32.443 Introduction to Biochemical Engineering

1. (10 pts) List the steps for the initial purification by solvent extraction into organic solvent and back into water for a molecule that is a weak organic acid. Start with a dilute aqueous solution at neutral pH and state the pH and very rough solvent ratios for these extraction steps.
2. (10 pts) Identify the specific compound, but when R stands for any simple hydrocarbon group you should just state what type of compound, e.g., fatty acid.
   a. CH3 - ( CH2 )n - COOH where n is from 14 to 16
   b.

     CH2 - CO - ( CH2 ) n - CH3
     |
     CH - CO - ( CH2 ) n - CH3
     |
     CH2 - CO - ( CH2 ) n - CH3
   

   c. this was a sketch of lyxose
   d. sketch of an amino acid
   e. sketch of I can't remember
3. (6 pts) What is concentration polarization of a membrane and why is it important ?
4. (5 pts) Describe how to sample a large fermenter that might easily be contaminated.
5. (5 pts) List some reasons why continuous sterilization can be better than batch sterilization of media.
6. (5 pts) Explain with equations why two different types of microorganisms should not be able to coexist in a chemostat.
7. (5 pts) How are cells ruptured (in big equipment) to release a product ?
8. (5 pts) Comment on going directly to the next step of solvent extraction or ion exchange without first removing solids from the final fermentation broth by filtration.
9. (5 pts) How can you tell quickly if a bioprocess is contaminated by unwanted organisms ?
10. (4 pts each) SHORT ANSWERS
    a. define diauxie
    b. define commensalism
    c. define auxostat
    d. write a mass balance differential equation for the nutrient concentration in a chemostat
    e. why is it difficult to estimate the maximum value of m when the data are plotted as m versus concentration of limiting nutrient ?
    f. What is cornsteep liquor ?
    g. Say something meaningful about Power Number as an aid to scale up of mixing.
    h. What is a streptococcus ?
    i. With respect to contamination, why is it easier to operate a process with yeast than with cells from plants or animals ?
    j. What tests will distinguish between live and dead cells ?
    k. What method of air sterilization is most common ?