How Cells Grow - Bioprocess Engineering: Kinetics, Biosystems, Sustainability and Reactor Design - page 568

FIGURE E11-2.2 Monod growth equation fit to data in Excel.

m max ¼ 0.4036. The quality of the fit is shown in

Fig. E11-2.2 . Now that all the kinetic parameters are known, we can calculate or predict
the growth behavior of the cells in the culture. The parameters obtained this way are more
reliable than that from Example 11-1.

0.0974/h, K S ¼ 3.76 g/L, and YF X/S ¼

11.6. CE LL MAINTENANCE AND ENDOGENOUS META BOLISM

As discussed in Chapter 10, cell metabolism is complicated and simplification is possible
for any given focus. In section 11.4, we have learned how a complicated metabolic pathway

may be simplified based on our perspective or parameters that can be measured. Cell
growth-associated internal cell functions are not easily measurable; however, they play
important roles in kinetic behaviors. In this section, we look at simplifying the cell growth-
associated functions with a focus on their effects on growth needs.
To harness the free energy produced by catabolic processes in terms of high-energy phos-
phate bonds, in particular in the form of ATP, for subsequent use in the biosynthesis of
biomass constituents in the anabolism, the cellular content of ATP (and ADP) must be
controlled quite rigorously. As the turnover time of ATP is low (U. Theobald, J. Mohns,
M. Rizzi. Dynamics of orthophosphate in yeast cytoplasm, Biotechnology Letters 18(4):
461 e 466 APR 1996), there must be tight balancing of the energy-forming reactions (catabo-
lism) and the energy-utilizing reactions (the anabolism) inside the cell. In analogy to the tight
balancing of synthesis and consumption of ATP, the cell needs to balance the synthesis and
consumption of the cofactors NADH or NADPH, which have a small turnover time. Conse-
quently, the cell must exercise a strict control of the level of these compounds as well.

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