# Cameron M. Rehmani Seraji Week 6

## Purpose

• The purpose of the week 6 assignment is to construct models of the dynamics of yeast, nitrogen, and carbon. This will be accomplished by further studying the growth of yeast and how the state variables and parameters affect it. In particular, this assignment will focus on the central nitrogen metabolism processes project.

## Methods

• For this assignment, I decided to focus on the central nitrogen metabolism processes project.
• From the three readings, I selected the ter Schure et al 1995 paper and took notes.

## Results

### Hypothesis

• An increase in the ammonia feed rate would cause the yield of S. cerevisiae to remain constant. S. cerevisiae, ammonia, and glucose fit into the multiplicative nutrient use model because ammonia and glucose are both needed for S. cerevisiae to grow. The yield is constant because the residual ammonia concentration becomes limiting at dilution rates greater than 0.15 h^-1.

### State Variables

• y=concentration of yeast
• c=concentration of nutrient (ammonia or glucose)

### Differential Equations

• The system of differential equations I have generated are based on the multiplicative nutrient use model from Multiple Nutrients in Chemostat Assignment.
• My attempt at finding a system of differential equations for the model can be found here

### Explanation of Differential Equations

• Ammonia Consumption
• Du1 represents the concentration of ammonia being added to the fermenter(inflow).
• Dc1 represents the concentration of ammonia being taken out of the fermenter(outflow).
• y(c1/c1+k1)(c2/c2+K2) is the amount of ammonia and glucose being consumed by the yeast.
• Glucose Consumption
• Du2 represents the concentration of glucose being added to the fermenter(inflow).
• Dc2 represents the concentration of glucose being taken out of the fermenter(outflow).
• y(c1/c1+k1)(c2/c2+K2) is the amount of ammonia and glucose being consumed by the yeast.
• Yeast Growth
• yR(c1/c1+k1)(c2/c2+K2) represents the growth rate of the yeast as ammonia and glucose are being consumed.
• Dy represents the amount of yeast leaving the fermenter.

## Scientific Conclusion

• The ter Schure et al (1995) paper focused how concentrations of ammonia and glucose at different dilution rates affect the growth of yeast inside a fermenter. The multiplicative nutrient model was used to make differential equations for this model because the yeast is dependent on ammonia and glucose to grow. As the dilution rate increases, the residual NH4+ concentration decreases and the activity of the enzymes using NH4+, NADPH-GDH and GS, increased while the activity of the enzyme producing NH4+,NAD-GDH, decreased. I am unsure whether my hypothesis or the differential equations I have created are correct, so further explanation will be needed to improve my understanding.

## Acknowledgements

• Worked with Lauren M. Kelly in Seaver 120 on February 22nd.
• Except for what is noted above, this individual journal entry was completed by me and not copied from another source.
• Cameron M. Rehmani Seraji 01:22, 23 February 2017 (EST):

## References

• Dahlquist, Kam D. (2017) BIOL398-05/S17:Week 6. Retrieved from http://www.openwetware.org/wiki/BIOL398-05/S17:Week_6 on 22 February 2017.
• Schure, E. G., Sillje, H. H., Raeven, L. J., Boonstra, J., Verkleij, A. J., & Verrips, C. T. (1995). Nitrogen-regulated transcription and enzyme activities in continuous cultures of Saccharomyces cerevisiae. Microbiology, 141(8), 2019-2019. doi:10.1099/13500872-141-8-2019