. By using the bistable structure and mechanism of toggle switch, the circuit can proceed for a certain time before the toggle switch transfers from one stable state to another.
What is the function of our circuit?
To manipulate the yeast and to make sure it stops functioning in a certain time, the bistable structure of the toggle switch is crucial since it can maintain or terminate the process of the circuit as long as the initial balance between the concentration of the two proteins in the toggle switch remain intact.
A auxotroph yeast needs the circuit that synthesizes the deficient nutrient to remain active, so it can continuously perform its function. As soon as this synthesis process ends, the life-activities of the yeast quickly terminates.
The Leu sequence synthesizes leucine, an essential nutrient that supports the yeast's life activities, and the promoter of the sequence is inhibited by a product of the toggle switch: LacI.
Initiation of the Circuit
To start the process of the circuit, galactose activates the pGAL promoter to start the expression of integrase, which in turn initiates expression of LacI by aligning the promoter to lacI gene, of which the product would induce the state transition of the bistable switch.
The Functioning of Toggle Switch
The product of Lacl inhibits both the nutrient sequence, Leu, and one component sequence of the toggle switch, Cl, both of which are promoted by a pLac promoter.
This design enables the both products of the toggle switch to remain at a relatively stable level of concentration. As soon as the state of the toggle switch transfers due to overexpression of lacI, insufficient promotion of the expression of the nutrient sequence would deprive the yeast of the crucial nutrient and quickly end its metabolic activities.
