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Engineering of Biological Processes Lecture 3: Yields and stoichiometry

Engineering of Biological Processes Lecture 3: Yields and stoichiometry. Mark Riley, Associate Professor Department of Ag and Biosystems Engineering The University of Arizona, Tucson, AZ 2007. Objectives: Lecture 3. Biosynthetic processes (anabolic) Case studies - cholesterol

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Engineering of Biological Processes Lecture 3: Yields and stoichiometry

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  1. Engineering of Biological ProcessesLecture 3: Yields and stoichiometry Mark Riley, Associate Professor Department of Ag and Biosystems Engineering The University of Arizona, Tucson, AZ 2007

  2. Objectives: Lecture 3 • Biosynthetic processes (anabolic) • Case studies - cholesterol • Stoichiometry and modeling cellular requirements • "You are what you eat"

  3. Stoichiometry • Provides information on fundamental constraints • Substrate conversion to product • Cell mass from substrate

  4. Yields and yield coefficients • Mass based = “kg” of this from “kg” of that • Y (output / input) • Y x/s • Y p/s • Y ATP/O2 • Ymx/s maximal yield of cell mass from substrate

  5. YIELD Yield • Overall • Instantaneous • Ratio of rates • Ratio of yields • Theoretical = Y • Observed = Y’

  6. Cell metabolism • Y’ lactate / glucose = ranges from 2 to 0 based on environment • The basic reaction is: • Glucose + 2 Pi + 2 ADP → 2 Lactate + 2 ATP + 2 H2O

  7. Bacterial dry cell weight [mg/L] Slope = dX/dS 7 (mg/L) / (g/L) Glucose [g/L] • Yield of cell mass from substrate • Y x/s

  8. Aerobic Yx/s=58 mg/mol Bacterial dry cell weight [g/L] Anaerobic Yx/s=22 mg/mol Glucose [mM]

  9. Cell composition CHxOyNz

  10. In a very simplistic interpretation of metabolism, the following applies: • Cells + medium + O2 (sometimes) → more cells + product + CO2 + H2O • Medium contains sugars, amino acids, cofactors and the elements in the previous table.

  11. Stoichiometric calculations • Based on 1 mole of C in the input • CHmOn + a O2 + b NH3→ • c CHaObNd + dH2O + eCO2 • This is normalized to 1 mole of C. Could also be normalized to 1 mole of the C source compound • Perform elemental balances to determine the unknown values of the cofactors

  12. Example • C6H12O6 + a O2 + b NH3→ • c C4.4H7.3O1.2N0.86 + dH2O + eCO2 • 2/3 of the glucose C goes to biomass • What are the stoichiometric coefficients, and Yx/s, Yx/O2? MWglucose = 180 MWcell = 89.62 MWoxygen = 32 MWammonia = 17

  13. Generalized growth reaction • C6H12O6 + a NH3 + b O2→a CH1.8O0.5N0.2 + • b CHxOyNz + gCO2 + dH2O • Normalized to 1 mole of carbon source compound • Where a, b, a, b, g, d, x, y, z depend on the type of cell involved. • a, b, a, b, g, d, are stoichiometric coefficients • When little info is available about cell composition, use an approximated cell composition of CH1.8O0.5N0.2 • This yields a MW of a cell ~ 24.6

  14. Generalized growth reaction C6H12O6 + a NH3 + b O2 → a CH1.8O0.5N0.2 + b CHxOyNz + gCO2 + dH2O g of cells from g of glucose

  15. Lack of information • Unfortunately, the elemental balances often do not provide enough information to completely solve for the stoichiometric coefficients.

  16. Respiratory quotient • RQ = YCO2/O2 • Molar basis • Moles of CO2 produced from moles of O2 • Provides information on the metabolic state of the cell • A high RQ means that much CO2 is produced and hence the metabolism is operating at high efficiency

  17. Aerobic metabolism • CHmOn + a O2 + b NH3→ • c CHaObNd + d CHxOyNz + eH2O + fCO2 • RQ = ?

  18. Degree of reduction • Electron balance • = # of available electrons / g of atomic C • Or, this can be described as: • = # of available electrons / # of C’s • Provides another independent equation

  19. C = 4 H = 1 N = -3 O = -2 P = 5 S = 6 CO2 = +4 (C) + -2 (O) = 0 C6H12O6 = 6(4) + 12(1) + 6(-2) = 24 g = 24 / 6 (# carbon atoms) = 4 C2H5OH = 2(4) + 6(1) + (-2) = 12 g = 12 / 2 (# carbon atoms) = 6 Degree of reduction

  20. Example – yeast grown on glucose • C6H12O6 + 0.48 NH3 + 3 O2→ • 0.48 CH1.8O0.5N0.2 + 3.12CO2 + 4.32H2O • To grow yeast to 50 g/L in a 100,000 L reactor, determine: • a) mass of glucose and ammonia required • b) O2 required • c) Yx/s and YX/O2 MWglucose = 180 MWcell = 24.6 MWoxygen = 32 MWammonia = 17

  21. HW #1 questions • What kind of cell would you use to produce androstenedione? Your answer should describe the attributes of such a cell (don't just state, "a cell that produces andro"). An answer longer than 4 sentences is too much. • Producing cholesterol is an energy intensive process. How much energy (in terms of # of ATP molecules) is consumed in producing one cholesterol molecule from a source of glucose?

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