CHEN 4800/5800: Bioprocess Engineering
University of Colorado, Spring 1996

Mid-term Test

A. Short Paragraph Answer Questions (10 points each)

1. Discuss the utility of thermostable enzymes, with a recent example of their applications.

2. Define energy charge, and discuss how it regulates the major metabolic pathways.

3. Explain the advantages of fed-batch cultures over the continuous cultures for the overexpression of foreign proteins in recombinant bacteria.

4. Explain the Pasteur effect and the diauxic growth of yeast in aerobic cultures and show how the chemostat cultures of yeast differs from the Monod model predictions.

5. Discuss the main elements required in a recombinant plasmid and their function in expressing foreign genes in bacteria.

B. Numerical Problems (25 points each)

1. In duplicating an experiment on inhibited enzyme kinetics, the reaction volume was accidentally doubled, thereby reducing the concentrations of enzyme, substrate and inhibitor each by half. The first experiment used the concentrations of substrate and inducer equal to K_m and K_I of the reaction respectively. If the initial rate determined in the second experiment was found to be 4/9 th of the initial rate measured in the first experiment, determine whether the inhibition is competitive or noncompetitive.

2. Bacterial cells, obeying Monod kinetics (µ = 0.9 hr -1, K_s = 0.5 g/l , and Y_x/s = 0.4 gdw/gS) are grown in a 10 liter chemostat. The substrate concentration in the feed is 20 g/l. What inlet feed flow rate will maximize the rate of cell mass produced? To increase the rate of cell mass production, a recycle stream is added to the chemostat, with a cell concentration factor C of 1.5, and recycle ratio of 1 and the dilution rate is doubled from the non-recycled chemostat. Calculate the new rate of cell mass production and compare it with the maximum rate from the simple chemostat.