Practice Problems - MFA- 2013

Metabolic Engineering: Practice Problems Solutions will be posted Monday 11/11/13. 1. Short answer a) Why is it useful to study metabolic pathways using metabolic flux analysis? b) You are working with a metabolic pathway in which two reactions in the pathway are linearly dependent. You also observe that flux is evenly split between the two reactions. How would you handle this linear dependency? 2. Metabolic flux analysis in an overdetermined system: Anaerobic fermentation in a microbial system occurs via the following reactions: (1) -0.15 NH3 - 2.42 ATP - 1.12 CH2O +CH1.62O0.53N0.15 + 0.12 CO2 + 0.185 NADH = 0 (2) -1.5 CH2O + CH2O0.5 + 0.5 CO2 + 0.5 NADH + 0.5 ATP = 0 (3) - CH2O0.5 - 0.5 NADH + CH 3O0.5 = 0 (4) - CH2O - ⅓NADH - ⅓ ATP + CH 8/3O = 0 where CH1.62O0.53N0.15 = biomass, CH2O = glucose, CH2O0.5 = acetate, CH 3O0.5 = ethanol, CH8/3O = glycerol (a) Write the stoichiometry for the four reactions above using matrix notation. Hint: Define your intracellular metabolites as NADH, ATP, and acetate. (b) Define your rate vector v as:

v1 μ v v = v2 = 2 ve v3 vg v4

( )( )

where µ, νe, and νg are the specific growth rate, rate of ethanol production, and rate of glycerol production, respectively. Suppose that you measure the rate of biomass formation µ and calculate ν2, νe, and νg. Express vc in terms of GcT, GmT, and vm using Equation 8.8. Calculate vc when µ = 0.1 h-1. What is the rate of acetate formation when µ = 0.1h-1? Could you calculate vc using Eqn 8.8 if you measured biomass and ethanol? Why or why not?