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STOICHIOMETRY OF MICROBIAL GROWTH AND PRODUCT FORMATION PTT 203 Biochemical Engineering WEEK 13 BY: MADAM NOORULNAJWA DIYANA YAACOB

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Lets Try Assume that experimental measurement for certain organisms have shown that cells can convert two- thirds (wt/wt) of the substrate carbon (alkane or glucose) to biomass a) Calculate the stoichiometric coefficients for the following biological reactions: Hexadane: C 16 H 34 + aO 2 + bNH 3 c (C 4.4 H 7.3 N 0.86 O 1.2 ) + dH 2 O + eCO 2 Glucose: C 6 H 12 O 6 + aO 2 + bNH 3 c (C 4.4 H 7.3 N 0.86 O 1.2 ) + dH 2 O + eCO 2 b) Calculate the yiels coeeficients Yx/s (g dw cell/g substrate), Yx/o2 (g dw cwll/ g O2)

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7.4 Theoretical Predictions of Yield Coefficient In aerobic fermentation, the growth yield per available electron in oxygen molecules is approximately 3.14 gdw/electron when ammonia is used as the nitrogen sources. The number of available electron per oxygen molecule is four. When the number of oxygen molecules per mole of substrate is known, the growth yield coefficient Yx/s can easily be calculated

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Consider the aerobic catabolism of glucose: C6H12O6 + 6O2 6 CO2 + 6 H2O The total number of available electrons in 1 mole glucose is 24. The cellular yield per available electron is Yx/s = 24 (3.14)= 76gdw cell/mol The predicted growth yield coefficient is Yx/s= 76/180= 0.4 gdw cell/g glucose

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The ATP yield (Y x / ATP ) in many anaerobic fermentation is approximately 10.5 gdw cells/ mol ATP. In aerobic fermentation this yield varies between 6-29. When the energy yield of metabolic pathway is known (N moles of AT produced per gram of substrate consumed), the growth yield Yx/s can be calculated using the following equation Y x/s = Y x / ATP N

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Do it Yourself Example 7.2

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